No full-text available
To read the full-text of this research,
you can request a copy directly from the author.
Some genetic consequences of ice ages, and their role in divergence and speciation
Abstract
The genetic effects of pleistocene ice ages are approached by deduction from paleoenvironmental information, by induction from the genetic structure of populations and species, and by their combination to infer likely consequences. (1) Recent palaeoclimatic information indicate rapid global reversals and changes in ranges of species which would involve elimination with spreading from the edge. Leading edge colonization during a rapid expansion would be leptokurtic and lead to homozygosity and spatial assortment of genomes. In Europe and North America, ice age contractions were into southern refugia, which would promote genome reorganization. (2) The present day genetic structure of species shows frequent geographic subdivision, with parapatric genomes, hybrid zones and suture zones. A survey of recent DNA phylogeographic information supports and extends earlier work. (3) The grasshopper Chorthippus parallelus is used to illustrate such data and processes. Its range in Europe is divided on DNA sequences into five parapatric races, with southern genomes showing greater haplotype diversity - probably due to southern mountain blocks acting as refugia and northern expansion reducing diversity. (4) Comparison with other recent studies shows a concordance of such phylogeographic data over pleistocene time scales. (5) The role that ice age range changes may have played in changing adaptations is explored, including the limits of range, rapid change in new invasions and refugial differentiation in a variety of organisms. (6) The effects of these events in causing divergence and speciation are explored using Chorthippus as a paradigm. Repeated contraction and expansion would accumulate genome differences and adaptations, protected from mixing by hybrid zones, and such a composite mode of speciation could apply to many organisms.
... Temperature is considered to be the main factor leading to migration of these animals. A decrease leads to migration to the southern refugia, while an increase triggers a reverse migration from the refugia to previuously occupied habitats (Hewitt, 1996). Each species underwent several migrations of this kind during the Quaternary (Hewitt, 1996;Kalyabina-Hauf & Ananjeva, 2004;Joger et al., 2007). ...
... A decrease leads to migration to the southern refugia, while an increase triggers a reverse migration from the refugia to previuously occupied habitats (Hewitt, 1996). Each species underwent several migrations of this kind during the Quaternary (Hewitt, 1996;Kalyabina-Hauf & Ananjeva, 2004;Joger et al., 2007). Some authors believe that migrations to southern refugia lasted until the Pliocene (Kalyabina-Hauf & Ananjeva, 2004). ...
... If both, then they had already managed to 'get used to' to each other and divide their habitats and hunting areas, which also requires time. Hewitt (1996) also provided rates of dispersal, not for animals but for plants. These rates for different species are between 50 and 500 m/year. ...
I do not support modern ideas regarding the sheltering of northern species of amphibians and reptiles in southern refugia during glacial periods. The current article presents arguments that reject the traditional point of view. The northern species did not fall within southern refugia, and therefore new forms (haplotypes) appeared within the periglacial hyperzone. I describe how these processes may have taken place.
https://doi.org/10.1093/biolinnean/blad030
... However, the similar phylogeographic subdivision of different taxa could result from different causal factors at different times (i.e., pseudocongruence in Soltis et al., 2006;Lyman and Edwards, 2022). Although most of the known discontinuities have been thought to be caused by range shifts from multiple refugia located on the opposite sides of physical barriers during the Quaternary glacial periods (Hewitt, 1996;Jaramillo-Correa et al., 2009), a few studies detected a more ancient origin of phylogeographic breaks and proposed that geographic barriers such as the Mississippi River and the Appalachian Mountains may have served to block gene flow before the Pleistocene (Burbrink et al., 2008;Herman and Bouzat, 2016). Resolving the underlying causal factors in promoting genetic discontinuity requires applying several analytical techniques to uncover the intraspecific genetic variations and test related phylogeographic hypotheses (Lyman and Edwards, 2022). ...
... A typical example of how the genetic diversity and population structure of species is used to reconstruct possible demographic history is the prediction of potential glacial refugia by identifying genetic diversity "hotspots" (Hewitt, 1996(Hewitt, , 2000Lumibao et al., 2017). Quaternary climate changes, especially Pleistocene glacial cycles, have frequently been invoked to account for a signature of higher genetic diversity in populations from refugial areas (Hewitt, 1996(Hewitt, , 2000. ...
... A typical example of how the genetic diversity and population structure of species is used to reconstruct possible demographic history is the prediction of potential glacial refugia by identifying genetic diversity "hotspots" (Hewitt, 1996(Hewitt, , 2000Lumibao et al., 2017). Quaternary climate changes, especially Pleistocene glacial cycles, have frequently been invoked to account for a signature of higher genetic diversity in populations from refugial areas (Hewitt, 1996(Hewitt, , 2000. Classic hypotheses posited that temperate taxa from ENA were mainly preserved in southern refugia located in southeastern USA, including the Gulf Coast, peninsular Florida, and central Texas, during the glacial period (Soltis et al., 2006;Bemmels et al., 2019). ...
Premise
Glacial/interglacial cycles and topographic complexity are both considered to have shaped today's diverse phylogeographic patterns of taxa from unglaciated eastern North America (ENA). However, few studies have focused on the phylogeography and population dynamics of wide‐ranging ENA herbaceous species occurring in forest understory habitat. We examined the phylogeographic pattern and evolutionary history of Podophyllum peltatum L., a widely distributed herb inhabiting deciduous forests of ENA.
Methods
Using chloroplast DNA (cpDNA) sequences and nuclear microsatellite loci, we investigated the population structure and genetic diversity of the species. Molecular dating, demographic history analyses, and ecological niche modeling were also performed to illustrate the phylogeographic patterns.
Results
Our cpDNA results identified three main groups that are largely congruent with boundaries along the Appalachian Mountains and the Mississippi River, two major geographic barriers in ENA. Populations located to the east of the Appalachians and along the central Appalachians exhibited relatively higher levels of genetic diversity. Extant lineages may have diverged during the late Miocene, and range expansions of different groups may have happened during the Pleistocene glacial/interglacial cycles.
Conclusions
Our findings indicate that geographic barriers may have started to facilitate the population divergence in P. peltatum before the Pleistocene. Persistence in multiple refugia, including areas around the central Appalachians during the Quaternary glacial period, and subsequent expansions under hospitable climatic condition, especially westward expansion, are likely responsible for the species’ contemporary genetic structure and phylogeographic pattern.
... We also investigated the temporal scale at which gene flow probably occurred since the last glacial maxima (LGM). Based on the species distributional patterns and Ploeger's (1968) hypothesis, we predicted that the species population genetic structure should reflect Pleistocene vicariant events, such as isolated refugia and subsequent population expansion following deglaciation (Hewitt 1996), the signature of which can be inferred using genetic data (Beaumont 2010). ...
... In the Pacific Ocean basin, samples were collected from Harlequin Duck wintering sites during the autumn or winter of 1995of , 1996of (Pierson et al. 2023, or were obtained from museum specimens. Flightless birds were captured by funnelling birds into net pens using sea kayaks (for blood samples), or by shotgun (for muscle samples). ...
Species distributions are often indicative of historical biogeographical events and contemporary spatial biodiversity patterns. The Harlequin Duck Histrionicus histrionicus is a sea duck of conservation concern that has a disjunct distribution, with discrete portions of its range associated with northern Pacific and Atlantic Ocean basins. Movement data indicate migratory connectivity within regions of each ocean basin but not cross‐continent dispersal, suggesting that genetic structuring could exist at multiple spatial scales. Little is known regarding the impacts of past vicariance events on the species phylogeographical structure and historical demography, or rates of gene flow at different spatial scales. We used data from microsatellite loci and mitochondrial DNA (mtDNA) sequences to quantify levels of genetic diversity within, and the extent of spatial genetic differentiation among locations sampled at multiple spatial scales across the species range. Samples were collected at nonbreeding locations, which represent groupings appropriate for characterizing genetically differentiated subgroups at regional and continental scales. Collectively, genetic data and coalescence modelling suggested that individuals colonized regions currently occupied within both ocean basins in the Holocene from a single refuge in the Atlantic. Further, it seems likely there was secondary contact with lineages derived from populations in Asia, based on the shallow species‐wide mtDNA phylogeny and high incidence of recently derived private mtDNA haplotypes. Estimates of inter‐location variance in microsatellite allele and mtDNA haplotype frequency were moderate and significant between western (Pacific – North America) and eastern (Atlantic – North America, Greenland and Iceland) ocean basins and among sampling groups within each ocean basin. Genetic differentiation among sampling groups was particularly evident at the species distributional margins in the Atlantic (Iceland) and the Pacific (Shemya Island) Ocean basins. Coalescent modelling results suggest that contemporary spatial genetic patterns in the species arose through the combined influences of secondary contact, shared ancestry and gene flow after the last glacial maxima.
... Hewitt, 1996;Hofreiter & Stewart, 2009). Others were captured in isolated refugia, where the climate remained reasonably mild and humid (Bennet & Provan, 2008;Feliner, 2011;Fu & Wen, 2023;Hewitt, 1996;Tarkhnishvili et al., 2012). ...
... . Others were captured in isolated refugia, where the climate remained reasonably mild and humid (Bennet & Provan, 2008;Feliner, 2011;Fu & Wen, 2023;Hewitt, 1996;Tarkhnishvili et al., 2012). In these refugia, they continued to evolve, and populations from isolated landscape patches diverged genetically and phenotypically (Avise, 2000;Hewitt, 2001;Mutanen et al., 2012;Petit et al., 2003;Vila et al., 2005). ...
Large‐scale barcoding projects help to aggregate information on genetic variability of multiple species throughout their ranges. Comparing DNA sequences of both non‐conspecific and conspecific individuals from distant parts of their ranges helps to compare level of genetic isolation‐by‐distance patterns in different species and adaptive types. We compared mitochondrial CO1 gene sequences of 223 spiders from Georgia (Caucasus), representing 124 species and eight families, with 3097 homological sequences from spiders mostly from Europe, but also from other parts of the World. In most families, a significant isolation‐by distance pattern was observed on family level. On species level, a significant isolation‐by‐distance was observed in 40 species, although this low proportion is most likely related to a lack of data. Simultaneously, remarkable differences in spatial structure were shown for different species. Although the majority of the studied species have a broad western Palearctic range, web‐building spiders from families Araneidae, Theridiidae, and Linyphiidae are less isolated spatially than flower spiders (Thomisidae), jumping spiders (Salticidae), wolf spiders (Lycosidae), sac spiders (Clubionidae), and ground spiders (Gnaphosidae). This pattern is related with more common ballooning in web building than in actively hunting spiders, which commonly remain isolated since preglacial time. Ground spiders build the most isolated populations in the Caucasus.
... Glacial cycling can produce recurrent range expansions and contractions as climatic 33 conditions shift, and populations respond (Hewitt 1996 When divergent lineages come into contact, latent reproductive isolation is exposed. If 71 hybrids are less fit than parents, selection on reproductive barriers may reinforce divergence, Together, previous work suggests that speciation outcomes may not be uniform or 89 predictable across a species' range (Cutter 2012(Cutter , 2015. ...
... Furthermore, outcomes to contact may 90 differ across contact zones due to phylogeographic context and eco-evolutionary history. Yet, 91 few studies have sought to directly compare how outcomes of contact may vary across a range 92 (but see Mandeville et al. 2015), or whether variation in outcomes to contact is associated with 93 paleoclimatic range dynamics (but see Hewitt 1996Hewitt , 2000Hewitt , 2004 Carolina (RE; here, the rear-edge contact zone) and Pennsylvania (LE; here, the leading-edge 129 contact zone), (Fig. 1A). A contact zone between the Eastern and Appalachian lineages has also 130 been found in Virginia (VA). ...
Replicability of speciation and the maintenance of divergence after contact are poorly characterized processes, particularly in context of phylogeography and post-glacial range dynamics. Using contact zones located at the leading- and rear-edges of a species’ range, we examined variation in outcomes to contact between divergent lineages of Campanula americana. We investigated whether contact zones vary in quantity and directionality of gene flow, how phylogeographic structure differs between contact zones, and how historic range dynamics may affect outcomes to contact. We found that all contact zones formed at similar times via secondary contact yet detected significant admixture in only the rear-edge contact zone. Across all contact zones, gene flow was asymmetric. Our results emphasize the dependence of speciation processes on phylogeographic structure, demographic history, and paleoclimatic range dynamics. Our results suggest that caution need be taken when treating species as cohesive or uniform evolutionary units.
... These troglobitic arthropods are excellent models for exploring evolutionary patterns and diversification in subterranean aquatic and terrestrial environments. Several studies showed that intraspecific genetic diversity is spatially structured, with more diverse areas often coinciding across multiple species (Hewitt 1996), which results in genetic diversity hotspots (Carnaval et al. 2014). Nevertheless, few studies have incorporated comparative phylogeography in the identification of priority areas for conservation (Carvalho et al. 2017). ...
... Conservation efforts should also target nearby areas in the Abreu Stream microbasin, which holds more than half of the identified OTUs (10, eight of which are exclusive) in a small 15 square kilometer region. Such concentration is in line with studies that indicated that areas of higher genetic diversity are often coincident among several species (Hewitt 1996), resulting in hotspots of genetic diversity or concentrations of phylogeographic endemism (Carnaval et al. 2014). The second priority area includes localities in the Cote Stream microbasin. ...
One of the most important steps in identifying priority areas for conservation is the assessment of species richness and their extinction risks. While most species remain undescribed, the identification of cryptic lineages is frequent in phylogenetic and phylogeographic studies. This is particularly common in troglobites, exclusively subterranean organisms. The Jandaíra Formation, in the Brazilian semiarid, combines the occurrence of extensive karstic areas with hundreds of caves and subterranean aquifers in a region with intense paleoclimatic changes. This region is recognized for the richness of troglobitic species, some of which are widely distributed in heterogeneous areas. This suggests cryptic lineages that can be differentially exposed to anthropogenic threats, with distinct extinction risks regarding the nominal taxa of which they putatively belong. To test it, a large sampling was conducted and, by means of lineage delimitation analyses, the genetic structure of four troglobitic taxa, three aquatic and one terrestrial, was evaluated. In addition, the extinction risk of these lineages was assessed and priority areas for conservation were identified. The results indicated that while Cirolanidae sp. 1 (Isopoda) is a single species widely distributed, Cirolanidae sp. 2, Potiberaba porakuara (Amphipoda) and Kinnapotiguara troglobia (Hemiptera) present an extensive diversity of cryptic and endemic lineages, most of which are likely new threatened species. Furthermore, two priority areas for conservation of these lineages were identified. Thus, comparative phylogeography may represent a first step in the conservation of subterranean taxa, indicating areas that should be prioritized in a context of increasing threats and dwindling conservation resources.
... Many reptiles and amphibians have a limited dispersal capacity (Sinsch 1991;, are highly dependent on local environmental conditions for reproduction and development Blaustein et al. 2001;Jensen et al. 2018) and are generally considered to rely more heavily on external conditions than thermoregulating species (Deutsch et al. 2008;Bestion et al. 2015;Pie et al. 2017;Rolland et al. 2018). On the other hand, while these traits may be negative for local persistence during climate change, studying the demographic history of species with a narrow climatic niche in a geographic context can simultaneously provide important insights about the location and size of regions that have remained climatically stable over longer time scales (refugia; Hewitt 1996Hewitt , 2004Araújo et al. 2008). Thus, the study of climate change resilience in reptiles and amphibians is of particular interest due to their potential vulnerability under changing external conditions and terrestrial ectotherms are at the same time highly suited to evaluate how climatic stability may vary across landscapes. ...
... Whereas ecological generalists may be able to track suitable habitat during periods of change, ecological specialists are locally trapped and may go extinct with the disappearance of microhabitat (Moussalli et al. 2009;Garcia-Porta et al. 2019;Nguyen et al. 2019). Ectotherms may therefore be particularly dependent on geographic regions that have served as evolutionary refugia in the past and such refugia have likely shaped diversity patterns at a macroevolutionary scale for many reptiles and amphibians (Hewitt 1996(Hewitt , 2008Schneider and Moritz 1999;Beheregaray 2008;Byrne et al. 2008;Carnaval et al. 2009;Moussalli et al. 2009;Noble et al. 2018;Leaché et al. 2019). Refugia where ectotherms have persisted during climate change can often be characterised as heterogeneous landscapes, in terms of geography, that provide both shelter and an opportunity for the persistence of microclimatic conditions that differ from the surrounding area. ...
Understanding how natural populations will respond to contemporary changes in climate is becoming increasingly urgent and of fundamental importance for the preservation of future biodiversity. Among vertebrates, amphibians and reptiles are more sensitive to environmental perturbations than endotherms and ectotherm diversity will likely be disproportionally impacted by climate change. Notwithstanding concerns surrounding the climate change resilience of ectotherm populations, accurately predicting future population trajectories based on contemporary ecological and physiological data alone remains challenging and much can be learnt by studying how populations have responded to climate change in the past. Genomic approaches can now assay the genetic diversity of contemporary population at an unprecedented scale but to date have been relatively underutilised when studying the demographic history of amphibians and reptiles. In this review, we first summarise how changing climatic conditions may influence the ectotherm phenotype and how this can translate to changes in fitness and population dynamics. We then discuss how the relative role of past climate in shaping ectotherm diversity has traditionally been approached in a phylogeographic context and how expanding genomic resources for ectotherm species can be leveraged to improve the study of past demography for many amphibian and reptilian groups. An integrative approach that links known proximate effects on phenotype due to climate change, with past changes in demographic trajectories will ultimately enable us to generate more accurate models of future population change and improve our ability to assess climate change resilience for many ectotherm groups.
... These include freshwater fish in post-glacial lakes (Hudson et al., 2011) and on Sundaland island archipelagos (Sholihah et al., 2021), birds in boreal North America (Weir & Schluter, 2004) and temperate coastal regions of New Zealand (Weir et al., 2016), grasshoppers in western North American montane sky islands in the Rockies (Knowles, 2000), mangroves in south-east Asia (He et al., 2019), the radiation of annual plants of Nigella across the Aegean archipelago in the Mediterranean (Comes et al., 2008), the rapid diversification of a section of Trigonostemon in the Malay Peninsula and Borneo (Yu & Van Welzen, 2020) and plants in the high elevation Andes (Nevado et al., 2018) and the high Arctic (Brochmann et al., 2004). While a role for Late Pleistocene glacial cycles in species diversification has long been suggested (Haffer, 1969;Simpson, 1974), the impacts of these cycles in different geological settings are likely to be variable and location specific and remain poorly understood (Haffer, 1969;Hewitt, 1996;Klicka & Zink, 1997;Papadopoulou & Knowles, 2015a, 2015bRull, 2011;Weir et al., 2016). ...
... in regions that lack the accentuated island or mountain range topography that generates cycles of flickering connectivity. In flatter areas with less accentuated topography, episodes of isolation and gene flow could still result from cycles of range expansion and migration associated the emergence of land when sea level was low and subsequent contraction as land became covered with water at sea-level maxima, or from cycles of north-south advance and retreat to glacial refugia (Hewitt, 1996). However, whether climatic oscillations in these systems could still drive diversification remains unclear. ...
The importance and prevalence of recent ice‐age and post‐glacial speciation and species diversification during the Pleistocene across many organismal groups and physiographic settings are well established. However, the extent to which Pleistocene diversification can be attributed to climatic oscillations and their effects on distribution ranges and population structure remains debatable. In this study, we use morphologic, geographic and genetic (RADseq) data to document Pleistocene speciation and intra‐specific diversification of the unifoliolate‐leaved clade of Florida Lupinus , a small group of species largely restricted to inland and coastal sand ridges across the Florida peninsula and panhandle. Phylogenetic and demographic analyses alongside morphological and geographic evidence suggest that recent speciation and intra‐specific divergence within this clade were driven by a combination of non‐adaptive allopatric divergence caused by edaphic niche conservatism and opportunities presented by the emergence of new post‐glacial sand ridge habitats. These results highlight the central importance of even modest geographic isolation and short periods of allopatric divergence following range expansion in the emergence of new taxa and add to the growing evidence that Pleistocene climatic oscillations may contribute to rapid diversification in a myriad of physiographic settings. Furthermore, our results shed new light on long‐standing taxonomic debate surrounding the number of species in the Florida unifoliate Lupinus clade providing support for recognition of five species and a set of intra‐specific variants. The important conservation implications for the narrowly restricted, highly endangered species Lupinus aridorum , which we show to be genetically distinct from its sister species Lupinus westianus , are discussed.
... Reconstructing the Evolutionary History of Rock Doves Through a Hypothetical Scenario based on the Refugia Theory It has been proposed that the rock dove's geographic origin is in Asia based on the geographic distribution of its closest species, C. rupestris (Johnston and Janiga 1995). Therefore, Global climate fluctuations during the Pleistocene glacial periods produced drastic changes in the distribution and abundance of flora and fauna, leading to fragmented species distributions, population reductions, high extinction rates, and speciation events (Mayr and O'Hara 1986;Hewitt 1996;Le Houérou 1997;Hewitt 2000;Weir and Schluter 2004;Lovette 2005;Nadachowska-Brzyska et al. 2015). Since the Pleistocene, the Sahara and Sahel underwent several dry and wet cycles associated with the glacial and interglacial periods (Le Houérou 1997;Larrasoaña et al. 2013;Manning and Timpson 2014), with an estimate of 8 to 10 arid-wet periods during the last 125,000 yr alone (Le Houérou 1997). ...
... It has been proposed that during interglacial periods, rapid expansions in northern populations would produce increased homozygosity or low genomic diversity due to founder effects and continuous bottlenecks. In contrast, southern populations in more stable habitats tend to diverge by repeated allopatry during several glacial cycles and by being protected by hybrid zones (Hewitt 1996(Hewitt , 2000, as could be the case of West African rock doves. Refugia theory predicts the establishment of a secondary contact zone after the expansion allopatric populations and the development of hybrid zones (Mayr and O'Hara 1986). ...
The domestic pigeon's exceptional phenotypic diversity was key in developing Darwin's Theory of Evolution and establishing the concept of artificial selection. However, unlike its domestic counterpart, its wild progenitor, the rock dove Columba livia, has received considerably less attention. Therefore, questions regarding its domestication, evolution, taxonomy, and conservation status remain unresolved. We generated whole-genome sequencing data from 65 historical rock doves that represent all currently recognised subspecies and span the species’ original geographic distribution. Our dataset includes three specimens from Darwin's collection, and the type specimens of five different taxa. We characterised their population structure, genomic diversity, and gene-flow patterns. Our results show the West African subspecies C. l. gymnocyclus is basal to rock doves and domestic pigeons, and suggest gene-flow between the rock dove's sister species C. rupestris and the ancestor of rock doves after its split from West African populations. These genomes allowed us to propose a model for the evolution of the rock dove in light of the refugia theory. We propose that rock dove genetic diversity and introgression patterns derive from a history of allopatric cycles and dispersion waves during the Quaternary glacial and interglacial periods. To explore the rock dove domestication history, we combined our new dataset with available genomes from domestic pigeons. Our results point to at least one domestication event in the Levant that gave rise to all domestic breeds analysed in this study. Finally, we propose a species-level taxonomic arrangement to reflect the evolutionary history of the West African rock dove populations.
... Likewise, for areas associated with climate-induced distributional shifts, it is unclear that the extent to the consequences of such shifts for patterns of genetic divergence can be generalized across taxa. For example, while there is evidence that shifting species distributions (e.g., Knowles & Massatti, 2017;Marske et al., 2020) and/or species persistence along ice sheet margins or within glacial refugia (e.g., Bemmels et al., 2019;Çıplak, 2008;Hampe & Petit, 2005;Hewitt, 1996;Ortego & Knowles, 2022) might have promoted genetic divergence, the effects of such factors can be species-specific, complicating generalizations about any particular region (see Çıplak et al., 2015;Chobanov et al., 2017;Kaya & Çıplak, 2016Massatti & Knowles, 2016;Papadopoulou & Knowles, 2016;Uluar et al., 2023;reviewed in McGaughran et al., 2022). ...
... 52 0 latitude; see Hewitt, 2000). However, as we discuss below, range shift dynamics of the PB group seem to be considerably different than proposed hypotheses of a stable rear/leading edge population (Çıplak, 2004b;Hampe & Petit, 2005;Hewitt, 1996;Uluar et al., 2023). Based on the geography and timing of divergence, we develop hypotheses about the joint role of climate-induced distributional shifts and ephemeral barriers in the structuring of the PB group diversification. ...
The complex and dynamic history of the Anatolian Peninsula during the Pleistocene set the stage for species diversification. However, the evolutionary history of biodiversity in the region is shrouded by the challenges of studying species divergence in the recent, dynamic past. Here, we study the Poecilimon bosphoricus (PB) species group to understand how the bush crickets' diversification and the regions' complex history are coupled. Specifically , using sequences of two mitochondrial and two nuclear gene segments from over 500 individuals for a comprehensive set of taxa with extensive geographic sampling, we infer the phylogenetic and geographic setting of species divergence. In addition, we use the molecular data to examine hypothesized species boundaries that were defined morphologically. Our analyses of the timing of divergence confirm the recent origin of the PB complex, indicating its diversification coincided with the dynamic geology and climate of the Pleistocene. Moreover, the geography of divergence suggests a history of fragmentation followed by admixture of populations, suggestive of a ring species. However, the evolutionary history based on genetic divergence conflicts with morphologically defined species boundaries raising the prospects that incipient species divergences may be relatively ephemeral. As such, the morphological differences observed in the PB complex may not to be sufficient to have prevented homogenizing gene flow in the past. Alternatively, with the recent origin of the complex, the lack of time for lineage sorting may underlie the discord between morphological species boundaries and genetic differentiation. Under either hypothesis, geography-not taxonomy-is the best predictor of genetic divergence.
... First, population growth and colonization can occur without recording a genetic signature if ancestral genetic diversity is maintained during expansion. If geographic colonization proceeds gradually via many short-distance dispersal events along the leading edge of a species distribution (phalanx dispersal ;Hewitt 1996), the pool of diversity found in the source population is retained within the newly established range, and coalescent-based methods of demographic reconstruction will infer stable effective population size through time. This contrasts with colonization via long-distance dispersal by a small number of individuals (pioneer dispersal; Hewitt 1996), which causes serial bottlenecking, loss of diversity, and ultimately a clearer genetic signature of demographic expansion. ...
... If geographic colonization proceeds gradually via many short-distance dispersal events along the leading edge of a species distribution (phalanx dispersal ;Hewitt 1996), the pool of diversity found in the source population is retained within the newly established range, and coalescent-based methods of demographic reconstruction will infer stable effective population size through time. This contrasts with colonization via long-distance dispersal by a small number of individuals (pioneer dispersal; Hewitt 1996), which causes serial bottlenecking, loss of diversity, and ultimately a clearer genetic signature of demographic expansion. Shorttailed shrews do not undergo long-distance dispersal, so our demographic results may reflect a history of gradual range expansion that permitted genetic variation to be maintained at stable levels through glacial/interglacial transitions. ...
Across eastern North America, glacial cycles of the Pleistocene drove episodic latitudinal range shifts by temperate species. Isolation of populations within low-latitude refugia during glacial maxima was enhanced by physiographic barriers, leading to patterns of phylogeographic differentiation that are shared across diverse taxa. Postglacial population expansion created opportunities for differentiated lineages to come into contact, with various potential population-genetic outcomes. Northern short-tailed shrews (Blarina brevicauda) exhibit three mitochondrial phylogroups that probably originated via glacial-age range restriction and isolation. We investigate the history of postglacial expansion and interlineage contact between historically isolated regional populations of B. brevicauda. Morphological differences between skulls of shrews representing a Western lineage and those representing Central and Eastern lineages are consistent with past subspecies delineations. However, we demonstrate broad range overlap between neighboring phylogroups across the Upper Peninsula and Lower Peninsula in Michigan. Further, incongruence between phylogroup association and morphology among individuals in Upper Peninsula populations suggests that genetic admixture between shrews representing the Western and Central groups has occurred in the past and may be ongoing. We show that across most cranial measurements, shrews within the contact zone are morphologically most similar to the Central group regardless of mitochondrial identity, but one measurement in these contact zone shrews (depth of skull) is more similar to that seen in the Western group. These results suggest that hybridization between historically isolated populations has resulted in the origin of a novel skull phenotype that is proportionally deeper, narrower, and shorter than those seen in core Western and Central populations.
... Glaciation shifted habitats and sometimes left habitat refugia (Webb and Bartlein 1992). This created opportunity for geographic isolation of populations and the instigation of allopatric speciation as has been hypothesized for many plants and animals (e.g., Hewitt 1996). Pseudips mexicanus/P. ...
Pseudips Cognato, 2000 species are distributed in the western mountains of China and in western North America where
they feed and complete their life cycle under the bark of spruce and pine trees (Pinaceae: Picea and Pinus spp.). The phylogenetic
relationships of the three previously recognized species are as follows: Pseudips orientalis (Wood and Yin, 1986)
is sister to a monophyletic group consisting of Pseudips concinnus (Mannerheim, 1852) and Pseudips mexicanus (Hopkins,
1905). Morphological variation has been observed among some populations which has challenged species boundaries. We
conducted a review of morphological characters and reconstructed a DNA-based phylogeny of individuals from multiple,
widely disjunct locations to test the limits of the three species. A mostly resolved DNA-based phylogeny demonstrated
reciprocal monophyly for Canadian/US and Mexican populations, no overlap of inter- and intraspecific pairwise COI DNA
sequence differences, and corroborated diagnostic morphological characters. In addition, >10% COI DNA sequence difference
as well as diagnostic morphological characters were observed between P. orientalis individuals from Tibet and Qinghai,
China. As a result, Pseudips radiatae (Hopkins, 1915), status restored is resurrected from synonymy with P. mexicanus
and Pseudips yak Cognato and Smith, new species is described. Potential prehistoric environmental scenarios contributing
to Pseudips speciation are discussed.
... Hence, the Y confirmed the hypothesis of their isolation by the Laurentide ice sheet (Hewitt, 1996;Yannic et al., 2014). However, the split time of the two Y clades was estimated around 40 ± 6.1 kya which is substantially younger than the 110 kya split time calculated from autosomal (Wu et al., 2024) and the 70kya calculated for the split of mtDNA clades (Hold et al., 2024). ...
Reindeer, called caribou in North America, has a circumpolar distribution and all extant populations belong to the same species (Rangifer tarandus). It has survived the Holocene thanks to its immense adaptability and successful coexistence with humans in different forms of hunting and herding cultures. Here, we examine the paternal and maternal history of Rangifer based on robust Y‐chromosomal and mitochondrial DNA (mtDNA) trees representing Eurasian tundra reindeer, Finnish forest reindeer, Svalbard reindeer, Alaska tundra caribou, and woodland caribou. We first assembled Y‐chromosomal contigs, representing 1.3 Mb of single‐copy Y regions. Based on 545 Y‐chromosomal and 458 mtDNA SNPs defined in 55 males, maximum parsimony trees were created. We observed two well separated clades in both phylogenies: the “EuroBeringian clade” formed by animals from Arctic Islands, Eurasia, and a few from North America and the “North American clade” formed only by caribou from North America. The time calibrated Y tree revealed an expansion and dispersal of lineages across continents after the Last Glacial Maximum. We show for the first time unique paternal lineages in Svalbard reindeer and Finnish forest reindeer and reveal a circumscribed Y haplogroup in Fennoscandian tundra reindeer. The Y chromosome in domesticated reindeer is markedly diverse indicating that several male lineages have undergone domestication and less intensive selection on males. This study places R. tarandus onto the list of species with resolved Y and mtDNA phylogenies and builds the basis for studies of the distribution and origin of paternal and maternal lineages in the future.
... We can turn to genetic studies to complement what we understand 75 from these other two fields of study. We expect to observe genetic legacies of re-colonization events in 76 modern populations (Hewitt 1996(Hewitt , 2000. These legacies may influence modern populations, and 77 understanding them will be important for evidence-based conservation and management. ...
The Fraser River once supported massive salmon returns, but now years with half of the recorded historical maximum are considered good. There is substantial interest from surrounding communities, governments, and other groups to increase salmon returns for both human use and for functional ecosystems. To help generate resources for this endeavour, we resequenced hundreds of genomes at moderate coverage (~16x) of Chinook ( Oncorhynchus tshawytscha ), coho ( O. kisutch ), and sockeye salmon ( O. nerka ) from the Fraser River. The resequenced genomes are an important resource that can give us new insights. In this study, we found evidence that Chinook salmon have 1.5-2x more polymorphic loci than coho or sockeye salmon. Using principal component analysis (PCA) and admixture analysis, we also identified genetic groups similar to those previously identified with only a few microsatellite markers. As the higher density data supports these previous genetic groups, it suggests that the identity of these groups is not overly sensitive to the number of genetic markers or when the groups were sampled. With the increased resolution from resequenced genomes, we were able to further identify factors influencing these genetic groups, including isolation-by-distance, migration barriers, recolonization from different glacial refugia, and environmental factors like precipitation. We were also able to identify 20 potentially adaptive loci among the genetic groups by analyzing runs of homozygosity. All of the resequenced genomes have been submitted to a public database where they can be used as a reference for the contemporary genomics of Fraser River salmon.
... Every species has its own recolonization rate, influenced by many factors. Location of refugia, ecological niche, dispersal ability, geographical pattern of suitable habitats, and other evolutionary processes like hybridization or polyploidization modify the recolonization rate and slow down the range-filling completion [15][16][17][18]. Hybrid zones can arise between two closely related but previously isolated species that merge their marginal ranges during the process of recolonization in a secondary contact zone. ...
Pleistocene climate oscillations influenced the biogeographical history of most species. In the European Alps, mountain plants were restricted to refugial areas during cold phases of glacial cycles and recolonized newly available habitats during warm periods. The current ranges of alpine plants represent a transient stage of a continuous and dynamic recolonization process that started after the last glaciations. Differences in recolonization rate and range filling are observed between different mountain plant species, but the reasons remain insufficiently explored. Here, we investigated the effects of secondary contact hybridization on range expansion between two related willow species pairs that came into secondary contact. RAD sequencing data was used to identify potential refugial areas and characterize the secondary contact zones. Leaf phenotypes were measured using morphometrics. Distribution modeling was used to find current suitable habitats. Results suggests that peripheral glacial refugia played a major role in the history of the species. For both species’ pairs, the secondary contact zones showed homoploid hybridization between parents, which is also supported by the morphometric analyses. The hybrid zones are broader than expected and characterized by introgression. Current projections of species distribution identified suitable habitats beyond the secondary contact zone. We suggest that the parents’ range expansion is blocked by the hybrid zones. Indeed, due to the high genetic similarity, each dispersal beyond the secondary contact zone results in the long term in hybridization and introgression with the already established parent. Therefore, hybridization acts here as a barrier to further recolonization.
... In the last 420000 years of the history of the Earth alone, four long-term coolings are known (each lasting from 70000 to 110 000 years) (Petit et al., 1999). During the periods of glaciation, the ranges of many species in temperate regions of Europe were reduced and fragmented (Hewitt, 1996). The same processes took place in Asia. ...
An overview of the studies on the sets of chromosomes in Palaearctic mammals is presented, conducted by Russian karyologists who have made important contributions to the improvement of mammalian taxonomy. As for many mammalian species the process of speciation could have been associated with variability in the number and morphology of chromosomes, karyotypes are often used as diagnostic features of morphologically similar cryptic species (twin species). The prospects of cytogenetic research in the field of speciation are discussed, in particular, the selection-based reinforcement of reproductive isolation initiated by chromosomal rearrangements.
... These factors influenced species' ranges: during the shorter warm stages of the Quaternary, warm-adapted species expanded from Mediterranean peninsulas or other spatially restricted areas (refugia), while cold-adapted species retreated uphill and northwards (de Lattin, 1967;Hewitt, 1996Hewitt, , 1999Schmitt, 2007;Schmitt & Varga, 2012). Simultaneously, continental species tended to retreat eastwards (Stewart et al., 2010). ...
Aim
The distribution of within-species lineages has been affected by Quaternary climate changes, and population differentiation has been influenced by species life history traits. We investigated whether the distribution of individual mitochondrial genetic lineages reflects the constituent species' traits. Using the functionally diverse group of butterflies, we examined which lineages are present in Central Europe, an important suture zone.
Location
Czech Republic and Western Palearctic.
Taxon
A total of 140 butterfly species.
Methods
We sequenced DNA barcodes (cytochrome c oxidase 1) (959 sequences) of the entire Czech Republic butterfly fauna and used Barcoding of Life Data System to visualise the species' biogeographic patterns across Europe. We categorised the distribution patterns of lineages inhabiting the Czech Republic, and used multivariate statistics to interpret these categories by the butterflies' habitats, life history traits and threat levels.
Results
Open habitat dwellers with specialist traits belonged to Eastern, Southern and temperate lineages. Habitat generalists and woodland dwellers belonged to the Western lineage, formed several lineages or displayed low genetic diversity; they often developed on woody plants, were large-winged and had long flight periods. The most threatened species were the specialists of Southern, Eastern and temperate lineages.
Main Conclusions
The distribution of lineages in Central Europe reflects the history of Quaternary ecosystems: during cold periods of the Pleistocene, the diverse open habitats prevailed and species could expand westwards. Such species also suffer the most under the current anthropogenic habitat alteration. On the other hand, the mobile generalists and woodland dwellers expanded to Central Europe during the Holocene. Our approach of linking the distribution of lineages with species traits can be transferred to other study systems, and we show that DNA barcoding of under-sampled areas represents a powerful tool for discovering the driving forces of biogeography.
... Bayesian skyline plot indicated that M. nipponense populations in the TGR began to shrink 700 years ago, which may be related to the Little Ice Age that began in the 13th century and ended in the early 20th century (Zhu, 1973). The Earth's climate alternates between ice ages and warm periods, with aquatic organisms generally experiencing population contraction or bottlenecking during colder ice ages and population expansion during warmer interglacial periods (Hewitt, 2000(Hewitt, , 1996Li 2015). The Little Ice Age is the nearest ice age, and the average temperature during it was approximately 1-2°C lower than present temperature, even in some places the minimum temperature may be 5-7°C lower than the modern, which may have contributed to the contraction of M. nipponense populations in the TGR (Chang et al., 2020;Zhou et al., 2019;Zhu, 1973). ...
Macrobrachium nipponense is a major farmed species freshwater shrimp in China and its genetic diversity is of high value in aquaculture. The construction of the Three Gorges Project has slowed down the water velocity in the Three Gorges Reservoir (TGR) and made the water more clear, which is more favourable for the survival and reproduction of M. nipponense. However, there are lack of studies on the genetic diversity of M. nipponense populations in the TGR. In this study, mitochondrial COI gene sequences were used as molecular marker to analyze the genetic diversity, genetic differentiation and historical demography of eight M. nipponense populations in the TGR. The results showed that the M. nipponense populations in TGR have high genetic diversity. There was some genetic differentiation between the four populations in lower reaches of the TGR and four populations in the upper reaches of the TGR. We also found that there was a significant correlation between genetic distance and geographical distance among the M. nipponense populations in the TGR. The M. nipponense population in the TGR has experienced population reduction in the recent year, which might be related to the ice age movement in the Little Ice Age and human activities. This study provides a theoretical basis for the rational development and protection of M. nipponense resources in the TGR.
... Here we examined if there were concordant patterns of genetic structure for these three species of goatfish across this purported environmentally heterogeneous region. Comparative phylogeography has been used in many terrestrial and freshwater environments for delimiting regional phylogeographic patterns (Avise, 1996;Bowen et al., 2016;Hewitt, 1996). We focused on three goatfish species from two different genera to assess their genetic structure in the Nile Delta's unique environment at the Mediterranean Sea's periphery in Egypt. ...
... Much of the increase in documented species richness is in the southern Holarctic -thus more in Iberia than in Siberia -in line with the well understood 'southern richness, northern purity' paradigm (Hewitt, 1996(Hewitt, , 2000. The present study follows on from analyses that deal with morphological and genetic differentiation of large-bodied newts (genus Triturus) in southwestern Europe, i.e., France, Spain and Portugal (Arntzen, 2018(Arntzen, , 2024. ...
Iberian populations of large-bodied newts, with Triturus marmoratus in the north and T. pygmaeus in the south of the peninsula, were studied for external morphology, mitochondrial dna and for a panel of single nucleotide polymorphisms. This confirmed the species’ low level of interspecific hybridization and their parapatric, mosaic-like mutual range border across the peninsula. The genetic data also revealed substantial variation within T. pygmaeus , with narrow (0.43–35.2 km) clinal transitions in the very centre of Portugal. Similar clines were observed for body size and colouration pattern. Pygmy newts in the west of Portugal are larger, with a more striped (less reticulated) green dorso-lateral colouration pattern than those in the east and south of the country. The western group of populations is described as a new species, Triturus rudolfi sp. nov. , on account of a long, ca. 2.5 Ma, independent evolutionary history and limited hybridization with its sister-species T. pygmaeus , suggesting selection against hybrid offspring. The range of the newly described species may be restricted to the wider Lisbon Peninsula, stretching northwards along the Atlantic coast to the river Vouga estuary. Inland, the range border may be set by the lower Tejo River, or by the currently wide area of agricultural land at either side of that river, that may accommodate a residual hybrid zone. The close contact between both pygmy newt species is effectively limited to a ca. 20 × 40 km area directly north of the town Entroncamento, where T. rudolfi sp. nov. is sandwiched in between T. marmoratus and the river Tejo.
... Zhang & Sun, 2011). And the repeated alternating cycles of population contraction during the ice age and expansion after the ice age became the dominant pattern for many plants in the Northern Hemisphere, enabling their survival throughout the Quaternary ice age(Godfrey M. Hewitt, 1996). On the QTP and ITS adjacent areas, the HHM region in the southeastern part of the QTP may have served as an important refuge for endemic species during the ice age, thanks toITS distinctive mountainous topography(Q. ...
Exploring the geological events and climate change in the Himalaya-Hengduan Mountains (HHM) region and the Qinghai-Tibet Plateau (QTP) is crucial for understanding the impact of environmental change on biogeographic distribution and biological evolution. To delve deeper into these mechanisms, we reconstructed the evolutionary history of three Notholirion species that span these regions. Here, we examined a total of 254 individuals from 31 populations of these three species, utilizing five chloroplast DNA (cpDNA) (matK, ndhA, ndhG-ndhI, petB-petD, and petL-petG), along with one nuclear DNA region (internal transcribed spacer, ITS). We identified 14 haplotypes from cpDNA and 27 haplotypes from the ITS, each specific to corresponding species. Robust haplotype trees were detected, and obvious discrepancies were found between the cpDNA and ITS trees. A total of 147 chloroplast genomes were used for divergence time estimation, of which 10 chloroplast genomes from distinct populations of Notholirion species provided a comprehensive representation of the genus. The divergence time estimation results suggested that species of Notholirion genus originated in the southern Himalayan region during the Late Oligocene period (25.05 Ma), and the three Notholirion species then diverged during the Late Pliocene period (7.43 Ma). Our maximum model forecasts that the overall distribution range of Notholirion over four different periods remains relatively stable，from LIG to the future. The origin of the genus Notholirion was triggered by sustained climate fluctuations during the Late Oligocene, with the uplift of the Himalayas and the subsequent orogenic movements intensifying climate changes and further promoting the species divergence of Notholirion. A long evolutionary history, coupled with sexual reproduction and habitat fragmentation, likely contributed to the higher genetic diversity of Notholirion. The higher genetic differentiation among Notholirion populations may be attributed to drastic changes in the external environment within their range, as well as their constrained capacity for seed production and dispersal.
... Low Streptom yces cultur able species div ersity fr om these Himalayan r anges may be attributed to the low temper atur es, oligotr ophy, dispersal limitation and glaciated soils of these sampling sites . T he microclimate ice cold temper atur es and historical patterns of glaciations in Himalaya and adjacent mountains might have limited the time for Streptomyces speciation, decreased the phylogenetic diversity and increased the phylogenetic clustering of this genus (Hewitt 1996 ). Phylogenetic clustering of NWH and species commonness among different sites may be attributed to their equitable ecological and climate conditions, with almost all the sites bearing a similar climate and v egetation patterns. ...
The increasing global concern of antimicrobial resistance and shortage of new antimicrobials necessitates exploring untapped terrestrial environments for new bioactive microbiome diversity. The low temperature and oligotrophic North Western Himalaya (NWH) region has a vast diversity of Streptomyces with potential antimicrobial properties that remain largely unexplored. This study evaluates the diversity of culturable Streptomyces from high altitude NWH and their potential as a source of new antimicrobials through genus specific isolation and identification. The results demonstrate a distinct phylogenetic clustering of Streptomyces from different sampling regions of NWH, site-specific variation in culturable β-diversity and species commonness with varying inter site bioactivity among different sites. Further, the study optimized the media selection for large-scale culture cultivation in antibiotic production processes and demonstrated the antimicrobial efficacy of Streptomyces against a range of pathogens through in-vitro bioassays using minimum inhibitory concentration (MIC) determination and antibiofilm activity. Untargeted label-free proteomic profiling also revealed variable expression of stress response proteins and antibiotic regulators as a competitive survival strategy for selective antagonistic Streptomyces. The findings highlight the potential of NWH in augmenting antimicrobial discovery and combating antimicrobial resistance through the isolation and study of novel bioactive Streptomyces.
... OLE + OLC, OTM + OTL) experienced rapid expansion after glaciation, whereas single Taiwan or single mainland taxa failed to exhibit such expansions ( Figure 5). It seems clear that the Quaternary glaciation strongly influenced the distribution and genetic patterning of these emergent species (Hewitt, 1996(Hewitt, , 2000. ...
Biotic exchanges between Taiwan and Mainland China have shaped the biodiversity and ecosystems of both regions. Exchanges from Mainland China to Taiwan have received more attention, mainly studied in terrestrial vertebrates, while the reverse direction and invertebrates have largely been overlooked. Here, we explore the dispersal events between these two regions based on the moths of three species groups of Obeidia , including Taiwan taxa and its relatives from mainland. We conducted mixed methods and analysis, including reconstructing a phylogenetic tree, estimating associated divergence times and inferring ancestral areas and source regions, to explore the phylogeographical structure and genetic pattern of three groups based on eight genes. Our results revealed a structure of three clades and every clade included at least one Taiwanese taxa and its closest relatives of mainland of China, and also served Taiwan as an important source region of two mainland taxa. Our study revealed various origin pattern and dispersal models on the basis of three species groups of Obeidia . Bi‐directional biotic exchange via a land bridge were found: four Taiwanese taxa originated from mainland, and two of them migrated back to mainland. Both eastern Himalayas and south China are important origin areas for Taiwan biota, and the dominant source region may need multiple insect cases to confirm. Our study also provided evidences for disjunct distribution from the perspective of insecta molecular phylogeny.
... In light of the results from our study, the haplotype diversity of the idle crayfish population is now similar in genetic diversity to those endemic lineages of Austropotamobius in the Dinarides (Lovrenčić et al., 2020). This aspect highlights the role of karst as a refuge during the Pleistocene glaciations, which had a general reducing effect on biodiversity due to multiple oscillations between warm and cold conditions (Hewitt, 1996), but somehow, the idle crayfish coped with maintaining viable populations on karst . ...
Knowledge about the conservation status of a species is crucial for its protection in the long run. It provides insights into the geographic range, population size and trend, which are useful in management activities towards safeguarding the future of a species. The idle crayfish, Austropotamobius bihariensis, is a recently described crayfish species that has not yet undergone a full conservation assessment. Here, we present our extensive 13-year study that aimed to fill this gap by investigating and monitoring the species' entire geographic occurrence range and quantifying its subpopulations. Although it is an endemic crayfish located in the Apuseni Mountains (Romania), its range and population is stable. The observed relative abundance is highly unbalanced within subpopulations, with 71% falling below ten individuals per 100 m river stretch. We documented four extinct subpopulations (ca. 16%), whereas more than half of the subpopulations being in a size-decreasing trend. Since no invasive crayfish were detected in (or very close to) its distribution area, the idle crayfish can still be considered safe against invasions. However, based on our findings and following the IUCN Red List Guidelines, we concluded that idle crayfish's most appropriate conservation status is Endangered. IUCN ratification is required for increased significance.
... Pleistocene glaciations are one of the most important historical climatic events explaining the current distribution of species in Europe (Hewitt, 1996(Hewitt, , 2000. During this period, northern Europe was covered by ice sheets, and most of the fauna and flora were restricted to glacial refugia, mainly in the Mediterranean region (Hewitt, 1999). ...
Aim
To assess the relative relevance of dispersal limitation and species sorting as drivers of spatial turnover between spider faunas of European territories.
Location
Continental Europe.
Time period
Present.
Major taxa studied
Spiders (Order Araneae).
Methods
We analysed how distance‐decay patterns differ between northern and southern Europe (broadly, territories covered vs. not covered by ice sheets during the last glacial maximum, respectively) in 15 spider families, using standardized distances to allow a direct comparison between parameters (i.e. slope and intercept) of climatic and spatial distance‐decay models. Thus, we assessed North–South differences in parameters of spatial and, independently, climatic distance‐decay models, and whether those differences are explained by family‐specific traits related to dispersal ability.
Results
Climatic and spatial distance‐decay patterns are very similar in northern Europe, where climatic and spatial distances are highly correlated. In contrast, slopes are steeper in spatial than in climatic distance‐decay curves in southern Europe, where climatic and spatial distances are decoupled. Moreover, family traits related to dispersal ability explained the North–South difference in spatial distance‐decay slopes, as well as the amount of nestedness‐resultant dissimilarity between southern and northern spider faunas.
Main conclusions
Our results suggest that differences in beta diversity patterns between northern and southern Europe reflect the strength of dispersal limitation in spiders, which varies across families and leads to different degrees of disequilibrium with current climatic conditions depending on the taxon. Moreover, in the South of Europe, where spatial and climatic distances are uncorrelated, spatial distance‐decay models are steeper and have larger explanatory power than climatic distance‐decay models, which suggests that dispersal limitation is the main factor shaping current beta diversity patterns of European spiders at the continental scale.
... In a heterogeneous fitness landscape, this high genetic diversity would provide a greater adaptive potential and promote divergence under environment-specific selection (Hamrick & Godt, 1996;Savolainen et al., 2013;Gamba & Muchhala, 2020). Consecutive range expansions after contraction may carry only a portion of the diversity from the source population and produce differentiation via genetic drift (Hewitt, 1996;Orsini et al., 2013;Wang & Bradburd, 2014;Zhao et al., 2020). These processes could potentially constrain a species ability to track, tolerate and adapt to changing environments through their impact on standing adaptive genetic diversity or on gene flow between populations. ...
Scots pine is the foundation species of diverse forested ecosystems across Eurasia and displays remarkable ecological breadth, occurring in environments ranging from temperate rainforests to arid tundra margins. Such expansive distributions can be favored by various demographic and adaptive processes and the interactions between them.
To understand the impact of neutral and selective forces on genetic structure in Scots pine, we conducted range‐wide population genetic analyses on 2321 trees from 202 populations using genotyping‐by‐sequencing, reconstructed the recent demography of the species and examined signals of genetic adaptation.
We found a high and uniform genetic diversity across the entire range (global F ST 0.048), no increased genetic load in expanding populations and minor impact of the last glacial maximum on historical population sizes. Genetic‐environmental associations identified only a handful of single‐nucleotide polymorphisms significantly linked to environmental gradients.
The results suggest that extensive gene flow is predominantly responsible for the observed genetic patterns in Scots pine. The apparent missing signal of genetic adaptation is likely attributed to the intricate genetic architecture controlling adaptation to multi‐dimensional environments. The panmixia metapopulation of Scots pine offers a good study system for further exploration into how genetic adaptation and plasticity evolve under gene flow and changing environment.
... Additionally, species response to climatic fluctuations may also have an important role in speciation. These oscillations isolate populations in disjunct areas, leading to genetic divergence and ultimately to speciation Amiri et al., 2021;Hewitt, 1996;Tarkhnishvili et al., 2013). Evolutionary diversification rate, extinction, and speciation shape global patterns of biodiversity in different regions (Schluter & Pennell, 2017). ...
Mesalina watsonana is a well-known species of small lacertid lizards with an extensive species distribution that exhibits high genetic diversity. The species has a wide distribution range in Iran, some parts of Turkmenistan, Afghanistan, Pakistan, and northwest India. This study aims to generate phylogenetic and phylogeographic evidence to derive taxonomic recommendations supporting. Furthermore, this species can be used as a model for examining Iranian Platuea's historical biogeography. We conducted a very detailed sampling of its distribution and used genetic approaches. Phylogenetic analyses were done implementing two mitochondrial (Cytb and 16S) and one nuclear (C-mos) gene fragments. Combination of these results indicated that seven well-supported distinct clades exist within this species complex, i.e. Kerman clade, Esfarayen clade, Halil clade, Ardestan clade, M. watsonana clade, Bardaskan Clade, and Khuzestan Clade in Iran. Also, our results revealed that several distinct clades diverged due to geologic events when the Dasht-e-Kavir and the Zagros Mountains were formed. It seems that the ancestor of M. watsonana spread to Iranian Plateau before the formation of the Zagros Mountains. Orogenic activities of the Zagros Mountains and the formation of deserts have influenced the separation of these lineages from the Late Miocene by allopatric speciation. Generally, our findings suggest that each of the seven clades corresponding to distinct geographic regions deserves to be elevated to the species level.
... This would be in agreement with the often-proposed hypothesis that populations of mammals exhibit reduced genetic diversity on recently deglaciated land (e.g. Hewitt, 1996Hewitt, , 2004. The glacial extent in the north and northwestern valleys of the plateau margins persisted until ~16 kya, while the ice shield on the plateau around Tullu Dimtu was smaller in extent already ~20 kya (Groos et al., 2021). ...
Due to their limited dispersal ability, fossorial species with predominantly belowground activity usually show increased levels of population subdivision across relatively small spatial scales. This may be exacerbated in harsh mountain ecosystems, where landscape geomorphology limits species' dispersal ability and leads to small effective population sizes, making species relatively vulnerable to environmental change. To better understand the environmental drivers of species' population subdivision in remote mountain ecosystems, particularly in understudied high‐elevation systems in Africa, we studied the giant root‐rat ( Tachyoryctes macrocephalus ), a fossorial rodent confined to the afro‐alpine ecosystem of the Bale Mountains in Ethiopia. Using mitochondrial and low‐coverage nuclear genomes, we investigated 77 giant root‐rat individuals sampled from nine localities across its entire ~1000 km ² range. Our data revealed a distinct division into a northern and southern group, with no signs of gene flow, and higher nuclear genetic diversity in the south. Landscape genetic analyses of the mitochondrial and nuclear genomes indicated that population subdivision was driven by slope and elevation differences of up to 500 m across escarpments separating the north and south, potentially reinforced by glaciation of the south during the Late Pleistocene (~42,000–16,000 years ago). Despite this landscape‐scale subdivision between the north and south, weak geographic structuring of sampling localities within regions indicated gene flow across distances of at least 16 km at the local scale, suggesting high, aboveground mobility for relatively long distances. Our study highlights that despite the potential for local‐scale gene flow in fossorial species, topographic barriers can result in pronounced genetic subdivision. These factors can reduce genetic variability, which should be considered when developing conservation strategies.
... These results support previous claims that introgression in temperate regions may be common when ranges underwent cyclic alterations during Pleistocene glacial cycles (Folk et al., 2023;Maier et al., 2019). Similar patterns of isolation and secondary contact, driven by glacial cycles, have been observed in various taxa inhabiting the Andes mountain chains (Esquerré et al., 2022;Nevado et al., 2018;Victoriano, 2020) and other high-altitude environments (Colella et al., 2018;Hewitt, 1996;Maier et al., 2019). In this study, we extend these observations to the lowland areas of the Patagonian Steppe. ...
Evolutionary processes behind lineage divergence often involve multidimensional differentiation. However, in the context of recent divergences, the signals exhibited by each dimension may not converge. In such scenarios, incomplete lineage sorting, gene flow, and scarce phenotypic differentiation are pervasive. Here, we integrated genomic (RAD loci of 90 individuals), phenotypic (linear and geometric traits of 823 and 411 individuals, respectively), spatial, and climatic data to reconstruct the evolutionary history of a speciation continuum of liolaemid lizards (Liolaemus kingii group). Specifically, we (i) inferred the population structure of the group and contrasted it with the phenotypic variability; (ii) assessed the role of post-divergence gene flow in shaping phylogeographic and phenotypic patterns; and (iii) explored eco-geographic drivers of diversification across time and space. We inferred eight genomic clusters exhibiting leaky genetic borders coincident with geographic transitions. We also found evidence of post-divergence gene flow resulting in transgressive phenotypic evolution in one species. Predicted ancestral niches unveiled suitable areas in southern and eastern Patagonia during glacial and interglacial periods. Our study underscores integrating different data and model-based approaches to determine the underlying causes of diversification, a challenge faced in the study of recently diverged groups. We also highlight Liolaemus as a model system for phylogeographic and broader evolutionary studies.
... Geographical isolation followed by genetic drift and natural selection may have led to genetic divergence among populations (Hewitt, 1996). It may also facilitate the development of genetic incompatibility and the potential for reproductive isolation and speciation, thus clades identified in phylogeographic studies may correspond to incipient species (Avise et al., 1998;Carstens & Knowles, 2007). ...
Aim
Description of the driving forces for genetic divergence is important for understanding spatial pattern of biodiversity and development of conservation plans. Paleo‐climate, geographical barriers and habitat heterogeneity are considered to be the main influential factors; however, an integrative study is still lacking to reveal their interactions.
Location
Eastern North America.
Methods
Here, we generated MIG‐seq SNPs of 403 Sanguinaria canadensis samples and seven plastome data. The methods of phylogeography and landscape genomics were applied to infer their genetic divergence, demography, species distribution modelling, ecological differentiation and local adaptation.
Results
We identified three distinct genetic lineages corresponding to geographical distributions isolated by the Appalachian Mountains and the Mississippi River. Ecological niche modelling and population demographic inference demonstrated that the response of S. canadensis to Pleistocene climate changes was consistent with the pattern of southward contraction during the ice age and northward recolonization during the inter−/postglacial period. Isolation in multiple southern refugia was a key factor resulting in the genetic divergence, whereas secondary contact triggered by repeated range shifts allowed gene flow among different lineages. A greater effect of isolation‐by‐environment than isolation‐by‐distance was founded, which suggested heterogeneous environment was also a promotor of genetic differentiation. Candidate adaptive loci related to transposable elements were identified under the influence of divergent environmental selection. Ecological niche divergence also reflected adaptation to different environments.
Main Conclusions
This study revealed that genetic divergence has occurred within S. canadensis populations under the combined effect of paleo‐climate, geographical barriers and habitat heterogeneity, and emphasized the necessity of establishing different conservation units in future biological conservation and management work.
... Our understanding of range disjunctions has profoundly improved through the use of molecular methods and phylogenetic analyses (Puşcaş et al., 2021;Ronikier, 2011;Schmitt, 2009;Schönswetter et al., 2003), especially when combined with the fossil record and climate models (Gavin et al., 2014). In the European biota, many range disjunctions have been driven by shifts and pulses in the species distributions in response to Pleistocene climatic oscillations (Hewitt, 1996;Ronikier, 2011;Schmitt, 2007;Schönswetter et al., 2002). Disjunct populations may represent ancient vicariants, and as such they are usually genetically unique, having evolved separately over long periods of time (Collevatti et al., 2009;Cox & Moore, 2005). ...
Aim
Various species distributed in the Alps have their disjunct occurrences in the Carpathians. Fossil evidence for some woodland snails of Alpine distribution suggests that they colonized the Carpathians during the Holocene forest optimum or later. Here, we focus on disjunct Carpathian populations of the rock‐dwelling alpine snail Pyramidula saxatilis . As it occupies very stable habitats, that is, high‐elevation limestone rocks, one can assume its potential survival in Carpathian refugia over the glacial period(s). For comparison, the more widespread and warm‐climate P. pusilla is analysed.
Location
Europe.
Taxon
Pyramidula saxatilis and P. pusilla.
Methods
We analysed the genetic diversity of P. saxatilis and P. pusilla populations across their entire ranges using mitochondrial DNA and nuclear DNA markers. Seven fossil mollusc successions from the area where P. saxatilis occurs in the Carpathians were analysed and dated using the radiocarbon method. Habitat suitability models of both species were calculated for selected time periods since the Last Glacial Maximum.
Results
All Carpathian P. saxatilis populations were genetically homogeneous and similar to those from the Eastern Alps. In P. pusilla , we found a genetically distinct lineage in the southern Western Carpathians. Both species were found in three fossil profiles since the Middle Holocene, and in one already in the Late Glacial. Habitat suitability models suggested the fluctuations of suitable conditions in the Carpathians driven by summer precipitation, especially for P. saxatilis .
Main Conclusions
Our results suggest that the Carpathian populations of P. saxatilis represent a post‐LGM colonization from the Eastern Alps triggered by climatic changes, mainly by the increase in summer precipitation during the Late Glacial interstadials and Middle Holocene. The evidence for P. pusilla is similar, but also suggests rare long‐term survival in the Carpathian microrefugia. The palaeoecological evidence indicates a possible threat to high‐elevation species from future fluctuations in precipitation regimes.
... Sea-level fluctuations have also played a key role in shaping the seascape worldwide, being a potential driver of speciation in marine biota, particularly for species from shallow coastal waters and estuaries (Hewitt 1996;Lambeck and Miller et al. 2005;Grant and Bowen 2006;Jacobina et al. 2020). In Western Atlantic, sea-level fluctuations have also affected the dynamics of the AOP, resulting in significant differences in the sediment distribution during the glacial maxima when sea level was approximately 130 m lower than that presently observed (Rocha et al. 2005). ...
Traditionally, the apparent paucity of biogeographic barriers in marine environments when compared to terrestrial and freshwater habitats has been associated with high gene flow rates among geographically distant populations. However, physical traits such as tide currents, temperature, and salinity levels may serve as ecological boundaries thus leading to restricted-range phylogeographic patterns (e.g., the outflow plume from the Amazonas-Orinoco rivers between the Caribbean and the Brazilian Province) according to adaptive features of coastal organisms. To assess the degree of cohesiveness among populations and species of marine and estuarine fishes along a latitudinal gradient from Western South Atlantic, we carried out comparative phylogenetic and species delimitation analyses based on Cytochrome C Oxidase I (COI) sequences of 34 fish taxa from the Caribbean and Brazilian coasts. Distinct values of genetic diversity were revealed for both Provinces, ranging from moderate (1 to 2%) to high (≥ 2%) in 11.76% and 20.59% of the analyzed taxa, respectively. Furthermore, a significant genetic differentiation was observed within the nominal taxa Diapterus auratus, Citharichthys spilopterus, and Scorpaena plumieri from the Caribbean, as well as for Haemulon plumierii between the Caribbean and Brazilian Provinces. Such divergence is likely to result from temporal isolation among local populations during sea-level fluctuations during the Pliocene-Pleistocene period. The present findings demonstrate that similar biogeographic boundaries may result in species-specific patterns of genetic connectivity, possibly associated with ecological constraints. Since molecular operational taxonomic units (MOTUs) were identified in certain formal taxa from both Provinces, a systematic revision of these groups is highly recommended. At last, multispecies COI data proved to be helpful to phylogeographic inferences and to support appropriate policies for the conservation of natural resources.
... However, I found no difference in the L1 population (Fresh 3 in Gómez-Mestre and Tejedo, 2004) ( Table 4). The lower allelic diversity found in the British populations also supports the hypothesis that the Iberian Peninsula constituted a Pleistocene refuge for E. calamita (as it was for other species in other Mediterranean peninsulas; Hewitt, 1996;Taberlet et al., 1998). From this refuge, the species would have expanded rapidly to north and east during the postglacial stage (Beebee and Rowe, 2000), resulting in a pattern of high levels of genetic diversity in populations derived from southern refuge and a progressive loss of diversity in recolonized areas to the north (Avise, 1994). ...
Population genetic studies are crucial for evolutionary biologists because the population is the basic substrate on which evolution is forged. However little empirical evidence has been able to demonstrate the role that isolation and gene flow play in maintaining differentiation in populations at short geographic scales. Epidalea calamita exhibits a steep variation in body size and reproductive traits in southwestern Spain, associated with changes in the geological substrate. This implies a decrease of 70.9% of body mass and 28.5% in snout-vent length, on a micro-geographic scale of only 60 km. Previous results from both metamorphic and juvenile common garden experiments showed that genetic differentiation may be a causal determinant of geographic variation in adult. This study tested whether neutral genetic differentiation can explain the geographical variation in the body size observed in E. calamita. It was addressed analyzing the level of genetic structuring and gene flow among populations along the cline, comparing the genetic diversity between and within populations, as well as between ecological environments. The study showed that the geographic variation in body size observed in E. calamita has evolved in absence of geographic isolation, with moderate gene flow connecting the populations. Thus, neutral genetic differentiation cannot explain the geographical variation observed. Future studies are needed on the interaction between the genetic component with the environmental factors and will be necessary to analyze the contribution of the maternal effects in the origin and evolution of the geographical variation in the body size observed in E. calamita from southern Spain.
... In other possible cases, e.g., with the multiple previous refugia, at least the spatial factors would show a moderate or more substantial correlation with the genetic traits. We assume that small populations of sand flies migrated to the east after the post-glacial era from the Southwest Ice Age refugium in several waves during the last 6 kys, as also demonstrated for other insect taxa, e.g., grasshoppers (Orthoptera) 63,64 . ...
Phlebotomine sand flies (Diptera: Phlebotominae) are the principal vectors of Leishmania spp. (Kinetoplastida: Trypanosomatidae). In Central Europe, Phlebotomus mascittii is the predominant species, but largely understudied. To better understand factors driving its current distribution, we infer patterns of genetic diversity by testing for signals of population expansion based on two mitochondrial genes and model current and past climate and habitat suitability for seven post-glacial maximum periods, taking 19 climatic variables into account. Consequently, we elucidate their connections by environmental-geographical network analysis. Most analyzed populations share a main haplotype tracing back to a single glacial maximum refuge area on the Mediterranean coasts of South France, which is supported by network analysis. The rapid range expansion of Ph. mascittii likely started in the early mid-Holocene epoch until today and its spread possibly followed two routes. The first one was through northern France to Germany and then Belgium, and the second across the Ligurian coast through present-day Slovenia to Austria, toward the northern Balkans. Here we present a combined approach to reveal glacial refugia and post-glacial spread of Ph. mascittii and observed discrepancies between the modelled and the current known distribution might reveal yet overlooked populations and potential further spread.
... As the climate warmed and glaciers retreated, species with a temperate range of distribution expanded and reconnected. In contrast, the range of distribution for boreal cold-adapted species likely reduced and fragmented (Hewitt, 1996;Petit et al., 2003). Evidence from several ant species have suggested the presence of several refugia during the Pleistocene (2.58-0.012 ...
... When we consider an intraspecific scale, the expected genetic signatures are high genetic diversity in populations occurring in stable areas (named refuges), and low genetic diversity in populations located in regions colonized after climatic shifts during the warm periods (unstable areas). Secondary contact and demographic changes are events that are also observed in this hypothesis (Hewitt 1996). ...
... Fostered by founder effects, this resulted in decreasing genetic variability with increasing distance from the respective refugia. Conversely, southern populations survived the cold periods locally and preserved their ancient genetic diversity (Hewitt, 1996). Palearctic regions of high variation and complexity are the southern peninsulas, from west to east the Iberian, the Apennine and the Balkan peninsula (Schmitt, 2007). ...
Morphological and genetic variation of organisms is generally lower in northern than in southern regions of the Palearctic. This ubiquitous geographical pattern has been associated with extinction and recolonization processes in the north versus persistence in the Mediterranean area, as governed by climate change in the Pleistocene. One area of differentiation and complexity is the Iberian Peninsula where two distinct sister-species of marbled newts possess adjoining and geographically sharply delimited ranges over the north ( Triturus marmoratus ) and the south of the peninsula ( T. pygmaeus ). Within the latter species two forms are here documented, with different colouration patterns and non-overlapping ranges. The southern form is striped, much as in T. marmoratus , and occurs to the south of the Guadalquivir River. The northern form, here described as a new subspecies, has a reticulated dorsal colouration. It occurs only north of the Guadalquivir and is thus sandwiched in between two striped marbled newt taxa. Both T. pygmaeus subspecies engage inside the Doñana National Park in a ca. 2,500 m narrow contact zone. Although an inferred substantial selection against hybrids goes a long way to support species status, a reanalysis of published genetic data is required to solve this issue, along with the wider investigation of the same type of (microsatelite) data for the southern, nominotypical subspecies.
... Fish from previously glaciated basins showed strong genetic differentiation, but they had somewhat lower genetic diversity than fish from unglaciated basins, with significantly lower values of H o and AR ( (Bernatchez & Dodson, 1991;Billington & Hebert, 1991;Haponski & Stepien, 2008;Hewitt, 1996Hewitt, , 2000Luiken et al., 2021;Sepulveda-Villet et al., 2009;Sepulveda-Villet & Stepien, 2012). ...
Freshwater darters belonging to the orangethroat darter species complex, or Ceasia, are widely distributed in the Central and Southern United States, with ranges that span both glaciated and unglaciated regions. Up to 15 species have been recognized in the complex, with one, Etheostoma spectabile, having a widespread northern distribution and another, Etheostoma pulchellum, having a sizeable southern distribution. The other species in the complex have much more restricted distributions in unglaciated regions of the Central Highlands. We sampled 384 darters from 52 sites covering much of the range of Ceasia and evaluated patterns of genetic diversity, genetic structure, and pre‐ and post‐glacial patterns of range contraction and expansion. We anticipated finding much stronger signals of genetic differentiation and diversification in unglaciated regions, given the higher species diversity and levels of endemism reported there. Surprisingly, microsatellite genotyping revealed two well‐differentiated genetic clusters of E. spectabile in samples from glaciated regions, one confined to the Illinois River basin and another found in the Wabash drainage and Great Lakes tributaries. This suggests that there was expansion from two isolated glacial refugia, with little subsequent post‐glacial gene flow. Fish collected from throughout the unglaciated region were less genetically differentiated. Fish assigned to Etheostoma burri and Etheostoma uniporum based on collection sites and morphological characters were not genetically differentiated from E. spectabile samples from the region. Hybridization and introgression occurring in the Central Highlands may confound genetic delineation of species in this region of high endemism and diversity.
... * Yafeng Wen wenyafeng7107@163.com * Yoshihiko Tsumura tsumura.yoshihiko.ke@u.tsukuba.ac.jp increase the genetic differentiation between refuges and even produce new species (Hewitt 1996). With the increase in human activities, human disturbance became a major biotic factor and might have a negative effect on genetic diversity or structure. ...
Genetic structure and distribution patterns of modern floras are strongly affected by climatic change and geographical isolation. In the present study, we applied restriction site associated DNA sequencing (RAD-seq) to analyze the genetic structure and to simulate the demographic history of two extant Cryptomeria species in Japan (C. japonica) and Southeastern China (C. japonica var. sinensis). Thirteen natural populations representing the entire species distributed in East Asia were collected from Japan and China. At the species level, the genetic diversity of Cryptomeria was moderate (Ho = 0.217, He = 0.203) with a significant genetic differentiation among populations (85.30%, P < 0.001), especially between Japan and China lineages (FST = 0.147). Except for the Lushan (LS) population in China, all populations were clustered into two lineages (Japanese and Chinese), which was consistent with their geographical distribution. Approximate Bayesian computations (ABC) model indicated that the current two geographical lineages diverged from a common ancestral lineage, and that their divergence time was about 0.417 ~ 0.139 million years ago (Mya). Geographical isolation, climate change in the Quaternary, and human disturbance played important roles in genetic variation and distribution patterns of Cryptomeria in East Asia. Our results shed light on the speciation processes of Cryptomeria and provide a reference for the conservation of this species.
... Mediterranean mountains are among the primary hotspots of biodiversity in the Western Palearctic (Hewitt, 1996;Cuttelod et al., 2009;Klesser et al., 2021). These mountain ranges shaped diversity and distributions across the region by serving as refugia during Quaternary glaciations Thorell, 1876, recorded from Greece, indicating major areas of occurrence. ...
Mediterranean mountains and Pleistocene glacial cycles are responsible for much of the unique biodiversity of the Western Palearctic, acting respectively as refugia and drivers of diversification. Mount Olympus, a legendary Greek landmark, is a perfect example. This massif provided a glacial refugium for many species, resulting in a unique biota. In the present contribution, a new euscorpiid scorpion with a distinctive morphology, Euscorpius olympus, sp. nov., is described from an isolated population in the foothills of Mount Olympus. This new species raises the number of species in the genus Euscorpius Thorell, 1876, to 74, in Greece to
32, and in the vicinity of Mount Olympus, to three. The roles of climatic oscillations, altitudinal gradients and habitat heterogeneity on the diversity and distributions of the three species occurring around Mount Olympus are briefly discussed.
... The massive species distribution range shifts that took place due to fluctuations of climate conditions since the late Tertiary era (Hewitt, 1996;Comes and Kadereit, 1998;Hewitt, 1999;Hewitt, 2000;Hewitt, 2003;Petit et al., 2003;Hewitt, 2004;Lumibao et al., 2017) offer an appealing framework to assess how plant species migrated as a response to climate change. In Europe, palaeontological and phylogeographic evidence suggest that species either persisted in scattered southern refugia, wherein populations evolved in isolation, generating high genetic differentiation among them (Hewitt, 1999;Hewitt, 2000;Hewitt, 2004;Medail and Diadema, 2009), or in micro-refugia located in the steppe zone South of the ice sheet (Bhagwat and Willis, 2008). ...
Introduction
The dramatic fluctuations of climate conditions since the late Tertiary era have resulted in major species range shifts. These movements were conditioned by geographic barriers and species dispersal capacities. In land plants, gene flow occurs through the movement of male gametes (sperm cells, pollen grains), which carry nDNA, and diaspores (spores, seeds), which carry both cpDNA and nDNA, making them an ideal model to compare the imprints of past climate change on the spatial genetic structures of different genomic compartments. Based on a meta-analysis of cpDNA and nDNA sequence data in western Europe, we test the hypotheses that nDNA genetic structures are similar in bryophytes and spermatophytes due to the similar size of spores and pollen grains, whereas genetic structures derived from the analysis of cpDNA are significantly stronger in spermatophytes than in bryophytes due to the substantially larger size of seeds as compared to spores.
Methods
Sequence data at 1-4 loci were retrieved for 11 bryophyte and 17 spermatophyte species across their entire European range. Genetic structures between and within southern and northern populations were analyzed through F and N statistics and Mantel tests.
Results and discussion
Gst and Nst between southern and northern Europe derived from cpDNA were significantly higher, and the proportion of significant tests was higher in spermatophytes than in bryophytes. This suggests that in the latter, migrations across mountain ranges were sufficient to maintain a homogenous allelic structure across Europe, evidencing the minor role played by mountain ranges in bryophyte migrations. With nDNA, patterns of genetic structure did not significantly differ between bryophytes and spermatophytes, in line with the hypothesis that spores and pollen grains exhibit similar dispersal capacities due to their size similarity. Stronger levels of genetic differentiation between southern and northern Europe, and within southern Europe, in spermatophytes than in bryophytes, caused by higher long-distance dispersal capacities of spores as compared to seeds, may account for the strikingly higher levels of endemism in spermatophytes than in bryophytes in the Mediterranean biodiversity hotspot.
... Other evolutionary processes may, in turn, take place in a recently colonized area. Some of these processes are the founder effect or the bottleneck effect, which cause a reduction or impoverishment of the gene pool of the population 1,8,9 . In turn, the opposite process that may take place in the contact zones between migrating populations may increase genetic diversity 1,6,10,11 . ...
Phylogeographic analysis of Swertia perennis, a typical European subalpine springtime species, revealed the existence of at least five major phylogenetic lineages. A large phylogeographic separation exists among these geographical regions, which confirms the existence of glacial refugia in the Pyrenees, but also in the Eastern and Central Alps. The results obtained from the analyzes indicate the existence of three major differences between the populations of the Alps and the Pyrenees, but also between the populations of the Alps and those of other geographical regions (Carpathians, southern Czech Republic, Sudetes and northern Poland). The studied populations from the Black Forest and from north-eastern and southern Poland are a relic of the former wider distribution of these (periglacial) genetic groups within Swertia perennis. Our results also confirm the existence of biogeographical links between the Carpathians and the Hercynian Range and the Alps. Certainly, there was an exchange of genes between populations located in the eastern Alps, the Carpathians and the Hercynian ranges (Czech Republic, Jeseníky, Sudetes, Ore Mountains). This confirms previous results of comparative studies on the genetic diversity of populations of other vascular plant species.
Premise
Shared geographical patterns of population genetic variation among related species is a powerful means to identify the historical events that drive diversification. The Sphagnum capillifolium complex is a group of closely related peat mosses within the Sphagnum subgenus Acutifolia and contains several circumboreal species whose ranges encompass both glaciated and unglaciated regions across the northern hemisphere. In this paper, we (1) inferred the phylogeny of subg. Acutifolia and (2) investigated patterns of population structure and genetic diversity among five circumboreal species within the S. capillifolium complex.
Methods
We generated RAD sequencing data from most species of the subg. Acutifolia and samples from across the distribution ranges of circumboreal species within the S. capillifolium complex.
Results
We resolved at least 14 phylogenetic clusters within the S. capillifolium complex. Five circumboreal species show some common patterns: One population system comprises plants in eastern North America and Europe, and another comprises plants in the Pacific Northwest or around the Beringian and Arctic regions. Alaska appears to be a hotspot for genetic admixture, genetic diversity, and sometimes endemic subclades.
Conclusions
Our results support the hypothesis that populations of five circumboreal species within the S. capillifolium complex survived in multiple refugia during the last glacial maximum. Long‐distance dispersal out of refugia, population bottlenecks, and possible adaptations to conditions unique to each refugium could have contributed to current geographic patterns. These results indicate the important role of historical events in shaping the complex population structure of plants with broad distribution ranges.
A little more than 10% of the vascular plant flora native to the European Alps is endemic to this area. It has long been noticed that the distribution of endemics across the Alps is very uneven. While most endemics are found along the southern edge of the Alps, with some also on its western, eastern, and northeastern edges, the northern edge of the Alps more or less between Lake Geneva in the west and Lake Traun in the east harbours almost no endemics. The distribution of endemics in the Alps has often been related to the location of glacial refugia. Accordingly, the virtual absence of endemics from the northern edge of the Alps has been explained with the unsuitability of climatic conditions for glacial survival of alpine plants there. After discussing evidence for the existence of glacial refugia for alpine species along the northern edge of the Alps and north of the Alps, I will examine how these refugia differed from refugia along the southern edge of the Alps. I conclude that the uneven distribution of endemics in the Alps is best explained by the different climate through time north and south of the Alps. These climatic differences affected the spatial structure and extent of refugia, the length of isolation of refugial populations, and selective conditions in refugia.
Harpadon nehereus is an ecologically and commercially important fish species. To investigate the phylogeographic pattern and historical demography of H. nehereus, a 1073 base pair fragment of the mitochondrial cytochrome b (Cyt b) gene was analyzed in 305 individuals collected from 13 locations in China offshore. In total, 41 haplotypes and 42 polymorphic sites were detected. Mean haplotype diversity and nucleotide diversity were remarkably low with a range from 0.1630 ± 0.0990 to 0.4113 ± 0.1308 and 0.0002 ± 0.0002 to 0.0007 ± 0.0006, respectively. Insignificant genealogical branches corresponding to sampling locations were revealed both in maximum likelihood (ML) and minimum spanning (MS) trees. The AMOVA and pairwise Fst values indicated shallow genetic structure and the slight genetic variation mainly originated within individuals. Both mismatch distribution analysis and neutrality tests showed H. nehereus had undergone population expansion, which possibly occurred 0.07 million years ago. The bottleneck effect and recent population expansion, combined with larval drift in the ocean current, could be the critical factors in shaping the contemporary phylogeographic patterns and genetic structure of H. nehereus. Our result suggested that H. nehereus in China’s coastal waters may be regarded as an integrated fishery management unit from the perspective of marine resource protection and sustainable utilization. But further researches and comprehensive considerations were still necessary too.
Hybridization and genetic introgression during the speciation process are now believed to be widespread among many animal groups. Extensive hybrid zones and hybrid introgression in Hyalophora are interpreted in relation to these species and speciation concepts. Historical and current evolutionary studies of Hyalophora, and consequent taxonomic revisions, are reviewed. We emphasize those named (e.g., H. “kasloensis”) and unnamed taxa and populations of apparent hybrid origin. A COI phylogenetic analysis of the genus is presented. Hyalophora cecropia shows minimal haplotype divergence over its distribution and does not form hybrid zones in areas of range overlap with congeners. Hyalophora euryalus also shows minimal genetic divergence despite a large West Coast distribution, where it occupies a diversity of plant communities. By contrast, H. columbia gloveri is subdivided into extensive Great Basin and Rocky Mountain haplotype groups. Hyalophora columbia gloveri is distinguished from H. c. columbia by the smallest haplotype divergence of any inter-taxon comparison. We found a shared haplotype between these subspecies from populations located in the northern Rocky Mountains and Minnesota, respectively. The genetic break between eastern and western H. c. columbia populations mirrors a transition zone seen in morphological and ecological characters that is found in eastern Manitoba and western Ontario. Extensive hybridization occurs wherever H. euryalus and H. c. gloveri overlap, varying from narrow hybrid zones to geographically extensive, self-sustaining populations of exclusively hybrid individuals. Several cases of mitochondrial capture were discovered, in which the predominant haplotype of H. euryalus was incorporated at high frequency in both hybrid populations and populations of phenotypically “pure” H. c. gloveri. Newfound larval and adult phenotypic geographic variation is documented and discussed in terms of a possible origin in hybridization and introgression. Select populations are evaluated as possible examples of hybrid species.
Background and aims – Endemism may be defined according to the time of origin of taxa. Neo-endemics refer to relatively recent species that have not dispersed outside their ancestral areas. In contrast, paleo-endemics refer to species of ancient origins, which are currently geographically restricted but probably were more widespread in the past. Geographically, endemism areas may also be based on the co-occurrence of more than one species. We aimed to qualitatively identify the neo-endemism and paleo-endemism of endemic Cactaceae of the Tehuacán-Cuicatlán Valley, as well as to quantitatively assess paleo- and neo-endemics areas.
Material and methods – Using a dated molecular phylogeny of endemic Cactaceae, we defined paleo- and neo-endemics using an arbitrary boundary of 2.6 million years ago; we also assessed the significance of concentrations of these species using a categorical analysis of paleo- and neo-endemism.
Key results – Our results showed that most endemic Cactaceae in the Tehuacán-Cuicatlán Valley arose throughout the Pleistocene, while categorical analysis indicated localised mixed- and super-endemism (including both paleo- and neo-endemics) areas.
Conclusion – We suggest that paleo- and neo-endemics, as well as localised mixed-endemism areas, may have originated due to a probable high climatic stability in the Tehuacán-Cuicatlán Valley, which in addition to topographically rugged and ecologically complex zones (e.g. ecotones, isolated habitat patches) may have allowed it to function as a refuge throughout Pleistocene climatic changes, mainly promoting the speciation of neo-endemics, as well as the persistence of relatively few paleo-endemics.
Arctic char (Salvelinus alpinus) and Dolly Varden (S. malma) are two closely related species in the genus Salvelinus. Both species show substantial intra-specific variation in ecology, morphology, and post-glacial history across their distributional ranges, which has presented substantial challenges for conservation and management and has led to the coining of the term, ‘the charr problem’. Arctic char and Dolly Varden have been studied extensively by scientists since the 1700s, not only because these fishes play important ecological roles within ecosystems, but also because they are culturally, economically, and recreationally valuable. While several detailed reviews have been published on Arctic char over the past 40 years, Dolly Varden remain understudied. In addition, advances in the fields of genetics, ecology, and morphometrics have improved our understanding of the behavior, feeding, habitat requirements, post-glacial histories and intraspecific diversity of each of these two species. Herein, we present an updated review that focuses on placing findings from more recently published (through 2022) phylogenetic, ecological and morphometric studies within the foundational context of earlier papers and reviews (since 1943). We also review anticipated effects of climate change on both species. Across their ranges, Arctic char and Dolly Varden can display a variety of life history types, with many populations exhibiting anadromy and/or potadromy; due to their use of distinct habitats at specific life stages, migratory chars are vulnerable to climate-induced changes to habitat quantity and quality. In addition to reviewing the existing literature, we highlight knowledge gaps and research priorities that, when addressed, will enable more informed conservation and management initiatives for these highly valued fishes.
The Kunming-Montreal Global Biodiversity Framework recognised the urgency of taking action to conserve intraspecific genetic diversity (IGD) as an insurance against habitat degradation and environmental change. Recent work suggests that 90-99% of IGD should be conserved to safeguard viability of future generations.
Here, we addressed such conservation issue in three forest tree species in Italy: silver fir ( Abies alba Mill.), Heldreich’s pine ( Pinus heldreichii H. Christ), and pedunculate oak ( Quercus robur L.). We used microsatellite markers to measure IGD of 36 ( A. alba ), 15 ( P. heldreichii ) and 25 ( Q. robur ) natural sites, including several putative glacial refugia. We developed a Spatial Conservation Prioritisation (SCP) analysis to quantify the genetic irreplaceability of each site and identify the minimum set coverage ensuring IGD protection. Finally, we compared SCP results with the contributions to diversity within and between sites, total allelic richness and private allelic richness.
We found that between 44% and 73% of sites were required to conserve 90-99% of the alleles, and that this conservation effort held even when targeting lower percentages of alleles to protect (50-75%). Glacial refugia were often included in the minimum set coverage, confirming theoretical and biogeographical expectations. Finally, sites with high genetic irreplaceability were found to have higher private allelic richness on average. These results are discussed in the light of the biogeographic history of the species studied and the current policies for the conservation of forest genetic resources.
The alpine plant Bupleurum ranunculoides L. s.l. (Apiaceae) is widely distributed in the European mountains, from the Cantabric range to the Carpathians, passing through the Pyrenees and the Alps. Both the dispersal and the survival of B. ranunculoides are strongly challenged by adequate habitats composed of calcareous substrates, which might have reinforced the tough constrains endured during the pleistocene glaciations. According to the extant literature, this species comprises different cytotypes ranging from diploids to hexaploids that demonstrate a clear pseudo-vicariance : whereas the diploid forms are distributed in the Southern part of the distribution area, the polyploid forms expand throughout the species northern edge. In this study, we aimed to disentangle the biogeographic history of B. ranunculoides by analyzing the spatial genetic structure of this species using an extensive sampling comprising 53 populations distributed throughout its whole range. Using flow cytometry and manual chromosome counting, we were able to provide some supplemental information regarding the distribution of the diploid, tetraploid and hexaploid cytotypes, with hexaploid cytotypes restricted to the populations north to the Alps. Using AFLP, genome fingerprinting and ITS sequencing, we could highlight a relatively deep split between two lineages distributed North vs. South to the Alps. More precisely, five different genetic clusters, two in the Northern and three in the Southern clades were highlighted based on the AFLP data. We suggest that the three genetic clusters from the Southern Alps have survived glaciations in Iberia, Italy, and Balkan refugia, respectively. Regarding the two lineages in the Northern Alps, our data might suggest in situ survival in a peripheral refugium during the last ice age. While both the Northern and Southern lineages have experienced polyploidization processes, only the former encompasses hexaploid lineages. Our study highlights the recent evolutionary history of B. ranunculoides and demonstrates that subspecific treatments are not readily applicable to a taxon with intricate and parallel polyploidization events.
Models of founder events have focused on the reduction in the genetic variation following a founder event. However, recent work (Bryant et al., 1986; Goodnight, 1987) suggests that when there is epistatic genetic variance in a population, the total genetic variance within demes may actually increase following a founder event. Since the additive genetic variance is a statistical property of a population and can change with the level of inbreeding, some of the epistatic genetic variance may be converted to additive genetic variance during a founder event. The model presented here demonstrates that some of the additive-by-additive epistatic genetic variance is converted to additive genetic variance following a founder event. Furthermore, the amount of epistasis converted to additive genetic variance is a function of the recombination rate and the propagule size. For a single founder event of two individuals, as much as 75% of the epistatic variance in the ancestral population may become additive genetic variance following the founder event. For founder events involving two individuals with free recombination, the relative contribution of epistasis to the additive genetic variance following a founder event is equal to its proportion of the total genetic variance prior to the founder event. Traits closely related to fitness are expected to have relatively little additive genetic variance but may have substantial nonadditive genetic variance. Founder events may be important in the evolution of fitness traits, not because they lead to a reduction in the genetic variance, but rather because they lead to an increase in the additive genetic variance.
We surveyed mitochondrial DNA haplotype divergence within and between populations of six species of North American chickadees (Parus, Subgenus Poecile) with the following results. (1) Genotype diversities (range 0.3 to 0.7) and low nucleotide diversities (range 3 to 27 x 10-4) within populations were typical of known vertebrates. (2) The two widespread, northern species (atricapillus and hudsonicus) exhibit little mtDNA genetic differentiation throughout their previously glaciated continental distributions, most likely because of recent, postglacial range expansions. (3) Newfoundland populations of atricapillus and maritime province (Newfoundland plus Nova Scotia) populations of hudsonicus have distinct mtDNA haplotypes which differ from continental haplotypes by single restriction site changes. (4) Haplotypes of the southeastern U.S. species P carolinensis divide into eastern and western sets which have diverged by three percent. This heretofore unrecognized, divided population structure may correspond to the Tombigbee River/Mobile Bay disjunction known in some other vertebrate taxa. (5) Allopatric populations of the southwestern species sclateri and gambeli exhibit divergences of one and three percent respectively. (6) Prevailing interspecific divergence distances of three to seven percent suggest speciation early in the Pleistocene rather than during late (e.g., Wisconsin) glaciations. (7) Phylogenetic analyses suggest that North American taxa include two clades, hudsonicus-rufescens-sclateri versus carolinensis-atricapillus-gambeli and that carolinensis and atricapillus are not sister species.
Species definitions are commonly based on documentation either of genetic or ecologic cohesion (biological species models)
or of phylogenetic relationship (phylogenetic species concept). However, these philosophical positions are often incompatible
with data on genealogical relationship of and genetic/reproductive interactions among member populations. The difficulty in
defining species in nature based on either viewpoint is exacerbated when times between divergence events are short, when differentiation
among populations prior to speciation is extensive, and when reticulation events persist subsequent to speciation. We illustrate
this set of problems with data on mitochondrial DNA sequences and both nuclear sequences and allozyme electromorphs for sets
of populations of two currently recognized species of pocket gophers,Thomomys bottae andT. townsendii in the western United States. These molecular perspectives give somewhat conflicting views of polyphyly, paraphyly, and monophyly
at the population and species level due, in part, to probable differences in times to monophyly, differential lineage sorting,
retention of ancestral polymorphisms, and/or episodes of asymmetrical introgressive hybridization. As a consequence, strict
adherence to any species concept in the objective recognition of evolutionary units within this complex is difficult at best.
Studies of hybrid zones of pocket gophers of the genera Thomomys and Geomys are among the earliest of such endeavors with mammals. It is particularly true for analyses employing relatively sophisticated methodologies to identify individuals of mixed ancestry and to examine the nature of hybridization from genetic and ecological per spectives. Thaeler ‘s (1968a) analysis of three zones of hybridization between taxa of Thomomys in California based on multivariate morphometry illustrated that hybrids could be identified by their morphological intermediacy, and that qualitative differences existed in the extent of hybridization in different contact populations despite similarities in local ecology and zone widths. Patton was the first to use both chromosomal (Patton and Dingman, 1968; Patton, 1973) and allozymic markers (Patton et al., 1972) as genetic tools to define the nature and extent of hybridization in another Thomomys zone in southern Arizona. He and his coworkers showed that F1 hybrids could be differentiated from subsequent filial or backcross individuals, and that the genetic composition of hybrid populations gave direct evidence about hybrid fitness.
Hybrid zones—geographical areas in which the hybrids of two races are found—have attracted the attention of evolutionary biologists for many years, both because they are windows on the evolutionary process and because the patterns of animals and plant variation seen in hybrid zones do not fit traditional classification schemes of taxonomists. Hybrid zones provide insights into the nature of the species, the way barriers to gene exchange function, the genetic basis of those barriers, the dynamics of the speciation process. Hybrid Zones and the Evolutionary Process synthesizes the extensive research literature and points to new directions in research.
The analysis of vegetation history is one of the prime objectives for vegetation scientists. In order to understand the recent composition of local floras and plant communities a second knowledge of species com position during recent millenia is essential. With the present concern over climate changes, due to human activities, an understanding of past vegeta tion distribution becomes even more important, since the correlation between climate and vegetation can often be used to predict possible impacts to crops and forests. I was very fortunate to receive the help of Drs. Webb and Huntley to compile this volume on vegetation history. They have collated an impres sive set of papers which together give an account of the vegetation history of most of the continents during the late-Tertiary and Quaternery periods. There are, however, gaps in the coverage achieved, most notably Africa, and Asia apart from Japan. The information in this book will nonetheless certainly be used widely by vegetation scientists for the regions covered in the book and much of it has relevance to the areas not explicitly described. The authors of the individual chapters have done their best to cover recent topics of interest as well as established facts. It is intended that a separate volume will be produced in the near future covering the vegetation history of Africa and Asia. I thank the editors of It fits well into the this volume for their commendable achievement.
Fundulus heteroclitus is a highly polymorphic fish distributed along the Atlantic coast of North America. Several loci show directional changes in gene frequency with latitude (i.e., clines). Such directional changes have classically been described by two general models: primary and secondary intergradation. Previously, it has not been possible to distinguish between these models for Fundulus heteroclitus on the basis of allelic isozymes or morphological data. However, recent analysis of mitochondrial-DNA (mtDNA) restriction electromorphs helps resolve this issue. Mitochondrial-DNA samples from 48 individuals representing four populations were digested with 17 restriction endonucleases. After electrophoresis, the sizes of the mtDNA fragments were used to analyze the phylogenetic relatedness of fish collected over most of the species range. The analysis clearly identified two major races within the species: a northern and a southern form. The distribution of the mtDNA electromorphs, combined with zoogeographical changes in allelic isozymes and in eggs and adult morphologies (published elsewhere), makes the secondary-intergradation hypothesis most compelling.
Mitochondrial DNA (mtDNA) was used to characterize patterns of geographic variation among white-tailed deer (Odocoileus virginianus) populations in the southeastern United States. Fifteen restriction enzymes were employed to survey and map 99 restriction sites in 142 deer from 18 localities in five southeastern states. Phylogenetic analysis revealed three primary groups of haplotypes: (1) southern Florida and the Florida Keys, (2) the remainder of peninsular Florida northward to South Carolina, and (3) the Florida panhandle westward to Mississippi. Geographical heterogeneity in haplotype frequencies suggests that stochastic lineage sorting or isolation by distance are not important determinates of mtDNA differentiation among deer populations. The pattern of mtDNA variation in white-tailed deer is concordant spatially with those observed in unrelated taxa suggesting the common influence of historical biogeographic events. The data (1) support previous hypotheses that relate contemporary patterns of intraspecific phylogeography in northern Florida to the physiogeographic history of the region; and (2) suggest that genetic differentiation in southern Florida may be attributable to episodes of Pleistocene dispersal. Despite potentially high vagility and human intervention, ecological and demographic characteristics of deer have effectively preserved the historical pattern of intraspecific mtDNA differentiation.
Restriction-fragment polymorphisms in mitochondrial DNA (mtDNA) were used to evaluate population-genetic structure in the desert tortoise Xerobates agassizi and to clarify evolutionary affinities among species of the gopher tortoise complex. Fourteen informative endonucleases were employed to assay mtDNAs from 56 X. agassizi representing 22 locations throughout the species' range. The mtDNA genotypes observed were readily partitioned into three major phylogenetic assemblages, each with striking geographic orientation. Overall, the X. agassizi mtDNA genotypes typify a common phylogeographic pattern, in which broad genetic uniformity of populations is interrupted by geographic features that presumably have functioned as dispersal barriers. The geologic history of the Colorado River area, which includes extensive marine incursions, may account for the marked mtDNA divergence between eastern and western X. agassizi assemblages. In mtDNA comparisons among the four species of the gopher tortoise complex, both UPGMA and Wagner parsimony analysis strongly support the recognition of two distinct species groups previously suggested by traditional systematic approaches. Furthermore, the mtDNA data identify the eastern X. agassizi assemblage as the probable inceptive lineage of X. berlandieri. Results from both intra- and interspecific comparisons illustrate how clues to historical events may be present in the geographic structure of mtDNA phylogenies.
Restriction-endonuclease-site variation of mitochondrial DNA (mtDNA) was used to investigate patterns of geographic and phylogenetic divergence within the rodent genus Onychomys. Onychomys has occupied arid habitats in the western North American deserts, shrub-steppes, and grasslands since the late Tertiary. A phylogenetic analysis of the total mtDNA restriction-site variation throughout the range of Onychomys suggests that the distribution of this genus has been affected by the same Quaternary pluvial-interpluvial climatic fluctuations that have resulted in the periodic fragmentation of arid habitats in western North America. Onychomys mtDNA haplotypes define at least five discrete geographical subsets, suggesting that there are five areas of endemism for biota restricted to arid and semiarid habitats in North America. The mtDNA-haplotype phylogeny can be used to infer an hypothesis of historical relationships among the five areas of endemism as follows: ([{(Wyoming Basin + Interior Plains + Colorado Plateaus) + (Columbia Basin + Great Basin)} + Gulf Coastal Plain] + Chihuahuan) + Western Deserts. The results of this study point to the potential use of mtDNA-haplotype phylogenies to reconstruct historical biogeographic events in Quaternary time. The utility of mtDNA variation depends in part on the ecology and distribution of the species being examined. Therefore, our hypothesized area cladogram can be tested by investigating regional relationships in other western North American taxa with distributions similar to Onychomys.
Mitochondrial DNA (mtDNA) haplotypes were determined for 118 individuals of 13-and 17-year periodical cicadas (genus Magicicada) collected from 16 localities throughout the Midwest and eastern United States. Two distinct mtDNA lineages, identified as A and B, differ by 2.5% based on analysis of fragment patterns and restriction maps. Observed levels of mtDNA diversity within each lineage are low compared to estimates for other taxa. The two lineages are regionally segregated, with the boundary line occurring at a latitude of approximately 33° North. The levels of mtDNA diversity and population genetic structure differ within the two lineages. There is a remarkably low level of mean mtDNA divergence and no genetic structure in lineage A, whereas lineage B exhibits an order of magnitude higher level of mtDNA diversity and significant genetic structure among sampled populations. The low level of mtDNA diversity in cicadas may be attributed to (1) a population bottleneck that most likely occurred during the Pleistocene, (2) recent colonization following the retreat of the glaciers and the expansion of deciduous forests, and/or (3) high among-family reproductive variance (as a consequence of large population size, high fecundity, aggregative behavior of adults, and clumping of eggs). The difference in mtDNA diversity and population genetic structure between the lineages suggests that they experienced different biogeographic histories; we relate this to Pleistocene changes.
Gene flow can effectively suppress genetic divergence among widely separated populations in highly mobile species. However, the same may not be true of species that typically disperse over shorter distances. Using mtDNA restriction-site and sequence analyses, we evaluate the extent of divergence among populations of two small relatively sedentary North American canids, the kit and swift foxes (genus Vulpes). We determine the significance of genetic differentiation among populations separated by distance and those separated by discrete topographic barriers. Our results show the among-population component of genetic variation in kit and swift foxes is large and similar to that of small rodents with limited dispersal ability. In addition, we found two distinct groupings of genotypes, separated by the Rocky Mountains, corresponding to the traditional division between kit and swift fox populations. Previous workers have characterized these morphologically similar populations either as separate species or subspecies. Our mtDNA data also suggest that kit and swift fox populations hybridize over a limited geographic area. However, the sequence divergence between kit and swift foxes is similar to that between these taxa and the arctic fox (Alopex lagopus), a morphologically distinct species commonly placed in a separate genus. This result presents a dilemma for species concepts, and we conclude that kit and swift foxes should be recognized as separate species.
Preface. Part I: Background: 1. Introduction. Why Employ Molecular Genetic Markers? Why Not Employ Molecular Genetic Markers? 2. History of Molecular Phylogenetics. Debates and Diversions from Molecular Systematics. Molecular Phylogenetics. 3. Molecular Tools. Protein Assays. DNA Assays. References to Laboratory Protocols. 4. Interpretative Tools. Categorical Subdivisions of Molecular Genetic Data. Molecular Clocks. Procedures for Phylogeny Reconstruction. Gene Trees versus Species Trees. Part II: Applications: 5. Individuality and Parentage. Genetic Identity versus Non-Identity. Parentage. 6. Kinship and Intraspecific Phylogeny. Close Kinship and Family Structure. Geographic Population Structure and Gene Flow. Phylogeography. Microtemporal Phylogeny. 7. Speciation and Hybridization. The Speciation Process. Hybridization and Introgression. 8. Species Phylogenies and Macroevolution. Rationales for Phylogeny Estimation. Special Approaches to Phylogeny Estimation. Prospectus for a Global Phylogeny. Special Topics in Molecular Phylogenetics. 9. Conservation Genetics. Issues of Heterozygosity. Issues of Phylogeny. Literature Cited. Index to Taxonomic Genera. General Index.
The nucleotide sequences of segments of the cytochrome b gene (351 bp), the tRNA(Pro) gene (49 bp), and the control region (approximately 313 bp) of mitochondrial DNA were obtained from 26 fish representing different populations and species of Melanotaenia and one species of Glossolepis, freshwater rainbow fishes confined to Australia and New Guinea. The purpose was to investigate relative rates and patterns of sequence evolution. Overall levels of divergence were similar for the cytochrome b and tRNA control-region sequences, both ranging from < 1% within subspecies to 15%-19% between genera. However, the patterns of sequence evolution differed. For the cytochrome b gene, transitions consistently exceeded transversions, the bias ranging from 4.2:1 to 2:1, depending on the level of sequence divergence. However, in the control-region sequence, a bias toward transitions (2:1) was observed only in comparisons between very similar sequences, and transversions outnumbered transitions in comparisons of divergent sequences. Graphic comparisons suggested that the control region was saturated for transitions at relatively low levels of sequence divergence but accumulated transversions at a greater rate than did the cytochrome b sequence. These distinct patterns of base substitution are associated with differences in A+T content, which is 70% for the tRNA control-region segment versus 50% for cytochrome b. A test for skewness in the distribution of lengths of random trees indicated that both segments contained phylogenetic signal. Parsimony analyses of the data from the two regions, with or without weighting schemes appropriate to the respective patterns of sequence evolution, identified the same five groupings of sequences, but the relationships among the groups differed. However, in most cases the branches uniting different combinations of groups were poorly supported, and the differences among topologies were insignificant. Considering the observed patterns of base substitution and the results of the phylogenetic analyses, we deduce that both the control region and cytochrome b are appropriate for population genetic studies but that the control region is less effective than cytochrome b for resolving relationships among divergent lineages of rainbow fishes.
Restriction fragment length polymorphisms in mitochondrial DNA (mtDNA) were used to reconstruct evolutionary relationships of conspecific populations in four species of freshwater fish—Amia calva, Lepomis punctatus, L. gulosus, and L. microlophus. A suite of 14-17 endonucleases was employed to assay mtDNAs from 305 specimens collected from 14 river drainages extending from South Carolina to Louisiana. Extensive mtDNA polymorphism was observed within each assayed species. In both phenograms and Wagner parsimony networks, mtDNA clones that were closely related genetically were usually geographically contiguous. Within each species, major mtDNA phylogenetic breaks also distinguished populations from separate geographic regions, demonstrating that dispersal and gene flow have not been sufficient to override geographic influences on population subdivision.—Importantly, there were strong patterns of congruence across species in the geographic placements of the mtDNA phylogenetic breaks. Three major boundary regions were characterized by concentrations of phylogenetic discontinuities, and these zones agree well with previously described zoogeographic boundaries identified by a different kind of data base—distributional limits of species—suggesting that a common set of historical factors may account for both phenomena. Repeated episodes of eustatic sea level change along a relatively static continental morphology are the likely causes of several patterns of drainage isolation and coalescence, and these are discussed in relation to the genetic data.—Overall, results exemplify the positive role that intraspecific genetic analyses may play in historical zoogeographic reconstruction. They also point out the potential inadequacies of any interpretations of population genetic structure that fail to consider the influences of history in shaping that structure.
Hybrid zones are regions of steep genotypic transition between populations that have reached a level of divergence comparable to that between “good” species. Remarkably, however, hybrid zones appear to be equilibrium configurations where the parental populations (whether they are called species, subspecies, or races) retain their taxonomic identity and integrity even though reproductive isolation is incomplete or, in many instances, wholly lacking. Although species definitions remain very much in contention (Mayr, 1957, 1987; Ehrlich, 1961; Sokal and Crovello, 1970; Mishler and Donoghue, 1982; Cracraft, 1983; Ghiselin, 1987; McKitrick and Zink, 1988; Endler, 1989; Templeton, 1989; Moor , 1990), we think there would be unanimity that an essential property of a species is that there is uniformity of genotype within the species and a discontinuity between the genotype of one species and that of another. In other words, genotypic variance within a species is low compared to the variance between species. Reproductive isolation, of course, would enforce this essential property of species, but the sustained cohesion (sensu Templeton, 1989) of the hybridizing taxa and the abrupt discontinuity of genotype seen across hybrid zones imply that forces more fundamental than reproductive isolation are involved in speciation. Hybrid zones pro vide natural experimental systems where modern genetic analysis can be applied to discern the forces that drive the origin of species.
Effects of a population bottleneck (founder-flush cycle) upon quantitative genetic variation of morphometric traits were examined in replicated experimental lines of the housefly founded with one, four or 16 pairs of flies. Heritability and additive genetic variances for eight morphometric traits generally increased as a result of the bottleneck, but the pattern of increase among bottleneck sizes differed among traits. Principal axes of the additive genetic correlation matrix for the control line yielded two suites of traits, one associated with general body size and another set largely independent of body size. In the former set containing five of the traits, additive genetic variance was greatest in the bottleneck size of four pairs, whereas in the latter set of two traits the largest additive genetic variance occurred in the smallest bottleneck size of one pair. One trait exhibited changes in additive genetic variance intermediate between these two major responses. These results were inconsistent with models of additive effects of alleles within loci or of additive effects among loci. An observed decline in viability measures and body size in the bottleneck lines also indicated that there was nonadditivity of allelic effects for these traits. Several possible nonadditive models were explored that increased additive genetic variance as a result of a bottleneck. These included a model with complete dominance, a model with overdominance and a model incorporating multiplicative epistasis.
Asks: 1) What is the effect of the invasion process on the amount of genetic variation in populations? 2) What levels of genetic variation are found in species that are successful invaders? 3) What genetic systems are associated with colonising success? 4) What are the relative contributions of inherited and environmentally controlled variation in life history traits of colonising species? 5) What evidence exists for local genetic differentiation following invasions? Examples are drawn from plant and animal invasions of Australia.-from Authors
Mitochondrial DNA was purified from four species of higher primates (Guinea baboon, rhesus macaque, guenon, and human) and digested with 11 restriction endonucleases. A cleavage map was constructed for the mitochondrial DNA of each species. Comparison of the maps, aligned with respect to the origin and direction of DNA replication, revealed that the species differ from one another at most of the cleavage sites. The degree of divergence in nucleotide sequence at these sites was calculated from the fraction of cleavage sites shared by each pair of species. By plotting the degree of divergence in mitochondrial DNA against time of divergence, the rate of base substitution could be calculated from the initial slope of the curve. The value obtained, 0.02 substitutions per base pair per million years, was compared with the value for single-copy nuclear DNA. The rate of evolution of the mitochondrial genome appears to exceed that of the single-copy fraction of the nuclear genome by a factor of about 10. This high rate may be due, in part, to an elevated rate of mutation in mitochondrial DNA. Because of the high rate of evolution, mitochondrial DNA is likely to be an extremely useful molecule to employ for high-resolution analysis of the evolutionary process.
Ostrinia nubilalis (Hubner) is an introduced insect species belonging to the order Lepidoptera that has had a significant impact on the production of Zea mays L., field maize, and particularly sweet maize, as well as other host plants that possess stems (North Cent. Reg. Comm. NC-105, 1972). Therefore, studies of geographic variation in this introduced species may be of great practical as well as basic significance.
It can be demonstrated that many species which have today a Mediterranean range, extended their northern limits during the warmer interglacial and interstadial interludes, at least as far as the British Isles. These species comprised groups of varied ecological preferences and some have such restricted present day distributions that they have been viewed as "endemic' Mediterranean species. Patterns of present day geographical distributions are thus the result of dynamic interaction between the species and the numerous and intense climatic changes that caused continuous biogeographic adjustments. -from Author
From a study of the geographic occurrences of contemporary hybridization among North American animals, it has become apparent that most of the hybrids are produced in a few relatively localized zones, with little hybridizing in the vast areas between these zones of mixing. The hybrids tend to be at least moderately fertile and therefore to be a source of significant gene exchange between the typically allopatric pairs of species and semispecies. There is a wide variety of consequences from this introgression, with greater or lesser influence on the parental populations, and large portions of the fauna and probably flora are involved. An appropriate term for such a belt of interfaunal and interfloral linkage is suture-zone.1
We present an extensive analysis of mitochondrial DNA (mtDNA) nucleotide sequence variation within the rodent Peromyscus maniculatus Using techniques which allow assay of mtDNA from individual animals, we have mapped variable and conserved cleavage sites for eight restriction endonucleases in mtDNA prepared from 135 animals collected throughout North America. The data provide information on two different but interrelated aspects of mtDNA evolution: (1) the nature of evolutionary change in the molecule itself; and (2) the implications of these molecular changes for estimating matriarchal relationships within P maniculatus. Our data support the hypothesis that mammalian mtDNA evolves primarily by the accumulation of single base substitutions which occur in most of the coding regions of the genome. Sequence divergence between P. maniculatus mtDNA samples can be as high as seven percent. The distributions of cleavage sites and the magnitudes of sequence divergence among samples, are strongly related to the geographic sources of collections. The data clearly distinguish five major genetic assemblages within P maniculatus, as well as extensive clonal diversity within each of those assemblages. Convergent or parallel sequence alterations are not uncommon. Phylogenies derived from mtDNA restriction analysis are not generally concordant with those previously estimated from morphological consideration.
We begin a characterization of the evolutionary dynamics of mitochondrial DNA (mtDNA) in fishes by examining restriction site variability in 189 bluegill sunfish (Lepomis macrochirus). A total of 15 endonucleases was employed to map 37 restriction sites in mtDNA from selected individuals. Genome size was approximately 16.2 kilobases. All differences between genotypes could be accounted for by gains or losses of individual sites, without additions, deletions, or rearrangements affecting more than about 50-250 base-pairs. Two highly distinct mtDNA genomes, differing by 20 assayed mutation steps and an estimated 8.5% sequence divergence, were discovered. Both genomes were observed in high frequency in a sample of 151 bluegill from a north-Georgia population, which on the basis of allozyme genotype appears to represent a freely-interbreeding hybrid swarm between two bluegill subspecies. Within the hybrid population, mtDNA and allozyme genotypes were associated approximately at random. The distinct genetic markers provided by the mtDNA genomes provided an improved test of the possibility of within-individual mtDNA polymorphism because true heteroplasmicity could readily be distinguished from results of incomplete digests. Nonetheless, in somatic or germ cells, no individual bluegill exhibited mtDNA heteroplasmicity (at 5% or greater level) that could be explained by paternal mtDNA transmission. Additional samples from Louisiana to Florida tentatively confirm that the geographic distributions of the two distinct mtDNA genomes are highly concordant with the previously described ranges of L. m. macrochirus and L. m. purpurescens defined by morphology and allozymes. Overall, the results on mtDNA variability in bluegill conform to and strengthen some of the more straightforward expectations about the pattern of evolution of uniparentally-transmitted genomes in sexually reproducing populations.
Genetic variation was assessed in the tiger beetle, Cicindela dorsalis, by sequencing of three regions of the mtDNA genome. Populations of four morphologically distinguishable subspecies were sampled from 28 representative locations covering almost the entire geographic range of the species in coastal North America. In 78 individuals analyzed for 656 base pairs from four different genes, 17 different haplotypes could be distinguished. A cladistic analysis grouped the haplotype sequences into two main lineages, one from the Atlantic Ocean and one from the Gulf of Mexico. Haplotypes within the two clades were very similar to each other. Most of the characters that distinguished these closely related haplotypes were homoplastic. The geographic distribution of haplotypes did not coincide with the distribution of morphological subspecies, but no evidence for hybridization between two subspecies could be inferred from this observation. The implications of these findings for the evolution of gene sequences at and below the species level are discussed.
Gene flow can effectively suppress genetic divergence among widely separated populations in highly mobile species. However, the same may not be true of species that typically disperse over shorter distances. Using mtDNA restriction-site and sequence analyses, we evaluate the extent of divergence among populations of two small relatively sedentary North American canids, the kit and swift foxes (genus Vulpes). We determine the significance of genetic differentiation among populations separated by distance and those separated by discrete topographic barriers. Our results show the among-population component of genetic variation in kit and swift foxes is large and similar to that of small rodents with limited dispersal ability. In addition, we found two distinct groupings of genotypes, separated by the Rocky Mountains, corresponding to the traditional division between kit and swift fox populations. Previous workers have characterized these morphologically similar populations either as separate species or subspecies. Our mtDNA data also suggest that kit and swift fox populations hybridize over a limited geographic area. However, the sequence divergence between kit and swift foxes is similar to that between these taxa and the arctic fox (Alopex lagopus), a morphologically distinct species commonly placed in a separate genus. This result presents a dilemma for species concepts, and we conclude that kit and swift foxes should be recognized as separate species.
The extent of genome-wide restructuring predicted in bottleneck models of speciation is addressed in assays of non-reproductive behavior in lines of the housefly. After five serial founderflush cycles of one of three sizes (1, 4, or 16 pairs), each bottleneck line showed significant differentiation from the outbred control in ambulatory levels and grooming sequences in videotaped records of precopulatory activity. Only one line (4-pair) showed overall lethargy which was associated to inbreeding depression in egg-to-adult viability, thus exemplifying a case of probable extinction due to bottlenecks. The two most hyperactive lines (1- and 16-pair) showed very similar directions of differentiation from the control in locomotor activity and grooming behavior, as well as in mating behavior evaluated from a separate study. This high congruence suggested that directional selection toward the phenotypic optima of the ancestor operated on the bottleneck populations and that a 10-fold difference in theoretical inbreeding coefficients did not affect the magnitude of response. The remaining two bottleneck lines showed some independence from these general trajectories, their divergence along minor axes of ancestral intercorrelation structure possibly being more important to the formation of new species. Significant perturbations of the thresholds for execution of grooming and locomotor movements suggested increased evolutionary potential for ritualization (i.e., sexual selection for adoption of non-reproductive behavior into courtship repertoire) due to bottlenecks.
Mitochondrial DNA (mtDNA) haplotypes were determined for 118 individuals of 13-and 17-year periodical cicadas (genus Magicicada) collected from 16 localities throughout the Midwest and eastern United States. Two distinct mtDNA lineages, identified as A and B, differ by 2.5% based on analysis of fragment patterns and restriction maps. Observed levels of mtDNA diversity within each lineage are low compared to estimates for other taxa. The two lineages are regionally segregated, with the boundary line occurring at a latitude of approximately 33⚬ North. The levels of mtDNA diversity and population genetic structure differ within the two lineages. There is a remarkably low level of mean mtDNA divergence and no genetic structure in lineage A, whereas lineage B exhibits an order of magnitude higher level of mtDNA diversity and significant genetic structure among sampled populations. The low level of mtDNA diversity in cicadas may be attributed to (1) a population bottleneck that most likely occurred during the Pleistocene, (2) recent colonization following the retreat of the glaciers and the expansion of deciduous forests, and/or (3) high among-family reproductive variance (as a consequence of large population size, high fecundity, aggregative behavior of adults, and clumping of eggs). The difference in mtDNA diversity and population genetic structure between the lineages suggests that they experienced different biogeographic histories; we relate this to Pleistocene changes.
Fundulus heteroclitus is a highly polymorphic fish distributed along the Atlantic coast of North America. Several loci show directional changes in gene frequency with latitude (i.e., clines). Such directional changes have classically been described by two general models: primary and secondary intergradation. Previously, it has not been possible to distinguish between these models for Fundulus heteroclitus on the basis of allelic isozymes or morphological data. However, recent analysis of mitochondrial-DNA (mtDNA) restriction electromorphs helps resolve this issue. Mitochondrial-DNA samples from 48 individuals representing four populations were digested with 17 restriction endonucleases. After electrophoresis, the sizes of the mtDNA fragments were used to analyze the phylogenetic relatedness of fish collected over most of the species range. The analysis clearly identified two major races within the species: a northern and a southern form. The distribution of the mtDNA electromorphs, combined with zoogeographical changes in allelic isozymes and in eggs and adult morphologies (published elsewhere), makes the secondary-intergradation hypothesis most compelling.
Guppies were sampled from eight populations representing four river drainage basins in northern Trinidad, and from one population on the nearby island of Tobago. For each individual, a 465 base pair (bp) segment of the control region of the mitochondrial genome was sequenced. The resulting DNA sequences were subjected to sequence divergence calculations and the populations were linked by maximum parsimony analysis to determine their phylogenetic relationships. Mitochondrial DNA (mtDNA) sequence variation was found both within and between river drainages, correlated with the geographic features of northern Trinidad. The variation observed exists primarily between drainages, particularly between the Oropuche drainage and all other Trinidad drainages examined. Estimates of time of divergence between guppy populations of different drainages, based on mtDNA sequence variation, ranged from 100,000 to 200,000 for the most recently separated populations and from 600,000 to 1.2 million years between the Oropuche populations and all others examined. Examination of fish from northeastern South America will be required to determine whether these populations differentiated in their present locations or were the result of separate invasions of Trinidad from different Venezuelan sources. However, genetic isolation of these populations appears to predate the current physical separation of the island of Trinidad from the Venezuelan mainland.
Restriction-fragment polymorphisms in mitochondrial DNA (mtDNA) were used to evaluate population-genetic structure in the desert tortoise Xerobates agassizi and to clarify evolutionary affinities among species of the gopher tortoise complex. Fourteen informative endonucleases were employed to assay mtDNAs from 56 X. agassizi representing 22 locations throughout the species' range. The mtDNA genotypes observed were readily partitioned into three major phylogenetic assemblages, each with striking geographic orientation. Overall, the X. agassizi mtDNA genotypes typify a common phylogeographic pattern, in which broad genetic uniformity of populations is interrupted by geographic features that presumably have functioned as dispersal barriers. The geologic history of the Colorado River area, which includes extensive marine incursions, may account for the marked mtDNA divergence between eastern and western X. agassizi assemblages. In mtDNA comparisons among the four species of the gopher tortoise complex, both UPGMA and Wagner parsimony analysis strongly support the recognition of two distinct species groups previously suggested by traditional systematic approaches. Furthermore, the mtDNA data identify the eastern X. agassizi assemblage as the probable inceptive lineage of X. berlandieri. Results from both intra- and interspecific comparisons illustrate how clues to historical events may be present in the geographic structure of mtDNA phylogenies.
Geographic variation at 24 polypeptide loci was studied in 24 populations of the red-backed salamander, Plethodon cinereus. At 6 loci, differentiation of the continuously distributed northern populations from the five southern isolates is complete or almost complete. The latter are recognized as a separate species, P. serratus. Differentiation within P. serratus is modest. The seven samples of P. cinereus that were collected from formerly glaciated areas are very uniform, while there is substantial divergence among the eight samples from unglaciated localities. Colonization since the last Pleistocene glaciation has apparently represented only a small portion of the diversity of the potential source area.
Recognition of the distinction between population expansion and arrival of a species is crucial for interpreting pollen diagrams. F. grandifolia probably occurred during the Wisconsin full-glacial (18 000 BP) as a scarce tree over much of SE North America, and did not have a localized 'refugium'. By 14 000 BP it had begun spreading north, still at very low population densities. Between 14 000 and 10 000 BP it reached high densities locally in the southeast, probably as the result of population expansion while the climate was temporarily favourable. F. grandifolia had reached approximately to its present geographic limits by 7000 BP, but continued to spread, at a lower rate, in some areas until the present. The E Great Lakes region, where F. grandiflora is most abundant today, had the most rapid population expansions, at c7000 BP, attributed to locally favourable environmental conditions. The spread of F. grandifolia across the continent was achieved at very low population densities. The detection and tracking of such a spread is only marginally possible with current pollen-analytical techniques. -from Author
Coleoptera are abundant fossils in Quaternary deposits laid down under
freshwater or terrestrial conditions. They display a remarkable degree
of evolutionary stability and reasons are adduced for believing that
this morphological constancy is associated with physiological constancy.
Thus whole communities of species have been assembled in the past, drawn
together by common ecological preferences, so that the species
composition of fossil assemblages resembles that of modern faunas.
Marked changes in the geographical distribution of Coleoptera during the
last glacial-interglacial cycle conform to an orderly pattern of
climatic fluctuations. The Coleoptera contribute most information about
the Devensian climates during warmer interstadial periods because during
the colder episodes conditions in Britain became more or less
intolerable to insect life and the fossil content of the sediments
approaches zero. The term interstadial is here used for an interlude of
milder climate in an otherwise cold period which either does not attain
temperatures equivalent to those of the present day or which attains
temperatures as warm, or even warmer than those of today but which does
not last long enough for floral and faunal equilibrium to become
established. During the Chelford Interstadial, at the limit of
acceptable radiocarbon dating but possibly about 60 000 years (a) ago,
the climate in central Britain was rather cooler than now with a
moderate degree of continentality. The Upton Warren Interstadial
complex, between about 45 000 and 25 000 a ago, reached its thermal
maximum at about 43 000 a before present when temperatures were rather
higher than those of the present day and the climate was moderately
oceanic. This episode may have been as short in duration as 1000 a.
After this the interstadial is characterized by a period of much lower
temperatures, with a greatly increased degree of climatic
continentality, lasting for about 15 000 a. Few insect faunas are known
from the period of maximum ice expansion but the scant evidence supports
an interpretation of a climate of arctic severity. During the closing
phases of the Devensian cold period there is faunal evidence for only
one major climatic oscillation - here called the Windermere
Interstadial. The sharp rise in the thermal environment at its beginning
took place rather before 13 000 a ago but later than 14 000 a ago.
Thermal maximum was attained almost immediately with temperatures during
the summer at or above their present day level. Moderate oceanicity of
the climate at this time means that winter temperatures were not much
lower than those of the present day. At least during the earliest parts
of this interstadial a temperate insect fauna was associated with a
flora almost entirely dominated by herbs. The decline of the Windermere
Interstadial from its thermal maximum seems to have been more or less
synchronous from southern to northern England and to have taken place at
about 12 200 a ago. A cool temperate phase then ensued for over one
thousand years with summers about 3 ^circC cooler than during the
thermal maximum. This episode corresponds in time to the Allerod
oscillation. The Loch Lomond Stadial between 11 000 and 10 000 a ago saw
the return of arctic faunas to the British Isles even as far south as
Cornwall. The presence of Asiatic species, though not abundant, suggests
that the climate at this time may have been rather continental. The
timing and intensity of the climatic changes during deglaciation show
close parallelism to the changes in oceanic circulation in the eastern
Atlantic now being interpreted from cores of ocean bottom sediments.
Two subspecies of the grasshopper Chorthippus parallelus meet and form a hybrid zone in the Pyrenees. Both strong hybrid dysfunction and a behavioural difference occur, which would seem to make the zone a suitable candidate for speciation by reinforcement. One of the classic ways of looking for this is to test for increased levels of assortative mating between populations from close to the region of contact. Here we show that, with virgin insects, such assortment decreases as one approaches the centre of the zone in C. parallelus. The pattern is different upon remating, with non-virgins showing a pattern more like that predicted by reinforcement. Overall there is little evidence for reinforcement. We argue that other tests of the model may be more appropriate for stable hybrid zones.