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Do island populations have less genetic variation than mainland populations?
Abstract
Island populations are much more prone to extinction than mainland populations. The reasons for this remain controversial. If inbreeding and loss of genetic variation are involved, then genetic variation must be lower on average in island than mainland populations. Published data on levels of genetic variation for allozymes, nuclear DNA markers, mitochondrial DNA, inversions and quantitative characters in island and mainland populations were analysed. A large and highly significant majority of island populations have less allozyme genetic variation than their mainland counterparts (165 of 202 comparisons), the average reduction being 29 per cent. The magnitude of differences was related to dispersal ability. There were related differences for all the other measures. Island endemic species showed lower genetic variation than related mainland species in 34 of 38 cases. The proportionate reduction in genetic variation was significantly greater in island endemic than in nonendemic island populations in mammals and birds, but not in insects. Genetic factors cannot be discounted as a cause of higher extinction rates of island than mainland populations.
... Several factors contribute to this variation. First, limited dispersal and isolation have a notable impact on An. baimaii populations across different islands, leading to genetic differentiation (Frankham 1997). Second, the founder effect and genetic drift are particularly influential in island populations. ...
... A small number of individuals colonizing a new area can lead to a population with initially limited genetic variation. Over time, genetic drift, characterized by random changes in allele frequencies, can introduce significant variability within these populations (Barton 1996;Frankham 1997). ...
... However, the existence of unique haplotypes at each site also points to genetic differentiation, likely a result of the islands' geographic isolation. Such isolation restricts gene flow and contributes to the distinctive genetic characteristics observed in these island populations (Frankham 1997). ...
Anopheles baimaii (Diptera: Culicidae) significantly contributes to the transmission of parasites causing malaria in Southeast Asia and South Asia. This study examined the morphological (wing shape) and molecular (mitochondrial gene) variations of An. baimaii in four of Thailand’s border islands, and also investigated the presence of Plasmodium parasites in these mosquitoes. No Plasmodium infections were detected in the samples. Significant differences in wing shape were observed in most island populations (p < 0.05). A single-linkage tree, constructed using Mahalanobis distances, clustered the populations into two groups based on geographical locations. Genetic variation in An. baimaii was also analyzed through cytochrome c oxidase subunit I (COI) gene sequences. This analysis identified 22 segregating sites and a low nucleotide diversity of 0.004. Furthermore, 18 distinct haplotypes were identified, indicating a high haplotype diversity of 0.825. Neutrality tests for the overall population revealed a significantly negative Fu’s Fs value (-5.029), indicating a population expansion. In contrast, Tajima’s D yielded a negative value (-1.028) that did not reach statistical significance. The mismatch distribution analysis exhibited a bimodal pattern, and the raggedness index was 0.068, showing no significant discrepancy (p = 0.485) between observed and expected distributions. Pairwise genetic differentiation assessments demonstrated significant differences between all populations (p < 0.05). These findings provide valuable insights into the COI gene and wing morphometric variations in An. baimaii across Thailand's islands, offering critical information for understanding the adaptations of this malaria vector and guiding future comprehensive research.
... The geographic isolation through barriers results in distinct genetic signatures that are exacerbated in island populations (Frankham 1998). The low standing genetic variation of few founding individuals and limited dispersal between small fragmented patches of habitat that provide limited resources result in low genetic diversity and small population sizes (Frankham 1996(Frankham , 1997Brüniche-Olsen et al. 2019). ...
... Genomic signatures of isolation in Galapagos bullhead sharks are consistent with the gradual formation of barriers to dispersal and resemble those typical of terrestrial island biogeography. In oceanic islands, species with low dispersal commonly have lower genetic diversity and smaller population sizes compared to mainland populations owing to the reduced genetic variation of few founding individuals and because limited resources in small and fragmented habitats sustain smaller populations (Frankham 1996(Frankham , 1997. Galapagos bullhead sharks show lower diversity, based on similar sequencing techniques and numbers of markers, compared to shark species with higher dispersal or that were sampled along continental ranges (Supplementary Information Table S5). ...
... Galapagos bullhead sharks have low dispersal capacity and smaller populations sizes, in comparison. Therefore, low genomic diversity may be traced back to a founder effect caused by few colonizing individuals, a common feature in terrestrial island populations (Frankham 1997). Considering its poor dispersal ability, Galapagos bullhead sharks or their egg cases attached to debris could have been transported from the South American coast to the Galapagos on rafts drifting with the Humboldt Current, similar to the mechanism proposed for many native terrestrial vertebrates (Ali and Fritz 2021). ...
Oceanic islands play a central role in the study of evolution and island biogeography. The Galapagos Islands are one of the most studied oceanic archipelagos but research has almost exclusively focused on terrestrial organisms compared to marine species. Here we used the Galapagos bullhead shark ( Heterodontus quoyi ) and single nucleotide polymorphisms (SNPs) to examine evolutionary processes and their consequences for genetic divergence and island biogeography in a shallow-water marine species without larval dispersal. The sequential separation of individual islands from a central island cluster gradually established different ocean depths between islands that pose barriers to dispersal in H. quoyi . Isolation by resistance analysis suggested that ocean bathymetry and historical sea level fluctuations modified genetic connectivity. These processes resulted in at least three genetic clusters that exhibit low genetic diversity and effective population sizes that scale with island size and the level of geographic isolation. Our results exemplify that island formation and climatic cycles shape genetic divergence and biogeography of coastal marine organisms with limited dispersal comparable to terrestrial taxa. Because similar scenarios exist in oceanic islands around the globe our research provides a new perspective on marine evolution and biogeography with implications for the conservation of island biodiversity.
... Our findings are consistent with previous studies on other species, which have shown that populations with limited gene flow are more prone to inbreeding and the accumulation of deleterious alleles (Frankham, 2015;Frankham, 1997;Keller and Waller, 2002;Lynch et al., 1995). Islands have also previously been shown to harbour less diverse populations of northern quolls (von Takach et al., 2022b), a common feature of island populations that results from the combined effects of isolation, genetic drift, and founder effects (Frankham, 1997). ...
... Our findings are consistent with previous studies on other species, which have shown that populations with limited gene flow are more prone to inbreeding and the accumulation of deleterious alleles (Frankham, 2015;Frankham, 1997;Keller and Waller, 2002;Lynch et al., 1995). Islands have also previously been shown to harbour less diverse populations of northern quolls (von Takach et al., 2022b), a common feature of island populations that results from the combined effects of isolation, genetic drift, and founder effects (Frankham, 1997). Genomic assessments for various Australian species, including the golden bandicoot (Isoodon auratus) and the boodie (Bettongia lesueur) (Nistelberger et al., 2023), have consistently found substantially higher genomic diversity in mainland Australian populations compared to island refuges, and it appears that only very large islands naturally support populations with comparable levels of genomic diversity to mainland areas von Takach et al., 2021). ...
In our present age of extinction, conservation managers must use limited resources efficiently to conserve species and the genetic diversity within them. To conserve intraspecific variation, we must understand the geographic distribution of the variation and plan management actions that will cost-effectively maximise its retention. Here, we use a genome-wide single-nucleotide polymorphism (SNP) dataset consisting of 12,962 loci and 384 individuals to inform conservation management of the Endangered northern quoll (Dasyurus hallucatus), a carnivorous marsupial distributed patchily across northern Australia. Many northern quoll populations have declined or are currently declining, driven by the range-expanding cane toad (Rhinella marina). We (1) confirm population genomic structure, (2) investigate the contribution of each population to overall diversity, (3) conduct genomic prioritisation analyses at several spatial and hierarchical scales using popular conservation planning algorithms, and (4) investigate patterns of inbreeding. We find that the conservation of a single population , or even several populations, will not prevent the loss of substantial amounts of genomic variation and adaptive capacity. Rather, the conservation of at least eight populations from across the species distribution is necessary to retain 90 % of SNP alleles. We also show that more geographically isolated populations, such as those on islands, have very small contributions to overall diversity and show relatively high levels of inbreeding compared to mainland populations. Our study highlights the importance of conserving multiple genetically distinct populations to effectively conserve genetic diversity in species undergoing widespread declines, and demonstrates the importance of using multiple criteria to inform and prioritise conservation management.
... Alternatively, if exaggerated color expression is under condition-dependent sexual selection [22], then island species may become less colorful because of reduced sexual selection pressure on islands [17,23]. Sexual selection is predicted to be relaxed on islands because of reduced genetic diversity from founder effects [24] and/or reduced parasite pressure [25], diminishing the indirect fitness benefits from extra-pair copulations [26]. The idea of reduced sexual selection pressure on islands is supported by lower extra-pair paternity rates in island species [27]. ...
... Second, differences in habitat may influence ambient light in the environment, so there may be selection for or against ornate plumage given habitatspecific light conditions [35]. Third, island characteristics such as geographic size and isolation (i.e., distance from mainland) may affect the evolutionary trajectory of color evolution by biasing colonization or by limiting population sizes, thereby diminishing or exacerbating genetic drift effects [24]. Finally, macroevolutionary studies often assess higher-level taxonomic processes, but because selection pressures likely vary among families, the directionality of the effects may change at lower taxonomic levels [36,37]. ...
Island environments have the potential to change evolutionary trajectories of morphological traits in species relative to their mainland counterparts due to habitat and resource differences, or by reductions in the intensity of social or sexual selection. Latitude, island size, and isolation may further influence trait evolution through biases in colonization rates. We used a global dataset of passerine plumage color as a model group to identify selective pressures driving morphological evolution of island animals using phylogenetically-controlled analyses. We calculated chromaticity values from red and blue scores extracted from images of the majority of Passeriformes and tested these against the factors hypothesized to influence color evolution. In contrast to predictions based on sexual and social selection theory, we found consistent changes in island female color (lower red and higher blue chromaticity), but no change in males. Instead, island size and distance from mainland and other islands influenced color in both sexes, reinforcing the importance of island physiognomy in shaping evolutionary processes. Interactions between ecological factors and latitude also consistently influenced color for both sexes, supporting a latitudinal gradient hypothesis. Finally, patterns of color evolution varied among families, indicating taxon-specific microevolutionary processes in driving color evolution. Our results show island residency influences color evolution differently between sexes, but the patterns in both sexes are tempered by ecological, island characteristics, and phylogenetic effects that further vary in their importance among families. The key role of environmental factors in shaping bird plumage on islands further suggests a reduced importance of sexual and social factors in driving color evolution.
... A parallel can be drawn from a remote Saharan oasis (south Algeria) isolated from other waterbodies, where diatoms detected via microscopy and sequencing were all cosmopolitan opportunistic species (Gastineau et al., 2021). In addition, smaller areas have lower carrying capacity and their populations are more vulnerable and prone to extinction due to demographic, environmental, or genetic reasons (Frankham, 1997). It is therefore likely that only a few of the species that reach isolated islands are able to survive and that the remaining ones lose levels of genetic variations (Mittelbach et al., 2007). ...
... It is therefore likely that only a few of the species that reach isolated islands are able to survive and that the remaining ones lose levels of genetic variations (Mittelbach et al., 2007). In addition, speciation rates in smaller areas are expected to be lower (Mittelbach et al., 2007) and genotypes that developed in islands and are endemic to them are more likely to become extinct compared to non-endemic ones (Frankham, 1997). ...
The distribution of microorganisms has long been assumed to be cosmopolitan and primarily controlled by the environment, but recent studies suggest that microbes may also exhibit strong biogeographical patterns driven by dispersal limitation. Past attempts to study the global biogeography of freshwater diatoms have always encountered the great difficulty of collecting taxonomically harmonized large‐scale data. However, developments in molecular techniques and DNA metabarcoding provide a unique opportunity to overcome these limitations and to disclose diatom biodiversity at an unprecedented scale and resolution. Here, we assembled DNA metabarcoding data of freshwater benthic diatom communities sampled in seven geographic regions across the world to investigate how diatom diversity varies along latitude and to assess the proportion of genetic variants of these microorganisms which are exclusive or shared across regions. We observed significant differences in assemblages among climate zones and found that genetic richness is not affected by latitude, but by an island effect. The genetic resolution directly impacts the proportion of variants shared across regions; however, the majority of taxa remained specific to a single geographic region. Freshwater diatoms disperse over long distances and across oceans but at rates that allow the appearance of local genetic variants and the regionalization of assemblages. Future work should focus on putting these diversity dynamics into a temporal context, an approach that should be possible by bringing together new sequencing techniques and phylogeography.
... Despite the importance of reverse colonization for tackling the traditional assumption of islands as sinks of biodiversity , how potentially genetically depauperate island populations (Frankham, 1997) can successfully colonize the continent remained unexamined (Bellemain & Ricklefs, 2008). To answer this question, using an integrative phylogenomics approach, we examined reverse colonization not only by means of phylogenetic patterns but also from demographic perspectives, including temporal population size changes, intraspecific gene flow, and introgression. ...
... It has long been assumed that small effective population size of island populations (Frankham, 1997(Frankham, , 2005 lead to low genetic variation and hence a low chance of reverse colonization (Patiño et al., 2015). Our results showed that the ancestral insular population retained a large effective population size, corroborating the recent arguments that the insular population is not necessarily genetically depauperate (García-Verdugo et al., 2015;Patiño et al., 2015). ...
Islands as biodiversity sinks due to their small population size and low genetic variation are recently challenged by a phenomenon where a continental lineage originates from islands. This raises an important question about through what demographic processes insular genetic variation is introduced to the continent and its evolutionary consequences on the continent. We address this question by focusing on an Asian rail species, the Swinhoe’s Rail Coturnicops exquisitus , where frequent trans-oceanic dispersal in a continent-island system is expected. We reconstructed a spatiotemporally explicit demographic history of this species in the continent-island system, using integrative phylogenomics. Multiple lines of evidence supported asymmetric gene flow from an island population to the continental population that once diverged around the Middle Pleistocene. This has possibly impacted the continental genetic variation because ancient genetic variation may have been preserved in the large island population. Re-establishment of the island by the continental population was also detected, suggesting that the insular genetic variation has been maintained also by receiving a part of continental genetic variation. These results indicated that the maintenance of insular genetic variation through dynamic continent-island metapopulation may have allowed the island to act as a genetic reservoir for continental genetic variation.
Teaser text
What process allows island populations that are small and at the “evolutionary dead-end” to become the source of continental colonization? Using a cutting-edge integrative phylogenomics approach, we disentangled the demographic history of the little-studied Swinhoe’s Rail in East Asia, where it has survived by maintaining a dynamic metapopulation across a continent-island system. Particularly, gene flow from the island impacted the contemporary genetic variation of the continental population, possibly facilitating its demographic expansion. We suggested that maintenance of metapopulation and asymmetric gene flow from islands are key for islands to introduce their genetic variation to the continent.
... We then investigated the patterns of exon sequence diversity and structure across seven contemporary populations (three natural and four translocated) as well as seven historical specimens from now-extinct mainland populations . Mainland specimens were anticipated to show higher levels of exon diversity in line with theoretical expectations of lowered genetic diversity following isolation of populations on islands (Frankham, 1997). We use our findings to provide recommendations regarding the use of admixture approaches in future management of remnant and translocated mammal populations. ...
... The combination of small island size (approx. 45 km 2 ) and regular population crashes in response to declining climatic conditions are likely to cause strong genetic drift, driving rapid genetic differentiation as observed in our analyses of genetic structure (Frankham, 1997;Kimura, 1983;Mills et al., 2004). In the exon capture PCoA, the central position of the historical mainland animals relative to island populations suggests that the former carry ancestral variation now differentially fixed in the latter. ...
Translocation programmes are increasingly being informed by genetic data to monitor and enhance conservation outcomes for both natural and established populations. These data provide a window into contemporary patterns of genetic diversity, structure and relatedness that can guide managers in how to best source animals for their translocation programmes. The inclusion of historical samples, where possible, strengthens monitoring by allowing assessment of changes in genetic diversity over time and by providing a benchmark for future improvements in diversity via management practices. Here, we used reduced representation sequencing (ddRADseq) data to report on the current genetic health of three remnant and seven translocated boodie ( Bettongia lesueur ) populations, now extinct on the Australian mainland. In addition, we used exon capture data from seven historical mainland specimens and a subset of contemporary samples to compare pre‐decline and current diversity. Both data sets showed the significant impact of population founder source (whether multiple or single) on the genetic diversity of translocated populations. Populations founded by animals from multiple sources showed significantly higher genetic diversity than the natural remnant and single‐source translocation populations, and we show that by mixing the most divergent populations, exon capture heterozygosity was restored to levels close to that observed in pre‐decline mainland samples. Relatedness estimates were surprisingly low across all contemporary populations and there was limited evidence of inbreeding. Our results show that a strategy of genetic mixing has led to successful conservation outcomes for the species in terms of increasing genetic diversity and provides strong rationale for mixing as a management strategy.
... Finally, we expected that genetic diversity would be lowest for island populations (Carmichael et al., 2007;Frankham, 1997;Patiño et al., 2017) and that this island effect would exacerbate the negative effects of distance and latitude on genetic diversity by further reducing dispersal and gene flow. ...
... Wolves can swim across open water (Stronen et al., 2014) and travel long distances across frozen water bodies Mech & Dean Cluff, 2011). Nevertheless, we found that island groups exhibited less genetic diversity than did mainland groups, consistent with previous studies of wolves (Adams et al., 2011;Carmichael et al., 2008;Hedrick et al., 2014;Räikkönen et al., 2009;Robinson et al., 2019) and other species (see review by Frankham, 1997). Our results add to this body of knowledge by demonstrating how the detrimental F I G U R E 3 Effects of geographic isolation (distance to species' sampled range center in kilometers and island habitation) on the allelic richness (AR) (a) and expected heterozygosity (H e ) (b) of 2421 wolves from 24 groups across northern North America. ...
Genetic diversity is theorized to decrease in populations closer to a species' range edge, where habitat may be suboptimal. Generalist species capable of long‐range dispersal may maintain sufficient gene flow to counteract this, though the presence of significant barriers to dispersal (e.g., large water bodies, human‐dominated landscapes) may still lead to, and exacerbate, the edge effect. We used microsatellite data for 2421 gray wolves (Canis lupus) from 24 subpopulations (groups) to model how allelic richness and expected heterozygosity varied with mainland–island position and two measures of range edge (latitude and distance from range center) across >7.3 million km² of northern North America. We expected low genetic diversity both at high latitudes, due to harsh environmental conditions, and on islands, but no change in diversity with distance to the range center due to the species' exceptional dispersal ability and favorable conditions in far eastern and western habitats. We found that allelic richness and expected heterozygosity of island groups were measurably less than that of mainland groups, and that these differences increased with the island's distance to the species' range center in the study area. Our results demonstrate how multiple axes of geographic isolation (distance from range center and island habitation) can act synergistically to erode the genetic diversity of wide‐ranging terrestrial vertebrate populations despite the counteracting influence of long‐range dispersal ability. These findings emphasize how geographic isolation is a potential threat to the genetic diversity and viability of terrestrial vertebrate populations even among species capable of long‐range dispersal.
... The level of genetic diversity of both island populations is slightly higher than the mainland counterpart although not significantly. Generally, one can expect that island populations present lower genetic diversity than mainland counterparts [84,85]. Nevertheless, this is not the rule for all taxonomic groups, particularly for bird species where a study suggested that island and mainland bird species did not present a difference in genetic variation [86]. ...
... Nevertheless, this is not the rule for all taxonomic groups, particularly for bird species where a study suggested that island and mainland bird species did not present a difference in genetic variation [86]. Also, in species that can fly, such as birds, there is a less important heterozygosity difference between island and mainland birds [84]. Our results could suggest that the island subspecies, S. p. rufivertex, is well established with probably enough population size to maintain a high level of genetic diversity. ...
The Setophaga petechia complex includes 43 subspecies distributed within the new world, of which some are migratory and others are resident, with only two resident subspecies in the Mexican Caribbean: Setophaga petechia bryanti a mangrove subspecies belonging to the erithachorides group resident on the mainland of the Yucatan Peninsula and Setophaga petechia rufivertex endemic to Cozumel Island and belonging to the petechia group. Recently, a new population of individuals presenting intermediate phenotypic traits and living in mangrove ecosystems was discovered and reported for Cozumel Island. In this study, we used a multi-character approach including genetic (five ISSR genetic markers), morphometric (eight traits), phenotypic (four characteristics of males), and acoustic dataset (11 parameters) to understand the process of differentiation and the status of these new island individuals in relation to the two well-established subspecies using a total of 60 individuals (20 for each group). Through multivariate analyses based on different dataset used in our study, we show how the new population is related to the endemic island subspecies, S. p. rufivertex and to the mainland subspecies, S. p. bryanti while demonstrating finite differences. We conclude that the new population of S. petechia on Cozumel Island is a well-established population with high level of differentiation.
... Translocation events act as a bottleneck and lead to founder effects where a sudden decrease in the number of individuals results in a loss of genetic diversity (Mock et al. 2004;Cardoso et al. 2009). Over time, genetic diversity can be increased through mutation or gene flow, but this process is generally slow, especially on islands where natural gene flow from the mainland is uncommon (Frankham 1997). This result suggests one of the following scenarios: an endemic refugial population of mountain goats existed on Baranof prior to translocation as was previously hypothesized by Shafer et al. (2011b); additional (undocumented) translocation events have occurred; or mountain goats naturally dispersed to Baranof Island after the Wisconsin glaciation but before 1923. ...
Both natural and anthropogenic forces can play a substantial role in the demographic history and current structure of a wildlife population. Species with strict habitat requirements are especially susceptible to these impacts. Mountain goats (Oreamnos americanus) in Alaska are of particular interest in this regard due to their influence on alpine ecosystems, importance to human cultures, and enigmatic history in some areas. Here, we used genetic tools to examine the population structure and demographic history of mountain goats in Alaska. We genotyped 816 mountain goats at 18 microsatellites, identified the number of genetically distinct subpopulations, and assessed their genetic diversity. We used Bayesian methods to investigate demographic history relative to the known geologic and human history of Alaska, and we simulated human-mediated translocation events onto islands to address the hypothesis that Baranof Island harbored an extant population prior to an early 20th-century introduction. We showed that Alaska has 4 genetically distinct subpopulations of mountain goats. The main demographic split between Southcentral and Southeast Alaska occurred following the retreat of ice after the Last Glacial Maximum. Simulations of translocation events largely aligned with expected genetic diversity patterns of current subpopulations except for Baranof Island which showed greater diversity than the simulation, consistent with the hypothesis of an endemic population prior to the translocation. This study highlights the value of considering both natural and anthropogenic forces when assessing the biogeographic history of a species and provides new insights about the complex demographic history and biogeography of mountain goats in Alaska.
... This pattern was also observed in H. quelpaertensis, a salamander on the Korean Peninsula [26]. Generally, mainland populations usually display higher genetic diversity than island populations [27]. ...
Understanding the genetic diversity patterns of endangered species is crucial for biodiversity conservation. The endangered salamander Hynobius yiwuensis, endemic to the mainland and Zhoushan Island in Zhejiang, China, has suffered from sharp population declines due to habitat loss. However, the levels and patterns of genetic diversity, differentiation, and population structure of H. yiwuensis remain poorly understood. Here, we explored the genetic diversity and phylogeography of H. yiwuensis based on partial mtDNA sequences (Cytb and CO1) through 111 individuals collected from seven localities. Relatively high overall haplotype diversity (h = 0.965) and low nucleotide diversity (π = 0.013) were detected. Our results, through phylogenetic trees and haplotype network analyses, revealed two divergent haplogroups, mainland and island, and the estimated divergence time indicated they diverged ~2.44 million years ago, which coincided with the period when Zhoushan Island became separated from the mainland.
... In small, isolated populations, as commonly observed on islands, the interplay between genetic and demographic factors significantly amplifies extinction risk (Frankham, 1997). Islands are frequently subject to disruptive events like droughts or volcanic activity, which can further exacerbate populational bottlenecks (Whittaker and Fernández-Palacios, 2007). ...
Within vertebrates, reptiles are good island colonisers, often leading to considerable levels of intraspecific diversity among populations inhabiting different islands/archipelagos. This study explores the mitochondrial phylogeographic structure of Tarentola boettgeri, a gecko species endemic to the Macaronesian archipelagos of Selvagens and Canary Islands. Our research introduces a novel monophyletic group, comprising the populations from the islands of Selvagem Pequena and Ilhéu de Fora. Furthermore, we confirm the previously identified genetic clusters associated with Selvagem Grande, Gran Canaria and El Hierro. We estimate that the origin of T. boettgeri dates to the upper Miocene (ca. 6.4 Mya), and that the separation of T. boettgeri bischoffi on Selvagem Grande, Selvagem Pequena, and Ilhéu de Fora, occurred ca. 0.5 Mya. The absence of genetic differences between Selvagem Pequena and Ilhéu de Fora suggests recent gene flow or founder events, possibly facilitated by land connections during major glaciations. Conversely, the geographic barriers between Selvagem Grande and Selvagem Pequena likely persisted, preventing genetic admixing. The significant genetic distances observed among all populations underscore the necessity of an integrative taxonomic revision for T. boettgeri. In light of our findings, and with particular consideration of the small population sizes of T. boettgeri bischoffi on Selvagem Pequena and Ilhéu de Fora, we propose that the identified monophyletic groups should be managed as Evolutionarily Significant Units (ESUs). Accordingly, our study highlights the importance of recognizing ESUs in island-restricted reptile populations for targeted conservation efforts, especially given their unique intraspecific diversity and the vulnerability of their habitats.
... Additionally, insular lineages are often subject to environmental disturbances and stochastic events that lead to local extinctions and population reductions (Frankham, 1997). A reduction in effective population size (N e ) will lead to a reduction of its genetic diversity, and ultimately in a reduction of the efficiency of natural selection (Charlesworth, 2009). ...
The ecological and phenotypic diversity observed in oceanic island radiations presents an evolutionary paradox: a high level of genetic variation is typically required for diversification, but species colonizing a new island commonly suffer from founder effects. This reduction in population size leads to lower genetic diversity, which ultimately results in a reduction in the efficiency of natural selection. Then, what is the source of genetic variation which acts as the raw material for ecological and phenotypic diversification in oceanic archipelagos? Transposable elements (TEs) are mobile genetic elements that have been linked to the generation of genetic diversity, and evidence suggests that TE activity and accumulation along the genome can result from reductions in population size. Here, we use the Hawaiian spiny-leg spider radiation (Tetragnatha) to test whether TE accumulation increases due to demographic processes associated with island colonization. We sequenced and quantified TEs in 23 individuals representing 16 species from the spiny-leg radiation and 4 individuals from its sister radiation, the Hawaiian web-building Tetragnatha. Our results show that founder effects resulting from colonization of new islands have not resulted in TE accumulation over evolutionary time. Specifically, we found no evidence for increase in abundance of specific TE superfamilies, nor an accumulation of ‘young TEs’ in lineages which have recently colonized a new island or are present in islands with active volcanoes. We also found that the DNA/hAT transposon superfamily is by far the most abundant TE superfamily in the Tetragnatha radiation. This work shows that there is no clear trend of increasing TE abundance for the spiny-leg radiation across the archipelago chronosequence, and TE accumulation is not affected by population oscillations associated with island colonization events. Therefore, despite their known role in the generation of genetic diversity, TE activity does not appear to be the mechanism explaining the evolutionary paradox of insular diversification in the Tetragnatha spiny-leg radiation.
... The advantages of AGF for wild populations depend on large numbers of introduced individuals providing highly advantageous alleles. However, AGF can be ineffective or even detrimental, and dependent on a wide range of factors, including natural selection, genetic drift, and outbreeding depression [116][117][118][119][120][121][122][123]. To avoid outbreeding depression with fragmented populations by AGF, the pooled genetic diversity from the core metapopulation should be provided. ...
Intergenerational justice entitles the maximum retention of Earth’s biodiversity. The
2022 United Nations COP 15, “Ecological Civilisation: Building a Shared Future for All Life on Earth”, is committed to protecting 30% of Earth’s terrestrial environments and, through COP 28, to mitigate the effects of the climate catastrophe on the biosphere. We focused this review on three core themes: the need and potential of reproduction biotechnologies, biobanks, and conservation breeding programs (RBCs) to satisfy sustainability goals; the technical state and current application of RBCs; and how to achieve the future potentials of RBCs in a rapidly evolving environmental and cultural landscape. RBCs include the hormonal stimulation of reproduction, the collection and storage of sperm and oocytes, and artificial fertilisation. Emerging technologies promise the perpetuation of species solely from biobanked biomaterials stored for perpetuity. Despite significant global declines
and extinctions of amphibians, and predictions of a disastrous future for most biodiversity, practical support for amphibian RBCs remains limited mainly to a few limited projects in wealthy Western countries. We discuss the potential of amphibian RBCs to perpetuate amphibian diversity and prevent extinctions within multipolar geopolitical, cultural, and economic frameworks. We argue
that a democratic, globally inclusive organisation is needed to focus RBCs on regions with the highest amphibian diversity. Prioritisation should include regional and international collaborations, community engagement, and support for RBC facilities ranging from zoos and other institutions to those of private carers. We tabulate a standard terminology for field programs associated with RBCs
for publication and media consistency.
... The advantages of AGF for wild populations depend on large numbers of introduced individuals providing highly advantageous alleles. However, AGF can be ineffective or even detrimental, and dependent on a wide range of factors, including natural selection, genetic drift, and outbreeding depression [116][117][118][119][120][121][122][123]. To avoid outbreeding depression with fragmented populations by AGF, the pooled genetic diversity from the core metapopulation should be provided. ...
Intergenerational justice entitles the maximum retention of Earth’s biodiversity. The 2022 United Nations COP 15, “Ecological Civilisation: Building a Shared Future for All Life on Earth”, is committed to protecting 30% of Earth’s terrestrial environments and, through COP 28, to mitigate the effects of the climate catastrophe on the biosphere. We focused this review on three core themes: the need and potential of reproduction biotechnologies, biobanks, and conservation breeding programs (RBCs) to satisfy sustainability goals; the technical state and current application of RBCs; and how to achieve the future potentials of RBCs in a rapidly evolving environmental and cultural landscape. RBCs include the hormonal stimulation of reproduction, the collection and storage of sperm and oocytes, and artificial fertilisation. Emerging technologies promise the perpetuation of species solely from biobanked biomaterials stored for perpetuity. Despite significant global declines and extinctions of amphibians, and predictions of a disastrous future for most biodiversity, practical support for amphibian RBCs remains limited mainly to a few limited projects in wealthy Western countries. We discuss the potential of amphibian RBCs to perpetuate amphibian diversity and prevent extinctions within multipolar geopolitical, cultural, and economic frameworks. We argue that a democratic, globally inclusive organisation is needed to focus RBCs on regions with the highest amphibian diversity. Prioritisation should include regional and international collaborations, community engagement, and support for RBC facilities ranging from zoos and other institutions to those of private carers. We tabulate a standard terminology for field programs associated with RBCs for publication and media consistency.
... Relative to the mainland, K'gari dingoes are characterised by both reduced SNP (this study; Fig. 3c) and microsatellite (Conroy et al. 2021) genetic variation. That an island population supports reduced variation is not unexpected (Frankham 1996(Frankham , 1997. Repeated periods of intensified genetic drift during the original arrival(s) of dingoes to Australia, subsequent local founder events, and anecdotal population declines via 19th century baiting/culling events, all likely contribute to both broad and fine-scale patterns of variation in contemporary populations (Petrie 1995;Cairns et al. 2018Cairns et al. , 2023Conroy et al. 2021;Stephens et al. 2022;Kumar et al. 2023). ...
Small island populations are vulnerable to genetic decline via demographic and environmental stochasticity. In the absence of immigration, founder effects, inbreeding and genetic drift are likely to contribute to local extinction risk. Management actions may also have a greater impact on small, closed populations. The demographic and social characteristics of a species can, however, delay the impact of threats. K’gari, a ~ 1 660 km² island off the Australian east coast and UNESCO World Heritage Site (Fraser Island 1842–2023), supports an isolated population of approximately 70–200 dingoes that represent an ideal opportunity to explore the small island paradigm. To examine temporal and spatial patterns of genetic diversity in this population we analysed single nucleotide polymorphism (SNP) genotype data (72 454 SNPS) for 112 K’gari dingoes collected over a 25-year period (1996 to 2020). Genetic diversity was lower in K’gari dingoes than mainland dingoes at the earliest time point in our study and declined significantly following a management cull in 2001. We did not find any spatial genetic patterns on the island, suggesting high levels of genetic connectivity between socially discrete packs. This connectivity, combined with the social structure and behaviour of dingoes, may act in concert to buffer the population from the impacts of genetic drift in the short term. Nevertheless, a general decline in genetic variation via inbreeding and drift has occurred over the past 20 years which we suggest should be considered in any future management planning for the population. Monitoring patterns of genetic variation, together with a clearer understanding of the social ecology of K’gari dingoes, will aid in the development of measurable genetic targets set over ecologically meaningful timelines, and help ensure continued survival of this culturally important population.
... For Asiatic black bears, genetic diversity of DQB genes in the whole continental population was much higher than that of the Japanese island population. This could be explained by fewer pathogen communities in island populations (Hochberg and Møller 2001;Lobato et al. 2017), and confirmed the prediction that a large majority of island populations would be less genetically diverse than their continental counterparts (Frankham 1997). The size of continental populations was greater than that of the island population, such as about 28,000 individuals occurring in China and 12,000-19,000 in Japan (Garshelis 2020). ...
High polymorphism in major histocompatibility complex (MHC) genes plays an essential role in adaptive immune response
among vertebrates through antigen recognition and presentation. For vulnerable Asiatic black bear, a lack of DQB gene
sequences from continental populations hindered further genetic diversity analysis in a large geographical region. Here, we
used PCR cloning and sequencing to characterize genetic diversity of DQB gene among diferent populations of the species.
Trans-species polymorphism (TSP) and selective strength of DQB gene were assessed by sequence analysis in Ursidae.
Forty-seven novel Urth-MHC haplotypes, including 32 putative functional alleles (PFA, Urth-DQB*33–Urth-DQB *64)
and one presumed pseudogene (Urth-DQB*65), were identifed in the population. Allelic frequency varied greatly (Urth�DQB*4601 had the highest value) and number of rare alleles was high (34.04%). This might suggest a risk of allele loss by
inbreeding and genetic drift if the efective populations continue to be subdivided and decline without appropriate conserva�tion strategies. In the southern continental population (captive animals), the total number of alleles and population-specifc
alleles were higher than those in the northern. This suggested the southern continental population was exposed to various
pathogens and close conservation attention is required to keep the population safe. Based on values of Hd, π, and K, genetic
diversity of the island population was lower when compared to continental populations. This could be explained by fewer
pathogen communities in island populations, and confrmed the prediction that large majority of island populations would
be less genetically diverse than their continental counterparts. No any allele including those ancestral alleles being similar
among Ursidae species was shared between the continental and island populations. In phylogenetic analysis, DQB alleles did
not show monophyletic for any single species and four alleles were shared among Ursidae. This pattern was TSP. The ratio
(ω=dN / dS) was signifcantly higher than unity on PBR codons (4.029). These features supported the infuence of balanc�ing selection of the DQB locus among continental populations and contributing to the genetic diversity of Urth-DQB. All
codons under positive selection matched the PBR sites inferred by HLA-DQB using four testing methods. Pathogen-driven
positive selection could be the other important mechanism to maintain the advantageous mutation for DQB alleles. This
information will not only promote the understanding of MHC diversity and polymorphism in the Asiatic black bear but will
also increase the implication of protecting vulnerable species in the wild and captive for the appropriate management and
conservation initiatives
... [3][4][5] With high levels of endemism, islands are particularly vulnerable to invasions, driven by characteristics common among island species compared with mainland species, including smaller population sizes, reduced genetic diversity, and lack of defenses against introduced herbivores and predators. [6][7][8] Indeed, more than half of global extinctions have occurred on islands, with invasive species listed as the primary contributors. 2,5 In particular, invasive mammals present the greatest impacts to insular species, primarily through predation. ...
BACKGROUND
Biological invasions are a leading cause of reductions in global biodiversity. Islands are particularly sensitive to invasions, which often result in cascading impacts throughout island communities. Wild pigs ( Sus scrofa ) are globally invasive and pose threats to numerous taxa and ecosystems, particularly for islands where they have contributed to declines of many endemic species. However, the impacts of wild pig diet on the flora and fauna remain understudied in many island systems.
RESULTS
We used DNA metabarcoding of wild pig fecal samples to quantify the seasonal diet composition of wild pigs on three barrier islands in the southeastern USA. Wild pigs exhibited a diverse diet dominated by plants but also including marine and terrestrial animals. The diet composition of plants varied seasonally and between islands. Consumption of invertebrates also changed seasonally, with a shift to coastal invertebrates, particularly crabs, in spring and summer. Vertebrates were found in <10% of samples, but spanned broad taxa including amphibians, fish, mammals, and reptiles. Species consumed by wild pigs indicate wild pigs use a variety of habitats within barrier islands for foraging, including maritime forests, saltmarshes, and beaches.
CONCLUSIONS
An observed shift to beach foraging during sea turtle nesting season suggests wild pigs have potential to hinder nesting success on islands without established management programs. These findings provide insight into the diverse diets of wild pigs on barrier islands and highlight the need for removal of wild pigs from sensitive island ecosystems due to their potential impacts to native plant and animal communities.
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... These species exhibited unexpectedly high levels of genetic diversity (Vega et al. 2007;Espindola et al. 2014). Indeed, genetic diversity is known to be influenced by island size, with larger islands able to harbour a larger number of individuals (Frankham 1997). Accordingly, in Darwin's finches, a significant positive correlation exists between island size (Petren et al. 2005;Brüniche-Olsen et al. 2019). ...
Mus cypriacus is one of three small palaeoendemic mammals that have survived the Mediterranean islands' anthropization. This species, endemic to Cyprus, was described in 2006 and stands out as one of the last mammal species to have been discovered in Europe. Despite scarce data on its genetics, ecology, and life-history traits, Mus cypriacus is assessed as Least Concern LC in the IUCN Red List, partly due to its morphological similarity with the sympatric house mouse that prevented earlier identification. Our study uses mitochondrial and microsatellite markers to investigate this small rodent's population genetic structure and diversity. Our analysis did not identify any population genetic structure and suggested a high genetic diversity across Cyprus. When inferring habitat preference using sample locations, it appeared that M. cypriacus utilizes a diverse variety of habitats, covering more than 80% of the island. Although these results are encouraging for the conservation status of the species, they still need to be cautiously applied as potential threats may arise due to increasing habitat destruction and changes in land use. Consequently, our encouraging results should be applied judiciously. Additional ecological data are urgently needed to gain a more comprehensive understanding of this inconspicuous endemic species.
... As discussed in Ibouroi, Cheha, Arnal, et al. (2018), the low level of genetic diversity found in Anjouan populations can be explained by a limited level of between-island dispersal resulting in strong genetic drift during the island colonisation process and within-island inbreeding, as is the case for many species with low dispersal ability (Haag et al., 2006;Postma & Van Noordwijk, 2005). Frankham (1997) also highlighted that populations from small islands are more susceptible to genetic drift, and tend to show lower levels of genetic diversity than continental populations. ...
Livingstone's fruit bat (Pteropus livingstonii) is among the most threatened bats worldwide. As the species is an important pollinator and seed disperser of Comoros plants with a crucial role in forest regeneration, it is critical to understand how human-induced habitat disturbance impacts genetic structure at fine spatial scales in order to define conservation strategies. In this study, we assessed the level of genetic structure between eight colonies of the species and found that this was strong genetic structures between roosts that can be explained by isolation due both to distance and habitat fragmentation. Mitigation measures should aim to restore population connectivi
... In the short term, when population size declines, the intensification of inbreeding will result in further population declines (Frankham, 1995;Frankham & Ralls, 1998;Frankham, 1999;Brook et al., 2002). Nevertheless, gene flow can prevent the loss of GD in these declining populations, and can help to increase GD in the long run (Frankham, 2010;Frankham, 2015;Ralls et al., 2020), thus affecting the long-term adaptation potential (Frankham, 1997;Franklin & Frankham, 1998;Frankham et al., 2014). The finding of the pronounced quadratic fit between GD and gene flow in endangered species (Fig. 4) suggests that moderate gene flow may be more favorable for maintaining GD in endangered plants over invasive species. ...
Genetic diversity (GD) in populations is important in determining the adaptive potential of populations and is thus thought to influence whether populations decrease or increase in abundance. Yet, a robust evaluation of this premise is needed. By integrating data of 1636 observations from 589 studies globally, we evaluated the relative GD (measured as log response ratio of expected heterozygosity, lnRR) of endangered and invasive plant species compared to control (common or native) species. We also evaluated the variables that influence the variation in population GD within each plant group. Results suggest that the decline in GD is lagging behind the population decline of most endangered plants and that a lower GD did not limit the population expansion of most invasive plants. The effect of inbreeding and gene flow on the relative GD of invasive species was mediated by population size, whereas gene flow directly but nonlinear impacted that of endangered plants, and inbreeding influenced it through an indirect pattern. Mating system was the most important life-history and ecological characteristic to drive relative GD of both endangered plants and invasive plants. The relative GD of endangered plants was also influenced by life form, distribution and rarity form. Overall, genetic diversity was not found to determine species status (endangered or invasive), but species characteristics and genetic factors do have a clear influence on species' evolutionary potential. Understanding the factors that influence GD is key to prioritize management actions on endangered and invasive plants with low and high GD, respectively.
... Populations of Alouatta palliata located in northern latitudes exhibit less genetic diversity than populations located in South America (Cortés-Ortíz et al. 2003;Ford 2006 (Cuarón et al. 2020;Dunn et al. 2014). Previous reports indicate that in general, island populations generally exhibit lower levels of genetic diversity than their mainland counterparts due to isolation, small size and increased inbreeding isolation, small size and increased inbreeding (Frankham 1997;De la Rúa et al. 2001;Jensen et al. 2013;Miller 2010). Compared to other species, A. c. coibensis, although with a small population size, exhibits increased genetic diversity even with other species that show similar habitat conditions, such as the Japanese macaque Macaca fuscata, which inhabits a Japanese island with a similar surface to Coiba´s (504.9 km 2 ) but with a higher population density (Hayaishi & Kawamoto 2006;Méndez-Carvajal 2012). ...
Studies on genetic diversity are key to conservation management because they may determine the resilience of primate populations under environmental and anthropogenic changes. Herein, we studied genetic diversity and connectivity in a population sample of the Coiba island howler monkey Alouatta coibensis coibensis from Coiba island in Panama. We collected 14 faecal samples from individuals at two sites on the northern and north-eastern sides of the island at the Gambute and Los Pozos trails, respectively. DNA was extracted from these samples, and partial sequences of cytochrome oxidase I (COI) were obtained and used as molecular markers to determine genetic diversity. Haplotypic diversity estimates ranged from 0.68 to 0.80 and from 0.0026 to 0.0041 for nucleotide diversity. Genetic connectivity based on reduced genetic distances and nonsignificant Hudson Snn test values suggests elevated connectivity between sites and the existence of a single population with good variability. Demographic history data identified positive Tajimas D as an indication of population contraction and reduced population size in this species. These results will be the baseline for establishing a better understanding of population structure, genetic health, connectivity patterns and reproductive behaviour along the largest island of the Central American Pacific. This information will allow scientists to understand and better evaluate the conservation status of this primate, confirming good availability of genetic flow even for this population living in isolation.
... The species' arrival to a remote oceanic island entails a strong founder event, which inevitably depletes genetic variation (Cerca et al. 2023b). Additionally, insular lineages are often subject to environmental disturbances and stochastic events that lead to local extinctions and population reductions (Frankham 1997). A reduction in effective population size (N e ) will lead to a reduction of its genetic diversity, and ultimately in a reduction of the efficiency of natural selection (Charlesworth 2009). ...
The ecological and phenotypic diversity observed in oceanic island radiations presents an evolutionary paradox: a high level of genetic variation is typically required for diversification, but species colonizing a new island typically suffer from founder effects. This reduction in population size leads to a reduction in genetic diversity, which ultimately results in a reduction in the efficiency of natural selection. Then, what is the source of genetic variation which acts as the raw material for ecological and phenotypic diversification in oceanic archipelagos? Transposable elements (TEs) are mobile genetic elements that have been linked to the generation of genetic diversity, and evidence suggests that TE activity and accumulation along the genome can result from reductions in population size. Here, we use the Hawaiian spiny-leg spider radiation ( Tetragnatha ) to test whether TE accumulation increases due to demographic processes associated with island colonization. We sequenced and quantified TEs in 23 individuals from the spiny-leg radiation and 4 individuals from its sister radiation, the Hawaiian web-building Tetragnatha . Our results show that founder effects resulting from colonization of new islands have not resulted in TE accumulation over evolutionary time. Specifically, we found no evidence for increase in abundance of specific TE superfamilies, nor an accumulation of ‘young TEs’ in lineages which have recently colonized a new island or are present in islands with active volcanoes. We also found that the DNA/hAT transposon superfamily is by far the most abundant TE superfamily in the Tetragnatha radiation. This work shows that TE abundance has remained constant for the spiny-leg radiation across the archipelago chronosequence, and TE accumulation is not affected by population oscillations associated with island colonization events. Therefore, despite their known role in the generation of genetic diversity, TE activity does not appear to be the mechanism to explain the evolutionary paradox of the insular Tetragnatha spiny-leg radiation.
... Indeed, the 'islands' lineage showed greater genomic diversity within most sites than the ' continent' one, possibly due to a greater ability to adapt genetically to environmental change 23 . The resilience and competitive capacity of the 'islands'' A. marcuzzii might be distinctive, considering that it is the only species observed in all sampled islands so far (T. ...
Marine amphipods are crustaceans that lack a larval phase and consequently have low dispersion rates. Despite that, these crustaceans present a remarkable ability to be transported by rafting on natural floating substrata, especially macroalgae, where they find shelter, food and a mating ground. The species Ampithoe marcuzzii is widely distributed throughout the western Atlantic Ocean. Here, it was used as a model to study seascape genomics and phylogeography in invertebrates with low dispersion capacities. We anticipated that the lineages would present isolation-by-distance patterns. However, surface currents and other abiotic variables could facilitate connectivity among distant sites. Based on mitochondrial and nuclear genes, SNPs, and environmental associations, we observed the presence of a species complex within A. marcuzzii, separating mainland and insular populations. Each species showed an independent evolutionary history, with a strong latitudinal population structure and evidence of isolation-by-distance and isolation-by-environment, characterizing the 'continent' species. Historical expansion and environmental variables were observed associated with the southeastern population, and ecological niche modeling corroborated the region as a paleorefuge. Conversely, populations from 'islands' presented complicated evolutionary histories, with closer localities genetically isolated and distant localities connected. These findings indicate that insular populations with low dispersion capacity might be more susceptible to spatial connectivity by floating substrata and to changes in surface currents. In contrast, mainland populations might be more vulnerable to local climate changes due to lack of gene flow.
... insect-based pollination on the mainland) to ornithophily or saurophily (after its colonization to islands) could also promote evolutionary changes on floral traits exerted by these new pollinators (Cronk & Ojeda, 2008; Abrahamczyk, 2019; see also Shrestha et al., 2016 for evolution of floral traits in an island with a predominately or exclusively dipteran pollinator fauna). This can be especially advantageous for insular plants, whose gene pool is often limited (Frankham, 1997). For example, it is known that both specialist and generalist birds promote gene flow among plants through their pollination behaviours, facilitating the transfer of pollen over greater distances compared to bees (Bezemer et al., 2016;Gamba & Muchhala, 2022). ...
Many insular plant species inhabiting different archipelagos worldwide present typical ornithophilous floral traits (e.g. copious nectar, red‐orange colours), but most of them are visited by insectivorous/granivorous birds and lizards, which act as generalist pollinators. Oceanic islands promote these ecological interactions mainly due to the scarcity of arthropods. Our goal is to understand how these generalist interactions contribute to the shift of floral traits from entomophily (mainland) to ornithophily or saurophily (island), where specialist nectar‐feeding birds have not inhabited.
We used the well‐known pollination interactions occurring in the Canary Islands to evaluate two proposed ecological hypotheses, bee‐avoidance or bird‐attraction, explaining evolutionary transitions of floral traits. Specifically, we studied the flower colour conspicuousness of bird‐pollinated Canarian species visited by birds and lizards with their closest relatives from the mainland mainly visited by bees. We analysed the chromatic contrast of flower colours using visual models of bees, birds and lizards and the achromatic contrast in visual models of bees. We also compared reflectance spectra marker points of flowers with available spectral discrimination sensitivities of bees and birds.
Using a phylogenetically corrected framework of independent plant lineages, our results revealed that bird‐pollinated Canarian species showed lower chromatic contrast according to bees and lizard visual models than their mainland relatives, but similar chromatic contrast for bird vision. In addition, reflectance spectra marker points of the Canarian species were displaced to the longest wavelengths, far from the wavelengths of maximum discrimination of bees, but close to birds.
We conclude that the avoidance of bees would be a primary ecological strategy explaining the evolutionary transitions of flower colours from melittophily to ornithophily. The lower conspicuousness of bird‐pollinated Canarian flowers in lizards is perhaps a side effect of the bee‐avoidance strategy rather than an independent evolutionary strategy. Together, these findings provide insights into how vertebrate generalist pollinators can also lead to divergence of floral traits in insular habitats, but also in other arthropod‐poor habitats.
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... Theoretical population genetics predicts that small populations should experience reduced genetic diversity in comparison to bigger ones (Wright, 1938) and exhibit high demographic stochasticity and low-standing genetic variation (i.e., the genetic variants available for the action of the natural selection), factors that hamper their survival over time (Frankham, 1995;Jensen et al., 2007). Small isolated populations are expected to show stronger genetic drift effects with rapid loss of heterozygosis than bigger ones, which is a consequence of their reduced effective population sizes (Kimura, 1983;Frankham, 1997). Small populations are also expected to exhibit high inbreeding values and high rates of slightly disadvantageous mutations (Hoffmann, Sgr o, & Kristensen, 2017;Verena et al., 2020;Leroy et al., 2021;Jackson et al., 2022;Martin et al., 2023). ...
Determining the effectiveness of conservation actions is a priority in conservation biology, especially in island ecosystems which can host large numbers of endemic and often threatened species. In this study, we have brought together a genetic, body condition and breeding success assessment with the aim of evaluating the viability of a newly founded population of the endangered Gran Canaria blue chaffinch ( Fringilla polatzeki ), the forest passerine species with the most restricted distribution in the Western Palearctic. The species occurs exclusively in the Canary pine forests ( Pinus canariensis ) of the island of Gran Canaria, with the Inagua nature reserve harbouring the highest number individuals. In 2010, a translocation program was initiated within the same island in the nearby pine forests of La Cumbre with the goal of establishing a viable breeding population. Genetic results revealed that La Cumbre shows genetic parameters (diversity, inbreeding, and relatedness) similar to the core source of Inagua, which contrasts with the reduced genetic diversity expected due to the small size of the newly founded population. The biometric and body condition results (wing and tarsus length, body mass, and length asymmetry of the tail feathers), together with the breeding success (nest survival and number of fledglings per successful breeding attempt), were also similar in both populations. Overall, these findings suggest that the translocation program has been successful and provide insights on the effectiveness of the actions performed. Our evaluation also delivers future avenues for the conservation planning in other upland forest endangered avian species inhabiting island ecosystems, especially those threatened by the effects of global warming.
... Because small, isolated populations tend to be more prone to extinction (e.g., Paulay 1994;Todd et al. 2010) and to have lower genetic variability (e.g., Frankham 1997Frankham , 2005, studies on island organisms focusing on population size and genetic diversity are important for conservation. However, there are only a few studies focusing on these aspects for island snakes. ...
Snakes have a successful and pervasive presence on islands, and in many cases populations of snakes on islands are robust. Like many other insular biota, snakes can be sensitive to disturbance and extinction. Insular snakes also exhibit, in general, endemic, interesting, and unusual species and are exemplars of evolutionary adaptation and plasticity of responses to new or changing environments, especially prey. Because of the isolation and size of islands, insular snakes can be models for studies of diversification and extinction. In this chapter, the authors assess the success of snake populations on islands and summarize the threats to extant insular species. The authors believe it is imperative that increasing attention be given to conservation of insular snakes and the islands on which they live. They propose that conservation of these species is important for aesthetic, cultural, and scientific values in addition to other reasons discussed in this chapter and volume.
... The smaller effective population size and restricted gene flow result in island species having a high risk for inbreeding, population decline and an increases probability of local extinction (Frankham, 1997(Frankham, , 1998Keller & Waller, 2002). At present, researches on the natural history of island birds revealed their characteristics evolutionary changes. ...
Island endemic birds account for the majority of extinct vertebrates in the past few centuries. To date, the evolutionary characteristics of island endemic bird's is poorly known. In this research, we de novo assembled a high‐quality chromosome‐level reference genome for the Swinhoe's pheasant, which is a typical endemic island bird. Results of collinearity tests suggest rapid ancient chromosome rearrangement that may have contributed to the initial species radiation within Phasianidae, and a role for the insertions of CR1 transposable elements in rearranging chromosomes in Phasianidae. During the evolution of the Swinhoe's pheasant, natural selection positively selected genes involved in fecundity and body size functions, at both the species and population levels, which reflect genetic variation associated with island adaptation. We further tested for variation in population genomic traits between the Swinhoe's pheasant and its phylogenetically closely related mainland relative the silver pheasant, and found higher levels of genetic drift and inbreeding in the Swinhoe's pheasant genome. Divergent demographic histories of insular and mainland bird species during the last glacial period may reflect the differing impact of insular and continental climates on the evolution of species. Our research interprets the natural history and population genetic characteristics of the insular endemic bird the Swinhoe's pheasant, at a genome‐wide scale, provides a broader perspective on insular speciation, and adaptive evolution and contributes to the genetic conservation of island endemic birds.
... Islands have provided supporting evidence for quintessential theories on community ecology, evolution and genetics (Williams 1969, Frankham 1997, Hanski 2001. Patterns of species radiation on islands have driven classical theories in ecology (MacArthur & Wilson 1967, Simberloff 1976, and novel insights have also emerged as processes involved with community assembly are integrated into island biogeography studies (e.g. ...
Islands, critical environments for marine biodiversity, have endorsed several classical ecological theories. However, most studies on marine communities in islands are restricted to oceanic settings; whether premises of island biogeography apply to coastal islands is still unknown. In the Gulf of Thailand (GoT), coral reefs occur in nearshore coastal islands, subject to a wide range of environmental conditions, diverging from the most-studied oceanic counterparts. We investigated fish communities of 51 reefs at 10 sites spanning ~1500 km of the GoT coast, to answer whether diversity and species composition were (1) more influenced by area and isolation than by local environmental conditions and/or (2) affected by the geographical position. As predicted by island biogeography models, diversity decreased with island isolation, albeit only for rare species; reef area increased diversity but solely for common and dominant species. The effect of the geographical position of reefs within the GoT was negligible. Small-scale differences in local conditions of turbidity and depth affected diversity and composition more than isolation and SST. Within-island variability in these conditions yielded a high local turnover of species, enhancing within-site gamma richness, even when the mean alpha richness per site was low. Trophic group composition was similar among most sites, but extreme conditions of environmental constraints (e.g. very high/low turbidity) rendered changes in the dominant trophic group. Results suggest that island biogeography models apply to the reef fish communities in coastal islands to some extent, but the broader ranges of local conditions are the primary drivers of their diversity and composition.
... In conjunction with such life history, physiological and behavioural changes, spatial equilibrial processes (founder effects, restricted dispersal, small population sizes, higher extinction rates) should theoretically reduce the neutral genetic diversity of island populations in comparison to mainland populations. However, while such patterns are predicted, this observation is not generally applicable across all island systems (Frankham 1997, Woolfit and Bromham 2005, García-Verdugo et al. 2015. ...
Spatial isolation is a key driver of population‐level variability in traits and genotypes worldwide. Geographical distance between populations typically increases isolation, but organisms face additional environmental barriers when dispersing between suitable habitat patches. Despite the predicted universal nature of the causes of isolation, global comparisons of isolation effects across taxa and geographic systems are few. We assessed the strength of isolation due to geographic and macroclimatic distance for paired marine island and paired mainland populations within the same species. Our meta‐analysis included published measurements of phenotypic traits and neutral genetic diversity from 1608 populations of 108 plant and animal species at a global scale. As expected, phenotypic differentiation was higher between marine islands than between populations on the mainland, but we found no consistent signal for differences in spatial patterns of neutral genetic diversity between the two systems. Geographic distance had comparatively weak effects on the spatial patterns of phenotypes and neutral genetic diversity. These results suggest that spatial patterns of phenotypic variation are determined by eco‐evolutionary pressures that differ more between islands than between mainland populations, while the spatial variability of neutral genetic diversity might be shaped by rather similar processes in the two systems. Our approach demonstrates that global biodiversity models that include island biology studies may progress our understanding of the interacting effects of spatial habitat structure, geographic‐ and environmental distances on biological processes underlying spatial population variability. We formulate future research directions for empirical tests and global syntheses in the field.
... Leiopelma frogs have already suffered severe range reduction and population fragmentation, which likely caused multiple genetic bottlenecks as the species' population size and range declined in response to habitat loss and predation by introduced species (Easton 2018). This poses a particular risk to L. hamiltoni, since relict island populations have often been shown to have genetic variation reduced further than populations of the same species on the mainland (Frankham 1997;Boessenkool et al. 2007;Cardoso et al. 2009). Populations of Leiopelma have low genetic diversity compared with other anurans (Green 1994;Clay et al. 2010;Easton 2018). ...
... Jersey cattle, which were originally restricted to the Jersey island, suffer from high inbreeding and low genetic diversity rates, which is seen even among animals not kept on the islands anymore (Huson et al., 2020). Lower genetic diversity is expected for insular than for continental populations (Frankham, 1997). Yakut, in contrast, is an ancient breed from Siberia, known for its adaptation to extreme low temperatures. ...
... On the other hand, several traits within a landrace are uniform and can be used for identification [68]. Moreover, since an Fst value greater than 0.15 is considered significant in differentiating populations [69], the value observed in our study (0.51) implies a considerable degree of differentiation among the accessions studied, especially when combined with low levels of gene flow. ...
The genetic diversity of 27 garlic accessions (local varieties/landraces) was investigated using five simple sequence repeat (SSR) and six inter-simple sequence repeat (ISSR) markers. The SSR genotyping revealed 26 different alleles, while 84 polymorphic bands were produced using the ISSR markers. The average polymorphism information content (PIC) was 0.471 and 0.465 for the SSR and the ISSR markers, respectively. Compared to ISSRs, SSR markers revealed a higher level of redundancy, indicating potential duplicates among the accessions. The analysis of molecular variance (AMOVA) based on both marker systems showed that most of the molecular diversity was attributable to differences within accessions, rather than among them. UPGMA, STRUCTURE, and Principal Coordinate Analysis (PCoA) based on the SSRs produced similar clustering results, although not in agreement with those produced by the ISSR markers. Fisher’s exact tests and multinomial logistic regression analyses identified significant associations between the chemical compounds, the morphological traits of the bulb, and specific SSR and ISSR loci. Our results provide a molecular basis for understanding the genetic diversity of Greek garlic landraces, which could be useful for the conservation and sustainable management of this crop. Potential markers fostering the selection of genotypes in garlic breeding have also been revealed.
... It is well documented that isolation and/or large demographic declines affect the ability of a population to maintain genetic diversity over time due to genetic drift (Frankham, 1997;Keller and Waller, 2002). Genetic studies have shown that the current Mednyi population indeed displays low variability (Ploshnitsa et al., 2012;Prôa and Nanova, 2020), a probable consequence of the bottleneck in the 1970s (Ploshnitsa et al., 2012) or of being isolated for such a long period. ...
... High haplotype and nucleotide diversities were observed in the subpopulations of East Malaysia (Sabah and Sarawak) for CO1, ITS2, and the combined sequences. This hypothesis needs further attention because low genetic diversity is the typical characteristic of insects in island populations [41][42][43]. The haplotypes of An. latens were separated into two clusters for all three haplotype networks. ...
Although Malaysia is considered free of human malaria, there has been a growing number of Plasmodium knowlesi cases. This alarming trend highlighted the need for our understanding of this parasite and its associated vectors, especially considering the role of genetic diversity in the adaptation and evolution among vectors in endemic areas, which is currently a significant knowledge gap in their fundamental biology. Thus, this study aimed to investigate the genetic diversity of Anopheles balabacensis, Anopheles cracens, Anopheles introlatus, and Anopheles latens-the vectors for P. knowlesi malaria in Malaysia. Based on cytochrome c oxidase 1 (CO1) and internal transcribed spacer 2 (ITS2) markers, the genealogic networks of An. latens showed a separation of the haplotypes between Peninsular Malaysia and Malaysia Borneo, forming two distinct clusters. Additionally, the genetic distances between these clusters were high (2.3-5.2% for CO1) and (2.3-4.7% for ITS2), indicating the likely presence of two distinct species or cryptic species within An. latens. In contrast, no distinct clusters were observed in An. cracens, An. balabacensis, or An. introlatus, implying a lack of pronounced genetic differentiation among their populations. It is worth noting that there were varying levels of polymorphism observed across the different subpopulations, highlighting some levels of genetic variation within these mosquito species. Nevertheless, further analyses revealed that all four species have undergone demographic expansion, suggesting population growth and potential range expansion for these vectors in this region.
... Here, lower species richness and density compensation (MacArthur et al., 1972;Ribon & Marini, 2016) drives an increase in intraspecific competition relative to diffuse/interspecific competition, which results in selective pressure for adaptations that confer a competitive advantage to individuals that can exploit a wider array of available resources and habitats . At the same time, genetic mechanisms that lead to the evolution of narrow, specialized foraging niches tend to be suppressed on small islands (Johnson & Seger, 2001;Gossmann et al., 2012;Leroy et al., 2021) because small populations tend to have low genetic diversity (Frankham, 1997;, a high degree of population mixing across environmental gradients (Kekkonen et al., 2011;Costanzi & Steifetten, 2019), and because effects of neutral genetic drift are strong compared to adaptive selection (Kimura, 1983;Gossmann et al., 2012;Rousselle et al., 2020). Cumulatively, these conditions result in selection favouring greater phenotypic plasticity and/or behavioural, morphological, or physiological changes that facilitate broader habitat occupancy and wider foraging niches within or among individuals, a phenomenon commonly referred to as "ecological release" (Van Valen, 1973;. ...
Knowledge of species habitat requirements, movements, and life cycles is important for understanding their ecology and functions in ecosystems, and is critical for enabling their effective conservation and monitoring, particularly in small-island states where conservation resources are limited. Island biogeography and ecological release theories make broadly supported predictions about the evolution of generalist traits among small-island birds in the Caribbean, and this research examines the influence of small-island conditions on the life cycle adaptations, diets, and distribution of birds and their responses to human land-use such as agriculture to inform conservation research and management. Using mist-netting, I found that 10 common terrestrial bird species on Grenada (3 endemic to the East Caribbean) exhibited similar patterns of low breeding period seasonality, followed by synchronized peaks in moult intensity and uncommonly high rates of moult-breeding overlap during peak rainfall and high arthropod abundance, despite the wide range in size, morphology, and phylogeny of these species. I studied patterns of seasonal diet composition and diet-overlap among species using DNA meta-barcoding of feces, which suggested that moult-breeding overlap may result from restricted time periods over which arthropod availability is sufficient for breeding and moult to occur. Diet analyses also indicated that agricultural habitats provide important year-round food sources. Lastly, repeated point-count surveys indicated increased bird diversity and abundance at high elevations and in closed-canopy habitats during the dry season, while many birds moved to low elevations and open-canopy habitats in the wet season. Much of Grenada consists of a diverse mosaic of closed-canopy secondary forest patches, interspersed among more open agroforests and small-scale cropping and grazed areas. These agroecosystems appear to provide important habitats and foods to birds throughout the year, especially more-open canopy agroforests in the wet season, while intact canopy forests provide important dry season habitat, which may be particularly important for species in lowland coastal fringe areas experiencing more intensive agricultural, urban, and resort development. This research demonstrates life history adaptations of birds on small islands, the importance of maintaining habitat diversity at local and landscape scales for species conservation, and the contribution of diverse small-scale agroecosystems to supporting small-island bird communities.
... The biota on oceanic islands commonly contains high percentage of endemic species, although their vulnerability is usually greater in relation to continental species due to their restricted and unique geographic distributions, the specificities of their interactions with distinct biotic and abiotic environments, their low resistance to invasion by exotic competitor species and pathogens, and their reduced genetic variability [13][14][15]. These unique features of insular biotas provide ideal configurations for studies of species diversity distributions [16]. ...
The biota on oceanic islands commonly contains high percentage of endemic species, although their vulnerability is usually greater in relation to continental species. Here, we determined the composition, distribution and environmental factors influencing Collembola communities in three coastal environmental habitats of the Fernando de Noronha Archipelago, Brazil. In total, we sampled 20,308 collembolans belonging to 30 species. We report that the sandy beach environments studied harbor a single endemic specialist species (Isotogastrura mucrospatulata Palacios-Vargas, de Lima, & Zeppelini, 2013); environments of slope forest sites and top forests display a generalist fauna with wide distribution on the mainland. In most cases, abundance, richness and diversity did not significantly vary between site, coastal environmental habitat or moisture content levels. However, among the environmental factors, moisture content and litter layer depth were the most important ones structuring the collembolan communities of the archipelago in the DB-RDA analysis. Our results indicate that the beaches of the archipelago harbor completely different collembolan communities from the forests and because they harbor endemic species, and endemic collembolan species have been shown to be more sensitive to disturbance than non-endemics, we also suggest that Sandy Beaches and Slope Forests environments deserve attention in dedicated nature conservation policies as these often are either not soil-specific, or focused on soil physical properties rather than soil biodiversity.
... First, the low genetic diversity of populations located on islands can be attributed to the nature of the islands. In general, reptile species on Diversity 2023, 15, 543 9 of 12 islands have low genetic diversity due to their small population sizes and limited gene flow due to oceanic barriers [59,60]. Our results are consistent with these explanations. ...
The slender racer, Orientocoluber spinalis, is a monotypic species found in northeast Asia. We collected 67 O. spinalis samples from the Republic of Korea (hereafter, South Korea) and 7 from China and Mongolia and investigated their genetic diversity and population structure. In South Korea, O. spinalis populations were mainly found on Oeyeondo, Uido, and Udo islands and Woraksan Mountain and showed low genetic diversity in the analysis of concatenated mitochondrial sequences of the cytochrome b (Cytb) and NADH dehydrogenase subunit 4 (ND4) genes. Orientocoluber spinalis populations in South Korea showed low differentiation and likely diverged recently. Orientocoluber spinalis may have colonized the Korean Peninsula from China and Mongolia, but this route is not confirmed due to the lack of samples from the Democratic People’s Republic of Korea and middle eastern China. Considering its extreme rarity, low population density, and low genetic diversity, O. spinalis should be designated an endangered species in South Korea, as it is in Russia, Mongolia, and Kazakhstan.
... Nonetheless, some studies have shown low N e in a range of island organisms (e.g., Loire et al. 2013;Kutschera et al. 2020), and it is plausible that island populations in general exhibit lower N e when compared to mainland species (Leroy et al. 2021). Furthermore, while inbreeding can be common in islands when compared to mainland populations (Frankham 1997(Frankham , 2008, we did not detect any evidence of highly isolated small populations (beyond the main Maria/Southern populations split) that are particularly susceptible to loss of genetic diversity or inbreeding under the current patterns of connectivity, and overall genetic diversity is represented across remaining populations. ...
Genetic data can be highly informative for answering questions relevant to practical conservation efforts, but remain one of the most neglected aspects of species recovery plans. Framing genetic questions with reference to practical and tractable conservation objectives can help bypass this limitation of the application of genetics in conservation. Using a single-nucleotide polymorphism dataset from reduced-representation sequencing (DArTSeq), we conducted a genetic assessment of remnant populations of the endangered forty-spotted pardalote (Pardalotus quadragintus), a songbird endemic to Tasmania, Australia. Our objectives were to inform strategies for the conservation of genetic diversity in the species and estimate effective population sizes and patterns of inter-population movement to identify management units relevant to population conservation and habitat restoration. We show population genetic structure and identify two small populations on mainland Tasmania as 'satellites' of larger Bruny Island populations connected by migration. Our data identify management units for conservation objectives relating to genetic diversity and habitat restoration. Although our results do not indicate the immediate need to genetically manage populations, the small effective population sizes we estimated for some populations indicate that they are vulnerable to genetic drift, highlighting the urgent need to implement habitat restoration to increase population size and to conduct genetic monitoring. We discuss how our genetic assessment can be used to inform management interventions for the forty-spotted pardalote and show that by assessing contemporary genetic aspects, valuable information for conservation planning and decision-making can be produced to guide actions that account for genetic diversity and increase chances of recovery in species of conservation concern.
... This isolation may effectively render the SRM a terrestrial 'island', and island populations are more prone to genetic drift and loss of diversity than populations on a 'mainland' (Cardoso et al., 2009;Eldridge et al., 1999;Frankham, 1997;Mills et al., 2004). ...
Wildlife diseases are a major global threat to biodiversity. Boreal toads (Anaxyrus [Bufo] boreas) are a state-endangered species in the southern Rocky Mountains of Colorado and New Mexico, and a species of concern in Wyoming, largely due to lethal skin infections caused by the amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd). We performed conservation and landscape genomic analyses using single nucleotide polymorphisms from double-digest, restriction site-associated DNA sequencing in combination with the development of the first boreal toad (and first North American toad) reference genome to investigate population structure, genomic diversity, landscape connectivity, and adaptive divergence. Genomic diversity (π=0.00034–0.00040) and effective population sizes (Ne=8.9 –38.4) were low, likely due to post-Pleistocene founder effects and Bd-related population crashes over the last three decades, respectively. Population structure was also low, likely due to formerly-high connectivity among a higher density of geographically-proximate populations. Boreal toad gene flow was facilitated by low precipitation, cold minimum temperatures, less tree canopy cover, low heat load, and less urbanization. We also found >8X more putatively-adaptive loci related to Bd intensity than to all other environmental factors combined, as well as evidence for genes under selection related to immune response, heart development and regulation, and skin function. These data suggest boreal toads in habitats with Bd have experienced stronger selection pressure from disease than from other, broad-scale environmental variation. These findings can now be used by managers to conserve and recover the species through actions such as reintroduction and supplementation of populations that have declined due to Bd.
Fruit bats (genus Pteropus ) are typically island‐endemic species important in seed dispersal and reforestation that are vulnerable to increased extinction risk. An effective method of reducing extinction risk in vulnerable species that cannot be conserved in their native habitat is establishing an ex‐situ captive breeding programme. Due to anthropogenic threats and low population numbers, in the early 1990s, a captive breeding programme was established at Jersey Zoo, British Isles, for Critically Endangered Livingstone's fruit bats ( Pteropus livingstonii ). Here we use six polymorphic microsatellite loci to assess genetic diversity in the captive breeding population of Livingstone's fruit bats ( P. livingstonii ), 30 years after the programme's establishment, investigating change over generations and comparing our findings with published data from the wild population. We found no significant difference between the genetic diversity in the captive and wild populations of Livingstone's fruit bats ( P. livingstonii ), in both expected heterozygosity and allelic richness. The captive population has retained a comparable level of genetic diversity to that documented in the wild, and there has been no significant decline in genetic diversity over the last 30 years. We advise that a full pedigree of the paternal lineage is created to improve the management of the captive breeding programme and further reduce the possibility of inbreeding. However, it appears that the captive breeding programme is currently effective at maintaining genetic diversity at levels comparable to those seen in the wild population, which suggests reintroductions could be viable if genetic diversity remains stable in captivity.
Aim
Our aim was to assess the population structure, genetic diversity and demographic history of the wolverine (Gulo gulo) throughout its entire Eurasian range. Additionally, we aimed to contextualize and put into perspective the state of the endangered Fennoscandian population by emphasizing its connectivity to other populations.
Location
The main study area covered most of the Eurasian wolverine range, with samples from Finland, Russia, Kazakhstan and Mongolia.
Methods
Using a 495 bp fragment of the mitochondrial DNA control region and a frequently used set of 14 microsatellite markers on an extensive dataset of samples, we assessed the population structure, genetic diversity, and demographic history of wolverines with a variety of population genetic analyses.
Results
According to both nuclear and mitochondrial genetic markers, Eurasian wolverines exhibit substructure, with the most distinct population located in Fennoscandia. The Fennoscandian population has undergone a genetic bottleneck, likely influencing its genetic diversity, which is notably the lowest in Eurasia. Genetic diversity in the rest of Eurasia gradually rises towards the central part of the range and decreases again in the east, although not as significantly as in the west.
Main Conclusions
This study reveals the population structure of wolverines across Eurasia and provides direction for allocating conservation efforts to sustain a diverse and connected wolverine population. While most of the Eurasian populations seem to be well‐connected and genetically diverse, the Fennoscandian wolverines may need better connectivity to the other Eurasian populations to ensure gene flow and long‐term persistence. Our study further highlights the importance of considering the population genetic structure and diversity of the entire species range when planning management strategies.
Understanding the factors driving phenotypic and genomic differentiation of insular populations is of major interest to gain insight into the speciation process. Comparing patterns across different insular taxa subjected to similar selective pressures upon colonizing oceanic islands provides the opportunity to study parallel evolution and identify shared patterns in their genomic landscapes of differentiation. We selected four species of passerine birds (common chaffinch Fringilla coelebs/canariensis , red-billed chough Pyrrhocorax pyrrhocorax , house finch Haemorhous mexicanus and dark-eyed/island junco Junco hyemalis/insularis ) that have both mainland and insular populations. For each species, we sequenced whole genomes from mainland and insular individuals to infer their demographic history, characterize their genomic differentiation, and identify the factors shaping them. We estimated the relative (F) and absolute (d) differentiation, nucleotide diversity (π), Tajima’s D, gene density and recombination rate. We also searched for selective sweeps and chromosomal inversions along the genome. Changes in body size between island and mainland were consistent with the island rule. All species shared a marked reduction in effective population size (N) upon island colonization. We found highly differentiated genomic regions in all four species, suggesting the role of selection in island-mainland differentiation, yet the lack of congruence in the location of these regions indicates that each species adapted to insular environments differently. Our results suggest that the genomic mechanisms involved, which include selective sweeps, chromosomal inversions, and historical factors like recurrent selection, differ in each species despite the highly conserved structure of avian genomes and the similar selective factors involved.
Understanding the processes that underlie the development of population genetic structure is central to the study of evolution. Patterns of genetic structure, in turn, can reveal signatures of isolation by distance (IBD), barriers to gene flow, or even the genesis of speciation. However, it is unclear how severe range restriction might impact the processes that dominate the development of genetic structure. In narrow endemic species, is population structure likely to be adaptive in nature, or rather the result of genetic drift? In this study, we investigated patterns of genetic diversity and structure in the narrow endemic Hayden's ringlet butterfly. Specifically, we asked to what degree genetic structure in the Hayden's ringlet can be explained by IBD, isolation by resistance (IBR) (in the form of geographic or ecological barriers to migration between populations), and isolation by environment (in the form of differences in host plant availability and preference). We employed a genotyping‐by‐sequencing (GBS) approach coupled with host preference assays, Bayesian modelling, and population genomic analyses to answer these questions. Our results suggest that despite their restricted range, levels of genetic diversity in the Hayden's ringlet are comparable to those seen in more widespread butterfly species. Hayden's ringlets showed a strong preference for feeding on grasses relative to sedges, but neither larval preference nor potential host availability at sampling sites correlated with genetic structure. We conclude that geography, in the form of IBR and simple IBD, was the major driver of contemporary patterns of differentiation in this narrow endemic species.
Understanding the factors driving phenotypic and genomic differentiation of insular populations is of major interest to gain insight into the speciation process. Comparing patterns across different insular taxa subjected to similar selective pressures upon colonizing oceanic islands provides the opportunity to study parallel evolution and identify shared patterns in their genomic landscapes of differentiation. We selected four species of passerine birds (common chaffinch Fringilla coelebs/canariensis , red-billed chough Pyrrhocorax pyrrhocorax, house finch Haemorhous mexicanus and dark-eyed/island junco Junco hyemalis/insularis) that have both mainland and insular populations. For each species, we sequenced whole genomes from mainland and insular individuals to infer their demographic history, characterize their genomic differentiation, and identify the factors shaping them. We estimated the relative ( F st ) and absolute ( d xy ) differentiation, nucleotide diversity (π), Tajima’s D, gene density and recombination rate. We also searched for selective sweeps and chromosomal inversions along the genome. Changes in body size between island and mainland were consistent with the island rule. All species shared a marked reduction in effective population size (N e ) upon island colonization. We found highly differentiated genomic regions in all four species, suggesting the role of selection in island-mainland differentiation, yet the lack of congruence in the location of these regions indicates that each species adapted to insular environments differently. Our results suggest that the genomic mechanisms involved, which include selective sweeps, chromosomal inversions, and historical factors like recurrent selection, differ in each species despite the highly conserved structure of avian genomes and the similar selective factors involved.
Island organisms often evolve phenotypes divergent from their mainland counterparts, providing a useful system for studying adaptation under differential selection. In the white-winged fairywren (Malurus leucopterus), subspecies on two islands have a black nuptial plumage whereas the subspecies on the Australian mainland has a blue nuptial plumage. The black subspecies have a feather nanostructure that could in principle produce a blue structural color, suggesting a blue ancestor. An earlier study proposed independent evolution of melanism on the islands based on the history of subspecies divergence. However, the genetic basis of melanism and the origin of color differentiation in this group are still unknown. Here, we used whole-genome resequencing to investigate the genetic basis of melanism by comparing the blue and black M. leucopterus subspecies to identify highly divergent genomic regions. We identified a well-known pigmentation gene ASIP and four candidate genes that may contribute to feather nanostructure development. Contrary to the prediction of convergent evolution of island melanism, we detected signatures of a selective sweep in genomic regions containing ASIP and SCUBE2 not in the black subspecies but in the blue subspecies, which possesses many derived SNPs in these regions, suggesting that the mainland subspecies has re-evolved a blue plumage from a black ancestor. This proposed re-evolution was likely driven by a pre-existing female preference. Our findings provide new insight into the evolution of plumage coloration in island versus continental populations, and, importantly, we identify candidate genes that likely play roles in the development and evolution of feather structural coloration.
Movement of animals and plants from mainland populations contributes to the genetic diversity and viability of geographically isolated island biota, but also carries risks of pathogen introductions. The bat fauna of the island of Trinidad reflects species diversity on the neighbouring South American mainland and includes the common vampire bat ( Desmodus rotundus) . We determined relationships between Trinidad and mainland vampire bat populations and the extent of mainland-island movement by comparing the genetic structure (nuclear and mitochondrial) and morphology of the Trinidadian D. rotundus population to populations in neighbouring regions of the South American mainland and estimating evolutionary histories and patterns of gene flow.
Results indicate that Trinidadian D. rotundus are genetically and morphologically distinct from mainland populations, although limited unidirectional male-biased mainland to island gene flow occurs at an estimated rate of 3.3 migrants per year. Two geographically-defined Desmodus cytochrome b clades were identified within Trinidad (i.e., one restricted to the South-Western peninsula which grouped with Venezuelan sequences and the other found throughout the rest of the island which grouped with sequences from Suriname and Guyana) suggesting long-standing female philopatry. The geographic distribution of these clades mirrors that of two previously identified geographically defined rabies virus (RABV) lineages introduced to Trinidad from the mainland. This finding suggests that bat dispersals and RABV introductions occur via both the northern and south-western island peninsulas, with subsequent male-driven intra-island viral spread enabled by bat nuclear homogeneity of these populations. These study findings will contribute to the development of contemporary evidence-based vampire bat population control and rabies prevention programs within island populations.
Wildlife diseases are a major global threat to biodiversity. Boreal toads ( Anaxyrus [Bufo] boreas ) are a state‐endangered species in the southern Rocky Mountains of Colorado and New Mexico, and a species of concern in Wyoming, largely due to lethal skin infections caused by the amphibian chytrid fungus Batrachochytrium dendrobatidis ( Bd ). We performed conservation and landscape genomic analyses using single nucleotide polymorphisms from double‐digest, restriction site‐associated DNA sequencing in combination with the development of the first boreal toad (and first North American toad) reference genome to investigate population structure, genomic diversity, landscape connectivity and adaptive divergence. Genomic diversity ( π = 0.00034–0.00040) and effective population sizes ( N e = 8.9–38.4) were low, likely due to post‐Pleistocene founder effects and Bd ‐related population crashes over the last three decades. Population structure was also low, likely due to formerly high connectivity among a higher density of geographically proximate populations. Boreal toad gene flow was facilitated by low precipitation, cold minimum temperatures, less tree canopy, low heat load and less urbanization. We found >8X more putatively adaptive loci related to Bd intensity than to all other environmental factors combined, and evidence for genes under selection related to immune response, heart development and regulation and skin function. These data suggest boreal toads in habitats with Bd have experienced stronger selection pressure from disease than from other, broad‐scale environmental variations. These findings can be used by managers to conserve and recover the species through actions including reintroduction and supplementation of populations that have declined due to Bd .
At the end of the last ice age, several Atlantic salmon populations got caught up in the lakes and ponds of the Northern Hemisphere. Occasionally, the populations also got locked when the flow of rivers terminated from reaching the sea due to land upheaval. Therefore, the pattern of evolution shaping the landlocked salmon populations is different from the other anadromous salmons, which migrate between the sea and rivers. According to the theories of population genetics, the effect of genetic drift is expected to be more pronounced in the former compared to the latter. Here we examined this using the whole genome data of landlocked and anadromous salmon populations of Norway. Our results showed a 50–80% reduction in the genomic heterozygosity in the landlocked compared to anadromous salmon populations. The number and total size of the runs of homozygosity (RoH) segments of landlocked salmons were two to eightfold higher than those of their anadromous counterparts. We found the former had a higher ratio of nonsynonymous-to-synonymous diversities than the latter. The investigation also revealed a significant elevation of homozygous deleterious Single Nucleotide Variants (SNVs) in the landlocked salmon compared to the anadromous populations. All these results point to a significant reduction in the population size of the landlocked salmons. This process of reduction might have started recently as the phylogeny revealed a recent separation of the landlocked from the anadromous population. Previous studies on terrestrial vertebrates observed similar signatures of a bottleneck when the populations from Island and the mainland were compared. Since landlocked waterbody such as ponds and lakes are geographically analogous to Islands for fish populations, the findings of this study suggest the similarity in the patterns of evolution between the two.
Low levels of allozyme heterozygosity in populations are often attributed to previous population bottlenecks; however, few experiments have examined the relationship between heterozygosity and bottlenecks under natural conditions. The composition and number of founders of 55 experimental populations of the eastern mosquitofish (Gambusia holbrooki), maintained under simulated field conditions, were manipulated to examine the effects of bottlenecks on three components of allozyme diversity. Correlations between observed and expected values of allozyme heterozygosity, proportions of polymorphic loci, and numbers of alleles per locus were 0.423, 0.602, and 0.772, respectively. The numbers of polymorphic loci and of alleles per locus were more sensitive indicators of differences in genetic diversity between the pre-bottleneck and post-bottleneck populations than was multiple-locus heterozygosity. In many populations, single- and multiple-locus heterozygosity actually increased as a result of the founder event. The weak relationship between a population's heterozygosity and the number and composition of its founders resulted from an increase in the variance of heterozygosity due to drift of allele frequencies. There was little evidence that selection influenced the loss of allozyme variation. When it is not possible to estimate heterozygosity at a large number of polymorphic loci, allozyme surveys attempting to detect founder events and other types of bottlenecks should focus on levels of locus polymorphism and allelic diversity rather than on heterozygosity.
Small, isolated populations of Melomys cervinipes occur in rainforest framents on the Atherton Tableland, NE Queensland. The authors studied the genetic structure of four of these populations: one island (4.3 ha; isolated in 1960), three fragments (2.5, 7.5, 97.5 ha; isolated between 1920-1930) and a control population in continuous rainforest. Average heterozygosity (H) was estimated from the allelic distribution of 25 loci for each population and varied from 0.01-0.05. The island population had reduced heterozygosity compared to the control population, but the fragment populations were not signficantly less heterozygous than the control. Although the fragment populations were markedly different in size, the did not differ in heterozygosity among themselves. The ability of fragment populations to maintain genetic viability is probably due to migration. The rainforest fragments exist in an extensive grassland containing a variety of habitat corridors which could facilitate movement and gene flow. Presence of M. cervinipes in corridors and its use of the corridors for movement was indeed confirmed. The island population appears to be substantially more isolated than the fragment populations as water is likely to be a much more effective barrier to movement than is heterogeneous grassland. The genetic viability of the island population has probably been reduced through drift, leading to fixation of alleles: six of eight polymorphic loci being fixed in the island population. Retention or establishment of habitat corridors is an important means of sustaining the genetic variability of populations in fragmented systems. -from Authors
Patton, J. L., S. Y. Yang, and P. Myers 1975. Genetic and morphologic divergence among introduced rat populations (Rattus rattus) of the Galápagos Archipelago, Ecuador. Syst. Zool. 24:296–310.—The roof rat (Rattus rattus Linnaeus) was initially introduced into the Galápagos Archipelago before Darwin's visit in 1835. The species is now known
from seven of the 16 major islands and exhibits a wide range in both human and non-human associated habitat usages. Morphological
distinctiveness of island populations was first noted by Heller in 1904, consisting of overall size and shape as well as pelage
color differences. Analyses involving allozyme frequencies at 37 genetic loci, epigenetic cranial characters, and multivariate
treatments of mensural characters confirm and extend these observations. The level of concordance between each analysis is
extremely high; each delineates the same three groupings of islands based on overall similarity: (1) Isla Santiago-Bartolome;
(2) Isla Floreana-Isabela-Pinzón-San Cristóbal; and (3) Isla Santa Cruz-Baltra. An hypothesis of multiple origins best accounts
for the similarity relationships between islands as each of the groupings fits a known separate period of human use activity.
The initial introduction was most likely at Santiago in the late 1600's; the most recent on Baltra-Santa Cruz during World
War II. Gene flow between the different island groups, past and present, is considered slight, but continual introduction
of immigrants from outside source populations, particularly to Baltra, Santa Cruz, and San Cristóbal, is highly probable.
Genie variability as demonstrated by allozyme analysis is quite low (mean heterozygosity = 2.85 per cent) when compared to
other rodent species. The pattern of variability, however, suggests that this low level does not result from a severe founder
effect, but that it is a general characteristic of the species as a whole.
A population of green iguanas (Iguana iguana) that inhabits the forests around Gatun Lake in central Panama faces an apparent scarcity of suitable nesting sites. To investigate whether the disjunct distribution of nesting sites in this area and strong nesting site fidelity by female iguanas has contributed to genetic structuring of the population, samples obtained from females captured at three main nesting sites were analyzed electrophoretically. Significant allele frequency differences existed among nesting sites at one of the two polymorphic loci inspected. The pattern of allele frequency differences was consistent with what is known of iguana movement patterns and suggests that the genetic structure of the population has been influenced by nesting site availability and distribution. Additional electrophoretic analyses were conducted on samples obtained from three iguana populations from central Panama, western Panama, and Venezuela. Low levels of heterozygosity and polymorphism were observed in each of these populations, yet significant differences at three polymorphic loci were demonstrated. The management implications of the results are discussed. /// La población de iguanas verdes (Iguana iguana) que habita en los bosques alrededor al Lago Gatún en Panamá central, encuentra una escasez aparente de lugares específicos para realizar la puesta anual. Muestras de sangre y de músculos fueron obtenidas de las iguanas hembras que fueron capturadas en los tres principales lugares de puesta en esta área y fueron analizadas por electroforesis. Se encontraron diferencias significativas en las frecuencias de los alelos en uno de los dos loci variables que fueron analizados. Aparentemente la distribución esparcida de los lugares de la puesta, y la gran fidelidad de las hembras a éstos, han generado subpoblaciones cuantitativamente distintas, en las áreas que están asociadas con estos lugares de la puesta. Análisis adicionales fueron realizados con muestras de tres poblaciones separadas en Panamá central, Panamá occidental, y Venezuela. La cantidad de heterocigosidad y polimórfismo genético que fue demonstrada en cada población es muy baja con respecto a otras especies de largatijas que han sido investigadas. Dado que existen diferencias poblacionales del comportamiento, de la ecología, y de la genética en esta especie, los proyectos de manejo de la iguana verde deben ser cuidadosos en la selección de los animales que van a introducirse.
We used starch-gel electrophoresis to assess variability at 41 genetic loci in 208 individuals from 11 breeding populations of the Western Flycatcher (Empidonax difficilis) complex. Genic variability was substantial in most populations and equivalent to levels found in other avian taxa. A sample of E. d. insulicola from Santa Catalina Island, however, showed reduced heterozygosity and an unusually low percentage of polymorphic loci. We attribute this to a bottleneck at the time of the original colonization. Nei's genetic distances among populations of one taxon ranged from D̄ = 0.0003 (in E. d. difficilis) to D̄ = 0.0033 (in E. d. hellmayri). Intertaxon Nei's D̄ ranged from 0.009 (E. d. insulicola vs. E. d. difficilis) and 0.0149 (E. d. difficilis vs. E. d. hellmayri) to 0.0228 (E. d. insulicola vs. E. d. hellmayri). to 0.0228 (E. d. insulicola vs. E. d. hellmayri). F statistics revealed significant population subdivision within the complex. With Slatkin's rare-allele method we estimated the gene-flow parameter, Nm. Mainland populations experience moderately high gene flow (9.62 immigrants/generation). In contrast, Santa Catalina Island receives an estimated 0.093 immigrants/generation, pointing to very low gene flow and essential genetic isolation.
Genetic distances yielded phenograms and distance Wagner trees that provide hypotheses for the relationships and phylogenesis of populations in western North America. The lineage leading to modern E. d. difficilis split from that leading to E. flavescens in the mid-Pleistocene at 866,800 yr BP; the ancestors of modern E. d. difficilis diverged from those of present-day E. d. hellmayri at 248,700 yr BP; and the stock leading to modern E. d. insulicola budded from the lineage that became E. d. difficilis in the late Pleistocene, approximately 187,000 yr BP.
Empidonax d. difficilis and E. d. hellmayri nest sympatrically and mate assortatively in the Siskiyou region of northern California. Interbreeding has not been demonstrated conclusively, and we regard these taxa as biologic species. In the absence of a test of sympatry, the well-differentiated form E. d. insulicola of the California Channel Islands cannot be proved to be a biologic species. It is clearly a phylogenetic species, however, in the sense of Cracraft.
Enzyme electrophoresis was employed to measure genetic variation within and divergence among 32 populations of three species in Solanum sect. Petota (S. brevidens, S. etuberosum, and S. fernandezianum). These species are self-compatible, diploid (2n = 2x = 24), and members of the monophyletic series Etuberosa. Solanum etuberosum is distributed in southern Chile, S. brevidens occurs in southern Chile and adjacent southern Argentina, and S. fernandezianum is endemic to Masatierra Island in the Juan Fernández Archipelago, 650 km west of continental Chile. Very low levels of observed heterozygosity (0.00–0.04) are found within populations of all three species. Interspecific mean genetic identities between S. brevidens and S. etuberosum (0.854) were similar to their intraspecific values (0.923, 0.865, respectively), with both species monomorphic for alleles at nine of the 12 loci examined. Solanum fernandezianum shows no heterozygosity and is more divergent to both S. brevidens (0.780) and S. etuberosum (0.698) than either is to each other. The divergence of S. fernandezianum to S. brevidens and S. etuberosum results from novel alleles at two of the 12 isozyme loci; in addition, it possesses only a subset of the variability found in S. brevidens and S. etuberosum at three other loci.
Gossypium hirsutum has a large indigenous range encompassing most of Mesoamerica and the Caribbean, where it exhibits a diverse array of morphological forms spanning the wild-to-domesticated continuum. Modem, highly improved varieties (“Upland cotton”), which currently account for about 90% of world cotton commerce, are day-length neutral annuals derived from subtropical, perennial antecedents. To assess levels and patterns of genetic variation in the species and to elucidate the origin of Upland cotton, 538 accessions representing the full spectrum of morphological and geographical diversity were analyzed forallozyme variation at 50 loci. Levels of variation are modest overall but are low in Upland cotton. Relationships among accessions reflect pre-Columbian influences of aboriginal peoples and later European colonists superimposed on the preagricultural pattern. In contrast to expectations, two centers of diversity are evident, one in southern Mexico-Guatemala and the other in the Caribbean. Introgression of G. barbadense genes into G. hirsutum has been common in a broad area of sympatry in the Caribbean. The germplasm of present cultivars traces to Mexican highland stocks, which, in turn, were derived from material originally from southern Mexico and Guatemala. Despite the widespread belief that germplasm from several other species has been incorporated into modem Upland stocks through intentional breeding efforts, the 50 Upland cultivars examined contain no unique alleles, suggesting that retention of genes from transspecific sources has been minimal. The most recent infraspecific treatment, which recognizes seven races, does not adequately represent genetic relationships.
Gossypium tomentosum is the only member of the cotton genus endemic to the Hawaiian archipelago. It is morphologically distinct from other allopolyploid Gossypium species, and its phylogenetic relationships with them are uncertain. Chloroplast and ribosomal DNA restriction site variation were used to estimate the phylogeny of the allopolyploids. Gossypium mustelinum is resolved as sister to the remaining allopolyploid species, which include two species-pairs, G. barbadense-G. darwinii and G. hirsutum (including G. lanceolatum)-G. tomentosum. This indication that G. tomentosum is sister to G. hirsutum is supported by allozyme data. Gossypium tomentosum is proposed, based on biogeographic evidence and molecular data, to have originated by transoceanic dispersal from a Mesoamerican progenitor. Few restriction site variants were observed among the allopolyploids, suggesting that present lineages diverged relatively rapidly following polyploidization. Allozyme analysis of 30 G. tomentosum accessions collected from seven islands revealed relatively low levels of genetic diversity: 11 of 50 loci were polymorphic, mean number of alleles per locus was 1.24, and mean panmictic heterozygosity was 0.033. Little geographic patterning of allelic distributions was observed. Despite historical cultivation of G. barbadense and G. hirsutum in Hawaii and the existence of their naturalized derivatives, no allozyme evidence of interspecific introgression into G. tomentosum was detected.
Allozyme variation was investigated in 17 Japanese populations of Campanula punctata, ten from the Izu Islands and seven in the mainland (Honshu). The data indicate that there are two groups, a mainland group and an island one, and that the systematically problematic Oshima Island (northernmost Izu island) populations are closely related to those of the other islands. Nei's genetic identity values among islands and among mainland populations were 0.95 and 0.97, respectively, while the value between island and mainland populations was 0.84, suggesting that the island populations are an independent species. Total genetic variation was nearly the same among island and mainland populations. However, the apportionment of variation within and among populations was considerably different; 14% of gene diversity exists among mainland populations, while 31% of the diversity exists among island populations. Mean outcrossing rates of self-incompatible mainland and Oshima populations are 0.62–0.79, supporting xenogamy; those in self-compatible island populations are 0.37–0.57 in the northern islands, indicating a mixed mating system, and 0.16–0.25 in southern ones, indicating dominant inbreeding. Total genetic diversity in each island population decreased with distance from the mainland. Genetic and geological data suggest that the ancestors of insular populations were founded on northern islands in a relatively ancient period and that they dispersed progressively to the southern ones. Chromosome number (2n = 34) and isozyme numbers indicate gene duplications in this species, which suggests it is an ancient polyploid.
Nineteen populations representing all species of Galvezia were examined for electrophoretic differentiation at 23 loci. Allozyme variation within G. leucantha is minimal, suggesting that a genetic bottleneck, possibly resulting from a single colonization event, accompanied establishment of Galvezia in the Galàpagos Islands less than 1.5 million years ago. South American species have higher levels of genetic polymorphism. Interspecific divergence patterns in Galvezia are characterized by many qualitative allelic differences, including one to six marker alleles for each species. Isozyme data support delimitation of four species. Geographic modes of speciation predominate. Allozyme data indicate that the Galàpagos endemic is not a recent derivative from a continental progenitor; rather, it is most likely the sister species to G. fruticosa or to a lineage of G. fruticosa and an undescribed species from southern Peru. It is hypothesized that the presence of six fixed, unique alleles in G. leucantha identifies a relictual genotype from an extinct South American progenitor. Biogeographic patterns and the presence of an allele shared between G. leucantha and two populations from the Sechura Desert indicate that northern Peru is the probable source region for the Galàpagos introduction. Estimates of elapsed divergence times and paleoecological data suggest that continental species diverged in the late Pliocene or during the Pleistocene as a result of geographic isolation caused by climatic and vegetational change.
Peripherally isolated populations of common chaffinches (Fringilla coelebs) in the Canaries, Madeira, and Azores were compared genetically with their putative ancestral stock in Iberia and Morocco, and with a population of blue chaffinches (F. teydea) from Tenerife, using protein electrophoresis of 42 loci. The continental populations are only weakly differentiated genetically (FST = 0.092), despite distinctive subspecific differences in plumage and morphometrics between Iberia and Morocco populations. Estimated levels of gene flow among continental populations are high enough to account for their relative genetic homogeneity, and it is unlikely that homogenizing selection is operating to mimic the effects of gene flow. In contrast, the Atlantic island populations are well differentiated genetically (FST = 0.321), and have diverged considerably from their continental conspecifics. The development of significant genetic differentiation within the Canaries but not the Azores likely results from smaller population sizes, very restricted gene flow, and enhanced random drift in the former populations. There is no convincing evidence in support of stronger directional selection acting on genotypes or phenotypes to reduce within-population variability in Canaries populations as proposed by Grant (1979), although other tenets of his model of island evolution are supported by our analysis. Although genetic variability is reduced in four of the Canaries populations, only the Hierro population appears to have encountered a severe bottleneck. Yet it has not differentiated markedly from the La Palma population to which it is subspecifically allied. We conclude that gradual divergence in isolated populations of small to moderate size is the most plausible explanation for the evolution of intraspecific and interspecific diversity in Atlantic island chaffinches.
This study investigated allozyme and morphometric variability within the genus Cynopterus, with particular emphasis on C. nusatenggara, which is endemic to Wallacea, the area encompassing the Oriental-Australian biogeographic interface. The genetic distances between Cynopterus species are small by mammalian standards and suggest that this genus has undergone a recent series of speciation events. The genetic distance between populations of C. nusatenggara is strongly correlated with both the contemporary sea-crossing distance between islands and the estimated sea crossing at the time of the last Pleistocene glacial maximum, 18,000 b.p. This observation, together with low levels of population substructure within islands as shown by F-statistics, indicates that the sea is a primary and formidable barrier to gene exchange. The genetic distance and the great-circle geographical distance between the populations of C. nusatenggara are not correlated, although a principal-coordinates analysis of genetic distance reveals relationships between the populations that are similar to their geographical arrangement. A strong negative correlation exists between the level of heterozygosity within island populations of C. nusatenggara and the minimum sea-crossing distance to the nearest large source population. This is interpreted as reflecting an isolation effect of the sea, leading to reduced heterozygosity in populations that have larger sea barriers between them and the large source islands. Independently of this, heterozygosity is negatively associated with longitude, which in turn is associated with systematic changes in the environment such as a gradual decline in rainfall from west to east. The association between heterozygosity and longitude is interpreted as reflecting an association between genetic and environmental variance and supports the niche-width theory of genetic variance. Morphometric variability did not show any of the main effects demonstrated in the genetic data. Furthermore, there was no evidence that, at the level of individuals, genetic and morphometric variability were associated.
The Island Fox, Urocyon littoralis, is a dwarf form found on six of the Channel Islands located 30-98 km off the coast of southern California. The island populations differ in two variables that affect genetic variation: effective population size and duration of isolation. We estimate that the effective population size of foxes on the islands varies from approximately 150 to 1,000 individuals. Archeological and geological evidence suggests that foxes likely arrived on the three northern islands minimally 10,400-16,000 years ago and dispersed to the three southern islands 2,200-4,300 years ago. We use morphometrics, allozyme electrophoresis, mitochondrial DNA (mtDNA) restriction-site analysis, and analysis of hypervariable minisatellite DNA to measure variability within and distances among island fox populations. The amount of within-population variation is lowest for the smallest island populations and highest for the mainland population. However, the larger populations are sometimes less variable, with respect to some genetic measures, than expected. No distinct trends of variability with founding time are observed. Genetic distances among the island populations, as estimated by the four techniques, are not well correlated. The apparent lack of correspondence among techniques may reflect the effects of mutation rate and colonization history on the values of each genetic measure.
Mitochondrial DNA (mtDNA) from 131 deer mice, Peromyscus maniculatus, collected on the eight California Channel Islands and from seven southern California mainland locations, was isolated and analyzed for restriction endonuclease fragment polymorphisms. A total of 26 mtDNA genotypes were distinguishable among the deer mice sampled. All of the island samples had mtDNA restriction-fragment patterns not found among the mainland samples. Distributions of specific restriction-fragment patterns provide evidence for at least four separate colonization events to the Channel Islands. The estimated percentage of sequence divergence between all mtDNA's in this study was less than 1%, suggesting that colonization of the islands occurred fairly recently, probably within the last 500,000 years. Levels of mtDNA heterogeneity were much lower within island populations than within mainland populations.
The neutral theory claims that the great majority of evolutionary changes at the molecular level are controlled by random genetic drift under continued input of mutations, and that most of the genetic variation within species is maintained by the same mechanisms. The theory leads to a general view that since the origin of life on Earth, neutral evolutionary changes have played a most important role in evolution and predominated over Darwinian evolutionary changes, at least in number, throughout the whole history of life.
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.
. Genetic variability in individual troops of the Japanese macaque was quantified by two measures, that is, the proportion of polymorphic loci and the proportion of heterozygous loci per individual. The former averaged 10.8% and the latter 1.7%, and these values were remarkably lower than those estimated for other animal populations. Observations of the distribution patterns of genetic variations among the macaque troops indicated that an individual troop could not be regarded as a genetic isolate because of exchange of individuals with neighboring troops. Assuming the neutrality of segregating alleles and the two-dimensional stepping-stone model of population structure, the genetic migration rate between troops was estimated to average less than 5% per generation. Analyses of correlation between geographic and genetic distances between troops revealed that the gene constitutions of two troops apart more than 100 km could be regarded as practically independent of each other. These results suggest that the population structure of the Japanese macaque species has a tendency to split into a number of local subpopulations in which the effect of random genetic drift is prevailing.
Two steganacarid species, Steganacarus (Steganacarus) tenerifensis and S. (S.) carlosi, the first endemic to Tenerife and the second to La Gomera and Tenerife, were found to have such wide morphological variability as to east doubt on their specific limits. Cluster analysis and MDS ordering were used to quantify morphological variation, and biochemical procedures were used to assess genetic variation in the two entities. The results revealed disagreement between the morphological and genetic data as reported in previous studies on steganacarid mites. Morphological traits were highly heterogeneous in the Canary island populations and genetic structure was homogeneous with very low heterozygosity. The separation of the two Canary island species, not to mention the phenotypes close to carlosi, is difficult to justify due to their very high genetic identity. The presence of morphological intermediates suggests the same conclusion. However, the sympatry of some phenotypes and previous data on this animal group are a source of doubt and suggest that further investigations are needed before conclusions can be reached in this regard. Correlations between morphological differentiation and known palaeogeographic events are suggested in the light of the possible evolutionary history of the steganacarid mites on the Canary islands.
Scrutinizes historic extinctions in a detailed attempt to fathom their meaning in the context of Late Pleistocene losses. Historic disappearances of modern birds and mammals can be laid to a variety of effects, some climatic, some cultural. Also considers 'the extinctions which did not occur'. -after Editor
The evolutionary significance of genetic diversity of proteins in nature remains controversial despite the numerous protein studies conducted electrophoretically during the last two decades. Ironically, the discovery of extensive protein polymorphisms in nature (reviewed by Lewontin, 1974; Powell, 1975; Selander, 1976; Nevo 1978, 1983b; Hamrick et al., 1979; Nelson and Hedgecock, 1980), did not resolve the disagreement between the die ho torn ou s explanatory models of selection (e.g., Ayala, 1977; Milkman, 1978; Clarke, 1979; Wills, 1981) versus neutrality (Kimura, 1968; Kimura and Chta, 1971; Nei, 1975; and modifications in Kimura, 1979atb). The more general problem of the relative importance of the evolutionary forces interacting in genetic population differentiation at the molecular levels of proteins and DNA, i.e., mutation, migration, natural selection and genetic drift, remains now as enigmatic as ever.
Four subspecies of cotton mice (Peromyscus gossypinus) were examined to assess the taxonomic validity and affinities of the mice on Cumberland Island, Georgia, and Anastasia Island, Florida, both of which are presently referred to P. g. anastasae. Genetic analysis of 44 loci in 379 mice from 14 populations (six island, eight mainland) and morphometric analysis of 27 characters on 683 mice from 20 populations were performed. Polymorphic loci and heterozygosity per population averaged 40 and 10%, respectively, and there was no reduction of genetic variability on islands. Insular mice tended to be smaller than mainland mice. Every population was genetically or morphologically different from all other populations for at least one character in pairwise comparisons. However, when all populations were examined simultaneously, the pairwise differences were not significant. While each population was statistically distinct, none was unusually distinct, and neither the Cumberland Island nor Anastasia Island populations of P. g. anastasae warrant recognition as separate subspecies.
We have examined allozymic variation at 25 loci in nine species of Peromyscus inhabiting the southwestern United States, Sonora, Baja California, and islands in the Gulf of California. Four previously studied species of Peromyscus are also included in a dendrogram formed by cluster analysis of genic similarity coefficients. Mainland populations currently assigned to P. eremicus represent two distinctive genetic types, an eastern form in Nevada, New Mexico, Arizona, Texas, and Sonora, and a western form in southern California and Baja that may have been separated originally by the Gulf of California embayment in the Pleistocene. Peromyscus merriami is genically distinct from sympatric P. eremicus populations of the eastern type, although it falls within the range of genetic variation found between eastern and western P. eremicus forms. The insular endemics P. guardia, P. interparietalis, and P. dickeyi, and two insular subspecies of P. eremicus, are similar to the western P. eremicus type on Baja and probably share a recent common ancestor. Populations on shallow-water islands near Baja are more similar to mainland populations than are those on deep-water islands. Other insular species, P. caniceps and P. stephani, are genetically more distinct from P. eremicus and may have closer relationships with other mainland species. P. sejugis is closely related to P. polionotus (maniculatus species group) and probably evolved from maniculatus. There is considerable variation in level of genic heterozygosity among mainland populations, although the mean of six percent is consistent with "normal" heterozygosity estimates for other vertebrates. All insular populations have low variability, averaging less than one percent of loci in heterozygous state, presumably as a consequence of random drift in small populations.