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Mitochondrial DNA variation and evolutionary history of chromosome races of collared lemmings (Dicrostonyx) in the Eurasian Arctic
Abstract
Collared lemmings (Dicrostonyx) demonstrate extensive chromosome variation along their circumpolar distribution in the high Arctic. To reveal the history of this genus and the origin of chromosome races in the Palearctic, we studied the geographical pattern of mtDNA variation in lemmings from 13 localities by using eight tetranucleotide restriction enzymes. The main split in mtDNA phylogeny is at the Bering Strait and corresponds to the main chromosome division between the Beringian and the Eurasian groups of karyotypes. Nucleotide divergence estimate of 6.8% suggests that, despite the Bering Land Bridge, Palearctic and Nearctic forms have been separated since the mid-Pleistocene. Five distinct phylogenetic groups of mtDNA haplotypes, with average divergence of 1.5%, corresponding to geographical regions, were found along the Palearctic coast. Low nucleotide and haplotype diversity and a star-like phylogeny within phylogeographical groups of haplotypes suggest regional bottleneck events in the recent past, most probably due to warming events during the Holocene. There is congruence between phylogeographical pattern of mtDNA variation and geographical distribution of chromosome races; 69% of the total mtDNA variation is allocated among chromosome races. This congruence implies that historical events such as fragmentation and allopatric bottleneck events have been important for the origin of chromosome races. However, historical factors do not explain the fixed autosome fusions found to distinguish certain populations.
... This second hypothesis postulates multiple refugia, such as those identified in Europe or Beringia, contributing to the recolonization of Eurasia. This model has primarily been described for tundra and grassland species (Fedorov et al., 1999a;Brunhoff et al., 2003;Hope et al., 2011). A few putative Asian refugia also have been inferred based on fossils, palaeoecological reconstructions, and comparative molecular studies, most notably in the Ural Mountains and northern Mongolia (Markova et al., 1995;Tarasov et al., 2000;Todisco et al., 2012), and south-east Siberia and the Amga River basin (Fedorov et al., 2008;Hope et al., 2011). ...
... H 1b -Populations of M. rutilus were isolated in multiple Eurasian refugia and subsequently expanded to their present continuous Palaearctic distribution. Initial divergence may correspond to the LGM or an earlier glacial period, as seen in other northern mammals (Fedorov et al., 1999a;Brunhoff et al., 2003;Hope et al., 2011). Predictions associated with this multiple Eurasian refugia (MER) hypothesis and isolation over long periods include the presence of two or more lineages in Eurasia that may have diverged and expanded before the LGM, contact zones between divergent phylogroups and relatively high genetic diversity across the continent. ...
... Such a history is distinct from most Eurasian boreal species that each apparently dispersed to their current wide Palaearctic distributions from a single refugial source (see Fedorov et al., 2008;Korsten et al., 2009; and references therein). Greater genetic divergence and structure in M. rutilus is more similar to tundra or grassland species whose modern phylogeographical structure reflects greater influence from vicariance than dispersal (Fedorov et al., 1999a;Brunhoff et al., 2003). These results suggest that pre-LGM vicariance events generated Holarctic structure in northern red-backed voles and underscore the idiosyncratic response of species to major environmental perturbations (Stewart, 2009;Hope et al., 2011). ...
AimWe used the Holarctic northern red-backed vole (Myodes rutilus) as a model organism to improve our understanding of how dynamic, northern high-latitude environments have affected the genetic diversity, demography and distribution of boreal organisms. We tested spatial and temporal hypotheses derived from previous mitochondrial studies, comparative phylogeography, palaeoecology and the fossil record regarding diversification of M. rutilus in the Palaearctic and Beringia.LocationHigh-latitude biomes across the Holarctic.Methods
We used a multilocus phylogeographical approach combined with species distribution models to characterize the biogeographical and demographic history of M. rutilus. Our molecular assessment included widespread sampling (more than 100 localities), species tree reconstruction and population genetic analyses.ResultsThree well-differentiated mitochondrial lineages correspond to geographical regions, but nuclear genes were less structured. Multilocus divergence estimates indicated that diversification of M. rutilus was driven by events occurring before c. 100 ka. Population expansion in all three clades occurred prior to the Last Glacial Maximum (LGM) and presumably led to secondary contact. Species distribution modelling predicted a broad LGM distribution consistent with population and range expansion during this period.Main conclusionsThe biogeographical history of M. rutilus differs from other boreal forest-associated species. Well-differentiated clades and the existence of secondary contact zones indicate prolonged isolation and persistence in Eurasian and Beringian refugia. Dynamic demographic and distributional changes emphasize the impact of pre-LGM glacial–interglacial cycles on contemporary geographical structure. The Bering Strait was not a significant factor in the diversification of northern red-backed voles.
... The best-studied examples of the phylogeography of arctic terrestrial mammals are those of Fedorov (1999) and Fedorov et al. (1999aFedorov et al. ( , 1999b, who examined the distributions of mtDNA haplotypes in true lemmings, Lemmus (Fedorov 1999, Fedorov et al. 1999a) and the collared lemming, Dicrostonyx (Fedorov 1999, Fedorov et al. 1999b, Fedorov & Goropashnaya 1999. Fedorov et al. (1999a) screened populations of Lemmus sp. from across northern Eurasia for variation in mtDNA RFLPs and mtDNA cytochrome b sequence variation and uncovered the presence of three distinct lineages (west, central, east). ...
... The best-studied examples of the phylogeography of arctic terrestrial mammals are those of Fedorov (1999) and Fedorov et al. (1999aFedorov et al. ( , 1999b, who examined the distributions of mtDNA haplotypes in true lemmings, Lemmus (Fedorov 1999, Fedorov et al. 1999a) and the collared lemming, Dicrostonyx (Fedorov 1999, Fedorov et al. 1999b, Fedorov & Goropashnaya 1999. Fedorov et al. (1999a) screened populations of Lemmus sp. from across northern Eurasia for variation in mtDNA RFLPs and mtDNA cytochrome b sequence variation and uncovered the presence of three distinct lineages (west, central, east). ...
... Phylogeography of the collared lemming, Dicrostonyx (Fedorov et al. 1999b, Fedorov & Goropashnaya 1999 was also examined using mtDNA RFLPs, DNA sequencing, and karyotyping of different chromosomal races across its arctic range. Fedorov et al. (1999b) found the main split in mtDNA phylogeny at the Bering Strait, which also corresponds with the main chromosomal division between the Beringian and the Eurasian karyotype groups. ...
Current concerns over the impact that anthropogenic global climate change will have on levels of biodiversity have focused mainly on tropical and temperate systems. Recently, attention has turned to polar systems and the potential impacts these climatic changes might have on polar flora and fauna. Polar organisms have been subjected to dramatic fluctuations in environmental conditions during the Holocene and Pleistocene, so one might expect these systems to be resilient. However, little is really known of how such global climate changes will impact biodiversity in the arctic. What is known, particularly through the use of molecular markers, is that glacial cycles have impacted the evolutionary trajectories of many extant polar species. By studying these organisms, particularly those found across the Holarctic, one can examine the dynamic interaction between deterministic forces (e.g. selection) and historical processes (e.g., vicariance event) in order to better understand how these processes have impacted the phylogeography and genetic divergence among taxa. Keeping with the "northern dimensions" theme of this symposium, we review results obtained from a variety of phylogeographic studies that have examined the importance of dispersal, vicariance and selection in shaping the distributions of arctic biota, especially among closely-related species complexes. In particular, We examine the recent debate over the importance of Pleistocene glacial cycles in influencing population genetic differentiation and speciation. Finally, we provide an assessment of how studying these arctic systems will benefit the global perspective on climate change research.
... Because biotic complexity at high latitudes is decreased compared with lower latitudes, the Arctic could be a particularly suitable region for tracking responses to environmental changes and teasing apart the effects of abiotic events on the structure of extant diversity (Weider and Hobaek 2000). Phylogeographic analyses, which explore the relationship between gene genealogies and geography, are beginning to identify genetic structure within this vast region (Brunhoff et al. 2003;Fedorov and Goropashnaya 1999;Fedorov et al. 1999aFedorov et al. , 1999bGalbreath and Cook 2004;Holder et al. 2000;Wenink et al. 1996). ...
... More recently, phylogeographic discontinuities in plants and mammals have been described at the Parry Channel and Mackenzie River in northern Canada (Abbott et al. 2000;Ehrich et al. 2000;Fedorov and Stenseth 2002;Fedorov et al. 2003;MacPherson 1965;Tremblay and Schoen 1999). In addition, the Kolyma and Omolon river systems in Far East Russia have been shown to separate lineages in birds and small mammals (Brunhoff et al. 2003;Fedorov et al. 1999aFedorov et al. , 1999bFedorov et al. , 2003Galbreath and Cook 2004;Wenink et al. 1996). The generality of these discontinuities can be further tested by studying the comparative biogeography of additional taxa with similar Holarctic distributions. ...
... However, there is a complicated relationship between maximum likelihood bootstrap values and Bayesian branch support Whittingham et al. 2002), and some of the 6 described clades have low maximum likelihood bootstrap support. Within the arctic hares, all L. arcticus haplotypes form a moderately supported ( Brunhoff et al. 2003;Fedorov and Stenseth 2002;Fedorov et al. 1999a;Galbreath and Cook 2004). In addition, L. coreanus appears nested within the arctic hares (Fig. 4). ...
Phylogeographic analyses of arctic organisms provide spatial and temporal frameworks for interpreting the role of climate change on biotic diversity in high-latitude ecosystems. Phylogenetic analyses based on 673 base pairs of the mitochondrial control region from 95 arctic hares (Lepus arcticus, L. othus, L. timidus) and 2 other Lepus species identified 6 strongly or moderately supported clades. The 3 arctic hare species are closely related, but phylogenetic discontinuities were found at the eastern and western boundaries of Beringia, the latter not previously identified as a species boundary. The locations of these discontinuities are congruent with previously described genetic breaks in Arctic plants, birds, and small mammals. Similarly, the finding of a Beringian clade corroborates previous studies identifying Beringia as a refugium. A coalescent view of a population on Seward Peninsula, Alaska (eastern Beringia), did not, however, provide a genetic signature of population expansion. In contrast, a Greenland population did show a signal of expansion.
... The fossil record shows that during glacial periods, collared lemmings expanded their distribution thousands of kilometers to the south and west while in warm periods of the past and present interglacials their range was restricted to the Arctic (11). Previous studies have revealed the low mitochondrial (mt)DNA diversity in the Eurasian collared lemmings, suggesting reductions in long-term effective population size which most likely resulted from range contractions during the Late Quaternary warming events (12,13). However, this explanation remains ambiguous due to the obscure position of the root in phylogeny, uncertain calibration of the molecular clock, and limited sampling in the extreme northeast of the Eurasian Arctic. ...
... This difference in demographic history cannot be directly attributed to the impact of the last glaciation, as most of the Eurasian Arctic was not glaciated (34). It was suggested that the low mtDNA diversity resulted from regional bottleneck events due to the northward forest expansion contracting suitable tundra habitats to the west of the Kolyma River during Holocene warming (12,13). Pollen and plant macrofossil records show that, over a large part of northern Eurasia, forest expanded to or near the Arctic coastline between 10 and 3 kyr during the Holocene thermal maximum (35)(36)(37)(38). ...
Arctic climate was warmer than today at the last interglacial and the Holocene thermal optimum. To reveal the impact of past climate warming events on the demographic history of an Arctic specialist, we examined both mitochondrial and nuclear genomic variation in the collared lemming (Dicrostonyx torquatus, Pallas), a keystone species in tundra communities, across its entire distribution in northern Eurasia. The ancestral phylogenetic position of the West Beringian group and divergence time estimates support the hypothesis of continental range contraction to a single refugial area located in West Beringia during high magnitude warming of the last interglacial, followed by westward recolonization of northern Eurasia in the last glacial period. The West Beringian group harbors the highest mitogenome diversity and its inferred demography indicates a constantly large effective population size over the late Pleistocene - Holocene. This suggests that northward forest expansion during recent warming of the Holocene thermal optimum did not affect the gene pool of the collared lemming in West Beringia but reduced genomic diversity and effective population size in all other regions of the Eurasian Arctic. Demographic inference from genomic diversity was corroborated by species distribution modeling showing reduction in species distribution during the past climate warming. These conclusions are supported by recent paleoecological evidence suggesting smaller temperature increase and moderate northward forest advances in the extreme northeast of Eurasia during the late Pleistocene - Holocene warming events. This study emphasizes the importance of West Beringia as a potential refugium for cold-adapted Arctic species under ongoing climate warming.
... Currently, eight valid species are recognized in the genus Dicrostonyx based on morphological, caryological, hybridological and genetic data (Rausch & Rausch 1972;Tchernyavskiy & Kozlovskiy 1980;Krohne 1982;Gileva 1983;van Wynsberghe & Engstrom 1992;Borowik & Engstrom 1993;Engstrom et al. 1993;Eger 1995;Fedorov et al. 1999;Ehrich et al. 2000;Abramson & Tikhonova 2002;Musser & Carleton 2005). Only two species inhabit Eurasia: D. torquatus (Pallas, 1779) on the continent and D. vinogradovi (Ognev, 1948) on Wrangel Island; the six other species live in North America. ...
... According to the results of Recent and ancient mtDNA investigations (Fedorov et al. 1999;Prost et al. 2010;Brace et al. 2012), there is one mtDNA haplotype subclade in the western part of the Recent and Holocene Dicrostonyx range. This clade is part of the haplotype clade lineage 5 defined in a previous study (Brace et al. 2012); this clade was widespread at least in western and NE Europe after the LGM time (20-14 ka BP) (Brace et al. 2012). ...
An approach combining traditional morphotypical methods, multivariate analysis and informational-statistical methods was used to study evolutionary changes in the occlusal shape of the first and second upper molars of Recent and Middle–Late Pleistocene Dicrostonyx (32 samples) from localities in northeast European Russia (northeastern Russian Plain, the Timan Ridge and the northern part of the Urals). The evolutionary history is described in terms of morphological evolutionary levels of teeth suggested by Smirnov et al. (1997, Materialy Po Istorii I Sovremennomu Sostojaniju Fauny Severa Zapadnoj Sibiri: Sbornik Nauchnyh Trudov, Chelyabinsk, slightly modified). Based on 14C-dated samples, levels of molar evolution did not always successively replace each other in time, but rather there were often synchronous populations at any given level. This finding supports the notion of a mosaic pattern of morphotypical diversity and relatively independent, parallel evolution of lemming teeth amongst different populations. Six relatively distinct stages in the evolutionary history of Dicrostonyx from the Pechora (Dnieper) to Recent time have been described, but estimations of their relative ages are often debatable. The rates of change in the M1 and M2 morphotypes and morphological diversity in collared lemmings varied over the entire time interval. The fastest replacement of morphotypes and the highest level of morphological diversity in the study area occurred approximately during the Lateglacial (16–10 cal. ka BP). In the present study, we suggest a new version of evolutionary history of collared lemmings in northeast European Russia, taking into consideration the morphological variability of molars, radiocarbon dates and geological data. Our results provide a more detailed pattern of species evolution in the studied region and specific ages of some localities.
... For example , birds (e.g. dunlin Caladris alpina) and rodents (Lemmus , Dicrostonyx, Microtus oeconomus) share suture zones where distinct evolutionary groups come together, and these correlate to the western (Kolyma Mountain uplands ) and the eastern (Mackenzie River/eastern Alaska Range) borders of Beringia (Hewitt 1996, Wenink et al. 1996, Fedorov et al. 1999b, 2003, Fedorov & Stenseth 2002, Brunhoff et al. 2003, Galbreath & Cook 2004). Genetic studies of Arctic species showing overall high levels of genetic diversity have verified the role of Beringia as a major refugium (Hultén 1937, Abbott & Brochmann 2003). ...
... The influence of the Bering Strait often is not reflected in genetic analyses of terrestrial organisms suggesting that this oceanic divide between Asia and North America (most recently formed 11,000 years ago) has minimally influenced divergence within Holarctic mammals (Brunhoff et al. 2003, Galbreath & Cook 2004) and some birds, including migratory species (Pearce et al. 2004). In a number of avian species (Zink et al. 1995, Wenink et al. 1996) and terrestrial mammals that are ecologically associated with dry environments, however, this barrier delineates significant genetic breaks (Fedorov & Goropashnaya 1999, Fedorov et al. 1999b, Wickström et al. 2003). Some species that share habitats and distributions show idiosyncratic histories with regard to expansion out of high latitude refugia, and thus are sensitive to different barriers (Box 17.6). ...
The impact of climate warming on Arctic organisms is complex, and its interpretation will require a concerted effort. To mitigate the impact of climate-induced perturbations, an essential first step is to develop an understanding of how high latitude species and ecosystems were influenced by past episodes of dynamic environmental change. One of our best views of past change in Arctic populations is through molecular genetics (e.g. DNA studies). DNA-based views provide a basis for forecasting how biomes and individual species will respond in the future and thus are a key component of an advanced early-warning system for natural environments of the Arctic.
Species typically adapt to new conditions or shift into new areas, but a number of Arctic species are now experiencing a reduction in their distributions, abundance and ability to exchange individuals among populations. Molecular genetic approaches are used in a wide range of studies to provide comprehensive assessments of how species interact with their environments. Important insights have been gained related to the conservation status of high latitude species of concern, but because Arctic environments are remote and difficult to access, only limited information is available about most essential factors for organisms (e.g. contemporary genetic diversity, evolutionary history, modes of reproduction). A oordinated
investment in biological infrastructure is needed now (similar to that already in place for monitoring the physical environment) if we are to apply and realize the powerful insights provided by molecular genetics.
... The ge netic dis con ti nuities in re cent taxa of the north ern high lat itudes are a re sult of the bi otic in ter change be tween con ti nents dur ing the gla cial max ima, recolonizations in re sponse to cli mate change, and ef fects of a large-scale hab i tat frag men tation on ge netic di ver sity and, ul ti mately, on speciation (Waltari et al. 2004). So far, the follow ing geographic bar ri ers in duc ing the ge netic dis con ti nu ities of many plant and an i mal species have been rec og nized: the Be ring Strait, Parry Chan nel and Mac ken zie River in north ern Can ada (Abbott et al. 2000, Ehrich et al. 2000, Fedorov and Stenseth 2002, Waltari et al. 2004, and the Kolyma and Omolon river sys tems in Far East Rus sia (Wenink et al. 1996, Fedorov et al. 1999a, Galbreath and Cook 2004, Waltari et al. 2004. ...
... The fact that the area had never been sub jected to the glaciations (Hopkins 1967, Frenzel 1968), however, meant that the re gion pro vided im por tant ref uges for many taxa dur ing the Pleis to cene glaci ation. In the case of small mam mals, such as Microtus oeconomus, Dicrostonyx groenlandicus and ge nus Lepus, it was ob served that the pop ula tions from the Beringian re gion (ie eastwards from the Omolon River and west of the Mac kenzie River) form a phylogeographically sep a rate clade -Beringian clade (Fedorov 1999a, Brunhoff et al. 2003, Waltari et al. 2004. Also the red fox pop u la tions from the Beringian re gion form a sep a rate clus ter. ...
Research into the geographical pattern of tooth size in the red fox,Vulpes vulpes (Linnaeus, 1758) in the Holarctic was conducted on a sample of 3806 skulls belonging to 41 fox populations. The Nearctic
was represented by 948 specimens (249 females, 359 males, 340 specimens of unknown sex) belonging to 13 populations, whereas
the Palearctic was represented by 2858 red foxes (1034 females, 1256 males, 568 specimens of unknown sex) from 32 populations.
In the Nearctic, the largest foxes live on Kodiak Island (V. v. harrimani) and the Kenai Peninsula (V. v. kenaiensis), while the smallest ones live in California (V. v. necator) and Georgia (V. v. fulvus). In the Palearctic, the largest foxes come from the Far East (V. v. jakutensis, V. v. beringiana, V. v. tobolica), while the smallest are from the southern borders of the Eurasian range (V. v. pusilla, V. v. barbara, V. v. arabica). In both the Palearctic and Nearctic, tooth size in the fox varies depending on the geo-climatic factors. The fox’s tooth
size confirms the general basis of Bergmann’s rule. In the Palearctic, specimens with larger teeth occur in cooler habitats
with greater seasonality. These are first and foremost Northern and Far Eastern populations. In the Nearctic, tooth size in
red foxes depends on the temperature and humidity of their habitat. Competition within the species and between species has
important impact on the variation and dimorphism of tooth size in the red fox. Both in the Nearctic and Palearctic, red foxes
from regions of sympatric co-occurrence with other closely relatedVulpes species, are more sexually dimorphic in terms of tooth size than red foxes from allopatric regions. Analysis of morphological
distance on the basis of the size of dental characteristics shows, that in the Palearctic, the foxes from India (V. v. pusilla), while in the Nearctic, the population from Kodiak Island (V. v. harrimani) are most distant from the remaining populations. Geographic barriers such as the Bering Strait, Parry Channel, Mackenzie
River, Kolyma and Omolon River systems have had a critical impact on red fox evolution. The most likely place for the evolution
and diversification of the phyletic lineVulpes vulpes seems to be the Middle East region.
... We present original data concerning the geographical distribution of haplotypes of the mtDNA control region in the three Rb races and in the surrounding standard populations in order to test the different hypotheses of raciation. Congruence between the geographical pattern of mtDNA and chromosomal variation should indicate that the origin of Rb races is mainly determined by allopatric events giving evidence for a history of isolation (Fedorov, Fredga & Jarrell, 1999). In contrast, a lack of congruence and a star-like phylogeny of mtDNA sequences should indicate a mode of raciation not involving geographical isolation (a stasipatric-like mode of chromosomal evolution) (Ratkiewicz et al ., 2002). ...
... In S. araneus, a star-like phylogeny of haplotypes and a pattern of mtDNA variation unrelated to the races fits a stasipatric mode of chromosomal evolution better than an allopatric mode (Ratkiewicz et al., 2002). In contrast, Fedorov et al. (1999) analysed the origin of the chromosomal races of the collared lemming Dicrostonyx sp. The genetic structure indicated that bottlenecks and allopatric events most likely caused chromosomal diversification in this species. ...
The Robertsonian (Rb) system of Mus musculus domesticus in central Italy consists of three Rb races (CD, 2n = 22; CB, 2n = 22; ACR, 2n = 24), and additional Rb populations with new metacentrics have recently been reported. The aim of the present paper is to provide insight into the process of house mouse raciation in this area. Here we present new data concerning the geographical distribution of mtDNA haplotypes (control region sequence) in the three Rb races and in the surrounding standard populations. The presence of exclusive clades in all the three Rb races supports the idea of a past fragmentation event and a subsequent period of isolation. However, comparison of mtDNA polymorphism between Rb and standard races, and the shape of the mismatch distribution within the races, does not reveal any clear sign of a strong reduction in population size, at this geographical scale, related to race formation. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 84, 395–405.
... Recent phylogeographical studies suggest a general pattern of genetic variation in species distributed across Eurasia in addition to that exhibited by small mammals (Fedorov, Fredga & Jarrell, 1999a;Jaarola & Searle, 2002). A number of species have low levels of genetic variation, which are observed as shallow phylogenetic trees or star-like networks (Hundertmark et al., 2002;Babik et al., 2004;Ritzerow, Konrad & Stauffer, 2004), and could be attributed to fast range expansion over a very large geographical area. ...
... There is often only limited congruence between haplotype and geographical distributions (Fedorov et al., 1999b;Kvist et al., 2001;Zink, Drovetski & Rohwer, 2002;Flagstad & Røed, 2003;Kvist et al., 2003;Goropashnaya et al., 2004), and no clear indication of refugial areas or recolonization routes. In addition, there are clear phylogeographical splits (Zink et al., 2002;Fedorov et al., 1999a;Franzke et al., 2004;Goropashnaya et al., 2004), or indications of population expansion (Flagstad & Røed, 2003) that predate the Weichselian. Although glaciation was mimimal in eastern Eurasia, this area was extremely cold and arid during glacial periods (Anderson & Borns, 1997) and covered by large expanses of tundra and steppe vegetation (Grichuk, 1984;Tarasov et al., 2000). ...
Many species that occur in formerly glaciated areas of Fennoscandia have reached their current ranges from glacial refugial areas in Eurasia. Little is known of the refugia and postglacial colonization routes of insect species that are confined to boreal forests. Here, we investigate the phylogeography of three species of saproxylic beetles distributed across Eurasia: two rare boreal forest specialists, Pytho kolwensis and Pytho abieticola, and a common, less specialized species, Pytho depressus. In all species, there were two well-defined haplotype clades based on 645 bp of cytochrome oxidase subunit I gene sequence. In each species one clade was found only in China. The other clade occurred from China to north-western Europe in both P. kolwensis and P. depressus, but was apparently absent from China in P. abieticola. In spite of common phylogeographical patterns, the distribution of genetic variation differed markedly between the three species. In P. kolwensis, a highly-threatened species in old-growth forests in Fennoscandia, there was an extremely low level of genetic variation throughout Eurasia. One common haplotype, represented by 86% of the samples, dominated in all sampling localities. Levels of genetic variation were higher in both P. abieticola and P. depressus, with 31% and 58%, respectively, of the samples representing a unique haplotype. In each species, relationships between haplotypes were not well resolved, and haplotypes from one sampling locality were generally not clustered in either Neighbour-joining trees or statistical parsimony networks. These patterns in the distribution of genetic variation can be attributed to differences in the species’ population sizes, ecologies, glacial refugial areas, and postglacial colonization dynamics. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 91, 267–279.
... En general estas especies presentan una reducción direccional de sus variación genética asía latitudes altas con linajes genéticos de reciente o nula divergencia (Stewart et al. 2010). Las penínsulas del sur de Europa, Italia, Ibérica y Balcanes actuaron como refugio para muchas especies lo cual da como resultado altos niveles de diversidad taxonómica y genética en estas regiones (Hewitt 2004 pasado, donde la población se redujo durante el actual periodo interglaciar (Fedorov et al. 1999;Flagstad & Røed 2003;Shapiro et al. 2004), mientras los pocos estudios filogeográficos de especies distribuidas en los bosques templados de los Trópicos y Subtròpicos revelan una gran diversidad genética con linajes de reciente y antigua divergencia, donde se sugiere persistencia de las especies incluso desde el Plioceno (Hace 5.3 millones de años) que podría indicar que en algunos casos los cambios climáticos del cuaternario no parecen tener influencia significativa sobre el patrón filogeográfico (Hewitt 2004). ...
El estudio filogeográfico ha documentado que los eventos geológicos del Plioceno junto a los ciclos glaciares del Cuaternario, tuvieron un papel muy importante en la diversificación biológica de Norteamérica. La especie Myioborus miniatus habita desde el norte de México hasta Argentina, tiene un registro de 12 subespecies a partir de diferencias morfológicas.
Un estudio filogeográfico relacionó la variación genética subespecífica con la discontinuidad del hábitat y cambios climáticos durante el Pleistoceno Tardío. Sin embargo, no se integró a la subespecie Myioborus miniatus miniatus. Este trabajo se plantea como propósito deducir el patrón filogeográfico de la subespecie Myioborus miniatus miniatus.
A partir de la obtención de 62 secuencias del gen mitocondrial ND2, se realizó un árbol filogenético bayesiano, una red de haplotipos y se obtuvieron los índices de diversidad genética y valores de FST entre las poblaciones. La historia demográfica fue descrita con
los índices D de Tajima, F de Fu y valor de regardness, el valor de Tau permitió calcular el tiempo desde que comenzó la expansión. Por último, el tamaño efectivo de la población a través del tiempo fue graficado por medio de un análisis bayesiano Skyline Plot.
El análisis filogenético, que incluye todas las subespecies de Myioborus miniatus, indico que M. miniatus miniatus se encuentra en el linaje basal, además, este presenta un nodo bien soportado pero sin monófilia. . La diversidad genética presento un valor alto (0.8909) mientras que la diversidad nucleotidica promedio fue de 0.00191. El análisis de genética de poblaciones indica que no hay estructura genética. En cuanto a la historia demográfica,
el análisis Skyline Plot y pruebas de neutralidad indican un escenario de expansión demográfica. A su vez las pruebas de distribución mismatch indican un cambio súbito en el tamaño de la población. En conjunto los resultados indican un incremento del tamaño efectivo de la población durante el último máximo glaciar hace 60 mil años.
... Strong correspondence between evolutionary relationships and geographic distribution of genes (i.e., phylogeographic structure) has been found in the Arctic that reflects substantial endemism in many terrestrial free living and parasitic animals that have been sampled at continental and circumpolar scales [8][9][10][11][12]. The geographic locations of major evolutionary splits are largely similar across different species and coincide around mountain ranges that were formerly glaciated such as the Ural, Verhoyanskiy, Anuiskiy, and Richardson Mountains. ...
... Collared lemmings have a nearly circumpolar distribution (Federov et al, 1999), and genetic analyses suggest that they disperse long distances over sea ice (Ehrlich et al, 2001). This species is well known for its population cycles (Ehrlich et al, 2001;Wilson and Bromley, 2001), although Krebs et al (1995) and Predavec et al (2001) provide evidence of non-cyclic populations. ...
This document has been prepared in support of the proposal of Cumberland Resources Ltd. (Cumberland) to develop the Meadowbank Gold property, located approximately 75 km north of Baker Lake, Kivalliq Region, Nunavut. The objective of this report is to provide baseline information on soils and terrain, vegetation, and terrestrial wildlife in and around the Meadowbank Gold property.
Two study areas, a Regional Study Area (RSA) and a Local Study Area (LSA) were originally established for the purposes of conducting baseline surveys of the proposed project area. The RSA was 100 x 100 km (10,000 km2), and was centered on the field camp (the site of the future plant site). The LSA was 91 km2, and included two sites: a 5 km radius area centered on the field camp and a 2 km radius area centered on the Vault gold deposit, located adjacent to the northeast border of the first site. A third study area included a 5 km wide survey corridor centered on the proposed winter road between the Meadowbank Camp and Baker Lake. The majority (62%) of the winter road corridor was within the RSA.
In 2005, the study area boundaries of the RSA and LSA were revised to make them more suitable for long-term monitoring purposes. The RSA was reduced to include a 25 km radius circle around the main site and a 50 km wide corridor along the proposed all-weather access road route from the Meadowbank camp to Baker Lake (total area of 5,108 km2). The mine LSA was expanded to include both a 5 km radius area centred on the main site and a 5 km radius area around the Vault site creating an elliptical shape (total area of 194 km2). The access road LSA includes a 3 km wide corridor centred on the proposed all-weather access road between Baker Lake and the proposed mine site (total area of 276 km2).
Baseline surveys were conducted for the terrestrial components described in this report as follows:
Vegetation
– LSA surveys in August 1999, 2002 and 2005
– phenology studies in summer 2003 to 2005.
Wildlife
– aerial LSA surveys: one in 2002, three in 2003, four in 2004, and two in 2005, for a total of 10 surveys to date
– ground LSA surveys: one in 1999, two in 2002, six in 2003, eleven in 2004, and five in 2005, for a total of 25 surveys to date
– aerial RSA surveys: one in 1999, two in 2002, one in 2003, four in 2004, and three in 2005 for a total of 11 surveys (another survey is planned for October 2005)
– aerial survey of the winter road corridor: one in 2003 and three in 2004, for a total of four surveys
– winter ground surveys of the winter road corridor: four in 2003 and eighteen in 2004, for a total of 22 surveys
– winter ground surveys of the proposed all-weather access road: sixteen in 2005
– breeding bird surveys (PRISM method) in the mine site LSA: 26 plots in 2003 and 23 in 2004, and in the mine site LSA (19 plots, randomly selected subset of the previous 49 plots), and a control area (20 plots) in 2005
– waterfowl nesting surveys in close proximity to proposed mine facilities in 2004 and 2005
– breeding bird transects (12 transects, 3 km long) along the all-weather access road
– checklist bird surveys between 2003 and 2005
– incidental observations recorded in the Meadowbank camp wildlife log from 1996 to 1999 and 2002 to 2005.
Descriptions of baseline terrain and soils conditions in the LSA and RSA were obtained from a literature review, and from results of vegetation baseline surveys and surficial materials studies that were conducted in the LSA. The most common vegetated Ecological Land Classification (ELC) unit in the mine site LSA was the Sedge community association (20%). Water was another very common ELC unit in the area (31%). In the access road LSA, Heath Tundra was by far the most common unit (29%), followed by Lichen, and Birch and Riparian Shrub. In the overall RSA, Heath Tundra made up 23%, followed by water (19%), Lichen (14%), and Birch & Riparian Shrub (13%).
During the baseline wildlife surveys, 61 terrestrial wildlife species (12 mammals, 49 birds) were recorded in the Meadowbank area. Barren-ground caribou (Rangifer tarandus ssp. groenlandicus) was the most common mammal species recorded. Caribou are present in considerable numbers during the fall, winter, and spring, but are very sparsely distributed in summer, indicating that the RSA was not used as a major calving ground. Based on traditional and scientific knowledge of the area, caribou wintering in the RSA appear to originate from a number of different herds in the region. Other common mammal species recorded in the Meadowbank area included muskox (Ovibos moschatus), Arctic hare (Lepus arcticus), Arctic ground squirrel (Spermophilus parryi) and Arctic fox (Alopex lagopus).
Bird species observed in greater numbers than any other species during the surveys were snow goose (Chen caerulescens), Canada goose (Branta canadensis), Lapland longspur (Calcarius lapponicus), and horned lark (Eremophila alpestris). Other commonly observed breeding bird species were savannah sparrow (Passerculus sandwichensis), semipalmated sandpiper (Calidris pusilla), sandhill crane (Grus canadensis), and rock ptarmigan (Lagopus mutus). Sandhill crane, Canada goose, and snow goose were most common during the migratory period. Raptors, as well as all three species of jaegers, were recorded occasionally during baseline surveys.
A literature review was conducted for each of 29 wildlife species selected based on their abundance, conservation concern in the Meadowbank area, and interest to Baker Lake residents:
• Ungulates: barren-ground caribou, muskox
• Carnivores: grizzly bear (Ursus arctos), wolf (Canis lupus), wolverine (Gulo gulo)
• Furbearers: Arctic fox, ermine (Mustela erminea)
• Small mammals: Arctic hare, Arctic ground squirrel, collared lemming (Dicrostonyx groenlandicus), northern red-backed vole (Clethrionomys rutilis)
• Waterfowl: greater white-fronted goose (Anser albifrons), snow goose, Ross’ goose (Chen rossii), Canada goose, long-tailed duck (Clangula hyemalis)
• Raptors: rough-legged hawk (Buteo lagopus), gyrfalcon (Falco rusticolus), snowy owl (Nyctea scandiaca), peregrine falcon (Falco peregrinus tundrius)
• Ptarmigan: rock ptarmigan, willow ptarmigan (Lagopus lagopus)
• Shorebirds: semipalmated sandpiper, American golden-plover (Pluvialis dominica)
• Passerines: horned lark, American pipit (Anthus rubescens), white-crowned sparrow (Zonotrichia leucophrys), Lapland longspur, snow bunting (Plectrophenax nivalis).
... According to the second hypothesis (sympatric chromosome speciation stasipatric model of White 1968White , 1978 the pattern of geographic distribution of cromosomal races and mtDNA clades may be different. Two independent studies carried on Dicrostonyx (Engstrom et al., 1993;Fedorov et al., 1999) showed that there are no any substantial correspondence between chromosome races and mtDNA clades, and the second model of chromosome race origin is more appropriate. Our data on cranial and mandibular morphology also favor the second hypothesis. ...
... Slanted lines indicate extent of major ice sheets at the LGM. Bayesian cytochrome-b phylogeny reconstruction (Alaska: [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]Siberia: 29,[30][31][32][33][34][35][36]39,44,47,50,51,54,[56][57][58]SE Siberia: 41,42,48,52,59;MNA: 37,45,60,61;28,38,40,43,49,53,55;26,27) Posterior probabilities for major nodes are illustrated. Sorex hosonoi, a Honshu Island endemic, is included as the sister species. ...
... Several studies have dealt with the phylogeography of widespread northern Palearctic animals, including mammals such as badger Meles meles [16], hares Lepus spp. [17], and various rodents [18][19][20][21][22][23], as well as birds including ducks [24], shorebirds [25,26], woodpeckers [27,28], and several species of passerines [26,[29][30][31][32][33][34][35][36][37][38][39][40][41]. ...
... However, the time of origin and ancestral distribution of these animals, and the historical events that might have impacted their evolutionary dynamics, are less discussed. The refugia theory proposed by Haffer (1969) has been extensively used in interpreting the history of various organisms, especially the terrestrial rodents (Fedorov et al. 1999;Jaarola and Searle 2002;Haynes et al. 2003). But as for the arboreal populations or the flying squirrels, very few paleobiological studies [e.g. ...
Flying squirrels are strictly arboreal squirrels adopting a special gliding form of locomotion. This group of animals has a long history that has mirrored the vicissitude of forests. The discrepancy in the distribution between fossils and extant species indicates a mysterious evolution history requiring further exploration. This study compiles the worldwide fossils of Pteromyini to the species level in order to reproduce the spatiotemporal distribution pattern of flying squirrels and deduce the ancestral distribution according to dispersal-vicariance analysis of a phylogeny of the extant species. In addition, we reconstruct the paleoenvironmental background and find that flying squirrels probably originated in the Oligocene–Miocene transition from Europe and immediately dispersed to Asia and North America. Influenced by glaciation, CO2 reduction, geologic movements and the Paratethys retreat, the Northern Hemisphere underwent climate deterioration and grassland expansion during the late Miocene, and thus the diversity of Pteromyini dramatically decreased. The uplift of the Tibet Plateau in addition to the strengthened Asian monsoons intensified the aridity in central Asia, but brought sufficient water to the densely forested regions of South and Southeast Asia. These forests are likely both refugia and diversification center for flying squirrels during glacial periods in the Quarternary. The subsequent connection and separation events among these heterogeneous habitats has probably been a driving force in the speciation of flying squirrels. Based on this work, we predict a bleak future for the flying squirrels, one which is closely associated with the fate of forests in Asia.
... Other taxa (e.g., arthropods, birds, fish, parasites, and plants) also exhibit broad Holarctic distributions (Fedorov et al. 2008;Haukisalmi et al. 2004Haukisalmi et al. , 2009Hewitt 2004;Waltari et al. 2007b). Distinctive phylogeographic breaks are common among high-latitude mammals including an east-west split in the vicinity of the Ural Mountains of western Russia (Brunhoff et al. 2003;Deffontaine et al. 2005;Fedorov et al. 1999aFedorov et al. , 1999b; splits between the major river basins of the Ob, Yenisei, Lena, and Kolyma Galbreath and Cook 2004;Fedorov et al. 2008); the Beringian refugium (Eddingsaas et al. 2004;Galbreath and Cook 2004;Waltari et al. 2004); and parts of Maritime Northeast Asia including Primorsky Krai, Japan, and the Korean Peninsula (Ehrich et al. 2008;Fedorov et al. 2008;Lee et al. 2008;Ohdachi et al. 2001;Yasuda et al. 2005). Other species exhibit a distinct barrier at the Bering Strait (Elias and Crocker 2008;Fedorov and Goropashnaya 1999). ...
... Bayesian phylogenetic analyses identified five well-supported lineages of collared lemming (Fig. 2). These lineages demonstrate the extensive genetic diversity of Late Pleistocene populations (Fig. S1), a distinct contrast to the genetically depauperate populations reported for this species at present (11). Ancient DNA studies have consistently reported postglacial loss of genetic diversity in northern Holarctic mammal species (12), including collared lemmings (13). ...
The Late Pleistocene global extinction of many terrestrial mammal species has been a subject of intensive scientific study for over a century, yet the relative contributions of environmental changes and the global expansion of humans remain unresolved. A defining component of these extinctions is a bias toward large species, with the majority of small-mammal taxa apparently surviving into the present. Here, we investigate the population-level history of a key tundra-specialist small mammal, the collared lemming (Dicrostonyx torquatus), to explore whether events during the Late Pleistocene had a discernible effect beyond the large mammal fauna. Using ancient DNA techniques to sample across three sites in North-West Europe, we observe a dramatic reduction in genetic diversity in this species over the last 50,000 y. We further identify a series of extinction-recolonization events, indicating a previously unrecognized instability in Late Pleistocene small-mammal populations, which we link with climatic fluctuations. Our results reveal climate-associated, repeated regional extinctions in a keystone prey species across the Late Pleistocene, a pattern likely to have had an impact on the wider steppe-tundra community, and one that is concordant with environmental change as a major force in structuring Late Pleistocene biodiversity.
... However, in situ survival of the lemming does not appear to be likely if the currrent ice sheet reconstructions are correct (Fig. 1). Many other recent studies have addressed molecular variation in various species of lemmings (true lemmings, Lemmus, and collared lemmings, Dicrostonyx; see e.g., Fedorov, 1999; Fedorov & al., 1999a, b; Fedorov & Goropashnaya, 1999; Ehrich & al., 2000; Fedorov & Stenseth, 2002), but only few of these studies have included material from the North Atlantic. The analysis of the arctic collared lemmings by Fedorov & Goropashnaya (1999) was circumarctic, but was also based on limited sampling from the North Atlantic. ...
Up to the 1960s, there was nearly complete consensus that disjunctions and endemism in the North Atlantic cannot be explained without �in situ� survival during the glaciations (the nunatak hypothesis). The alternative �tabula rasa� hypothesis of postglacial immigration was regarded to be of merely historical interest. Herein we review recent geological, molecular, taxonomic, and biogeographic data to re-examine this view. There is now strong geological evidence for some ice-free North Atlantic areas within the maximum limits of the Late Weichselian/Wisconsian ice sheets, but no fossils have been found to prove continuous �in situ� existence of life in these areas. Molecular data suggest that many plants and animals have migrated recently across the Atlantic, even if they lack mechanisms promoting long-distance dispersal. In other species, there are deep trans-oceanic phylogeographic splits suggesting survival in two or more refugia, but these refugia may have been located outside the ice sheets. Fo
... To increase the sample size for demographic analyses, additional (20-40) snap traps were placed in patches with potential lemming activity. We have also included snap traps set for genetic analyses in places with indications of lemming activity (Fedorov et al. 1999). This resulted in an average of 164 extra trap-nights at each site (range = 48-331, SD = 63). ...
The Swedish Tundra Northwest Expedition of 1999 visited 17 sites throughout the Canadian Arctic. At 12 sites that were intensively sampled we estimated the standing crop of plants and the densities of herbivores and predators with an array of trapping, visual surveys, and faecal-pellet transects. We developed a trophic-balance model using ECOPATH to integrate these observations and determine the fate of primary and secondary production in these tundra ecosystems, which spanned an 8-fold range of standing crop of plants. We estimated that about 13% of net primary production was consumed by herbivores, while over 70% of small-herbivore production was estimated to flow to predators. Only 9% of large-herbivore production was consumed by predators. Organization of Canadian Arctic ecosystems appears to be more top-down than bottom-up. Net primary production does not seem to be herbivore-limited at any site. This is the first attempt to integrate trophic dynamics over the entire Canadian Arctic.
... This pattern is similar to that found in the lesser white–fronted goose. Phylogeographic breaks in Yamal–Taimyr area have been also found in Arctic lemmings (Lemmus, Dicrostonyx; Fedorov et al. 1999 Fedorov et al. , 2003 ). Together these congruent patterns suggest that a glacial or other barrier existed in Yamal–Taimyr area during the last ice age. ...
The lesser white-fronted goose is a sub-Arctic species with a currently fragmented breeding range, which extends from Fennoscandia to easternmost Siberia. The population started to decline at the beginning of the last century and, with a current world population estimate of 25,000 individuals, it is the most threatened of the Palearctic goose species. Of these, only 30–50 pairs breed in Fennoscandia. A fragment of the control region of mtDNA was sequenced from 110 individuals from four breeding, one staging and two wintering areas to study geographic subdivisions and gene flow. Sequences defined 15 mtDNA haplotypes that were assigned to two mtDNA lineages. Both the mtDNA lineages were found from all sampled localities indicating a common ancestry and/or some level of gene flow. Analyses of molecular variance showed significant structuring among populations (
ST 0.220, P < 0.001).="" the="" results="" presented="" here="" together="" with="" ecological="" data="" indicate="" that="" the="" lesser="" white-fronted="" goose="" is="" fragmented="" into="" three="" distinctive="" subpopulations,="" and="" thus,="" the="" conservation="" status="" of="" the="" species="" should="" be="">
... ion of badgers. It is known that geographical barriers such as the Ural Mountains may have blocked east-or westward migrations of some mammals. This fairly widespread phylogeographic model has been identified among a number of mammal species, such as the root vole (Microtus oeconomus, Brunhoff et al., 2003), the collared lemmings (Dicrostonyx spp., Fedorov et al., 1999) and the common vole (Microtus arvalis, Haynes et al., 2003). ...
In the present study, to further understand the phylogenetic relationships among the Eurasian badgers (Meles, Mustelidae, Carnivora), which are distributed widely in the Palearctic, partial sequences of the mitochondrial DNA (mtDNA) control region (539-545 base-pairs) as a maternal genetic marker, and the sex-determining region on the Y-chromosome gene (SRY: 1052-1058 base-pairs), as a paternal genetic marker, were examined. The present study revealed ten SRY haplotypes from 47 males of 112 individuals of the Eurasian Continent and Japan. In addition, 39 mtDNA haplotypes were identified from those animals. From the phylogeography of both the uniparentally inherited genes, four lineages were recognized as Japanese, eastern Eurasian, Caucasian, and western Eurasian. The distribution patterns of the mtDNA lineages showed the existence of a sympatric zone between the eastern and western Eurasian lineages around the Volga River in western Russia. Furthermore, the present study suggested that in the Japanese badgers, the larger genetic differentiation of the Shikoku population was attributable to geographic history in the Japanese islands.
An overview of the studies on the sets of chromosomes in Palaearctic mammals is presented, conducted by Russian karyologists who have made important contributions to the improvement of mammalian taxonomy. As for many mammalian species the process of speciation could have been associated with variability in the number and morphology of chromosomes, karyotypes are often used as diagnostic features of morphologically similar cryptic species (twin species). The prospects of cytogenetic research in the field of speciation are discussed, in particular, the selection-based reinforcement of reproductive isolation initiated by chromosomal rearrangements.
Background
Arvicoline rodents are one of the most speciose and rapidly evolving mammalian lineages. Fossil arvicolines are also among the most common vertebrate fossils found in sites of Pliocene and Pleistocene age in Eurasia and North America. However, there is no taxonomically robust, well-supported, time-calibrated phylogeny for the group.
Methods
Here we present well-supported hypotheses of arvicoline rodent systematics using maximum likelihood and Bayesian inference of DNA sequences of two mitochondrial genes and three nuclear genes representing 146 (82% coverage) species and 100% of currently recognized arvicoline genera. We elucidate well-supported major clades, reviewed the relationships and taxonomy of many species and genera, and critically compared our resulting molecular phylogenetic hypotheses to previously published hypotheses. We also used five fossil calibrations to generate a time-calibrated phylogeny of Arvicolinae that permitted some reconciliation between paleontological and neontological data.
Results
Our results are largely congruent with previous molecular phylogenies, but we increased the support in many regions of the arvicoline tree that were previously poorly-sampled. Our sampling resulted in a better understanding of relationships within Clethrionomyini, the early-diverging position and close relationship of true lemmings ( Lemmus and Myopus ) and bog lemmings ( Synaptomys ), and provided support for recent taxonomic changes within Microtini. Our results indicate an origin of ∼6.4 Ma for crown arvicoline rodents. These results have major implications (e.g., diversification rates, paleobiogeography) for our confidence in the fossil record of arvicolines and their utility as biochronological tools in Eurasia and North America during the Quaternary.
Abstract—The M1
anterior lobe is a conservative element of the chewing surface not only in collared lem�mings (Dicrostonyx), but also in the entire subfamily Arvicolinae. A description of deviations from the typical
shape of the M1
anterior lobe in Dicrostonyx and the determination of the nature of inheritance from material
from laboratory colonies is given in this work. The phenotypes of the atypical form differ in the degree of
complexity. Individuals with an atypical anterior lobe shape are recessive homozygotes. Which phenotype
recessive homozygotes realize may depend on various factors, such as the litter number or the frequency of
males in the family. Most likely, these factors can interact in their influence on the frequency of manifestation
of recessive homozygotes. The polymorphism of the studied trait has a significant evolutionary potential and
opens up a new direction of evolutionary transformations of the chewing surface of molars in the subfamily
Arvicolinae.
https://rdcu.be/cWUHv
Dicrostonyx has been reported from seven Late Pleistocene localities in Wyoming. All localities are stratified, highly fossiliferous and detail a similar sequence of faunal changes through the late Pleistocene and early Holocene. Three of these are found in the northern Bighorn Mountains: Natural Trap Cave, Prospects Shelter and Shutdown Shelter. Little Box Elder and Bell Caves are found in the Laramie Range while Little Canyon Creek Cave and Bush Shelter are found in the southern Bighorn Mountains. These latter four localities contain sizable samples of Dicrostonyx teeth which have not been previously described. All four of these faunas date older than 12,000 years B.P. A review of the physiology of Dicrostonyx shows the genus is adapted to cold, moist climates and should not be used as an indicator of an environment similar to the modern High Arctic tundra. Preliminary examination of occlusal surfaces of Dicrostonyx teeth from these four localities suggests a taphonomy resulting from both diurnal and nocturnal birds of prey, similar to studies on the Dicrostonyx remains from Natural Trap Cave. There remains a slight possibility for at least some of the Dicrostonyx remains to be accumulated due to mammalian carnivore predation.
The complete mitochondrial genome the Eurasian collared lemming was obtained by using PCR amplification and capillary sequencing (GenBank accession no. KX066190). The collared lemming mitochondrial genome is 16,340 bp long and shows the gene order, contents and gene strand asymmetry typical for mammals. The mitogenome sequence provides an important new genomic resource for the collared lemming, which is a model study species in Arctic phylogeography and biotic history.
Recent palaeogenetic studies indicate a highly dynamic history in collared lemmings (Dicrostonyx spp.), with several demographical changes linked to climatic fluctuations that took place during the last glaciation. At the western range margin of D. torquatus, these changes were characterized by a series of local extinctions and recolonizations. However, it is unclear whether this pattern represents a local phenomenon, possibly driven by ecological edge effects, or a global phenomenon that took place across large geographical scales. To address this, we explored the palaeogenetic history of the collared lemming using a next-generation sequencing approach for pooled mitochondrial DNA amplicons. Sequences were obtained from over 300 fossil remains sampled across Eurasia and two sites in North America. We identified five mitochondrial lineages of D. torquatus that succeeded each other through time across Europe and western Russia, indicating a history of repeated population extinctions and recolonizations, most likely fromeastern Russia, during the last 50 000 years. The observation of repeated extinctions across such a vast geographical range indicates large-scale changes in the steppe-tundra environment in western Eurasia during the last glaciation. All Holocene samples, from across the species’ entire range, belonged to only one of the five mitochondrial lineages. Thus, extant D. torquatus populations only harbour a small fraction of the total genetic diversity that existed across different stages of the Late Pleistocene. In North American samples, haplotypes belonging to both D. groenlandicus and D. richardsoni were recovered from a Late Pleistocene site in south-western Canada. This suggests that D. groenlandicus had a more southern and D. richardsoni a more northern glacial distribution than previously thought. This study provides significant insights into the population dynamics of a small mammal at a large geographical scale and reveals a rather complex demographical history, which could have had bottom-up effects in the Late Pleistocene steppe-tundra ecosystem.
Recent palaeogenetic studies indicate a highly dynamic history in collared lemmings (Dicrostonyx spp.), with several demographical changes linked to climatic fluctuations that took place during the last glaciation. At the western range margin of D. torquatus, these changes were characterized by a series of local extinctions and recolonizations. However, it is unclear whether this pattern represents a local phenomenon, possibly driven by ecological edge effects, or a global phenomenon that took place across large geographical scales. To address this, we explored the palaeogenetic history of the collared lemming using a next-generation sequencing approach for pooled mitochondrial DNA amplicons. Sequences were obtained from over 300 fossil remains sampled across Eurasia and two sites in North America. We identified five mitochondrial lineages of D. torquatus that succeeded each other through time across Europe and western Russia, indicating a history of repeated population extinctions and recolonizations, most likely from eastern Russia, during the last 50 000 years. The observation of repeated extinctions across such a vast geographical range indicates large-scale changes in the steppe-tundra environment in western Eurasia during the last glaciation. All Holocene samples, from across the species' entire range, belonged to only one of the five mitochondrial lineages. Thus, extant D. torquatus populations only harbour a small fraction of the total genetic diversity that existed across different stages of the Late Pleistocene. In North American samples, haplotypes belonging to both D. groenlandicus and D. richardsoni were recovered from a Late Pleistocene site in south-western Canada. This suggests that D. groenlandicus had a more southern and D. richardsoni a more northern glacial distribution than previously thought. This study provides significant insights into the population dynamics of a small mammal at a large geographical scale and reveals a rather complex demographical history, which could have had bottom-up effects in the Late Pleistocene steppe-tundra ecosystem.
The Tamarisk Gerbil {Meriones tamariscinus) , widely distributed in Central Asia desert, also is found in arid western Mongolia-Xinjiang region of China. In the present study, we combined the mitochondrial Cyt b gene (1 140 bp) and D-loop control regions (429 bp) , a total of 1 569 bp, as molecular markers. Based on mtDNA sequence analyses, we calculated the nucleotide diversity, haplotype diversity and phylogeographic structure of the local populations, then discussed the geographical differentiation of the species. We detected 142 variable sites (9.05% of the total sequence) from 45 samples, including 34 single-state sites and 108 parsimony informative sites. No base insertions or deletions were detected. A total of 33 haplotypes were defined. Haplotype-based phylogenetic tree and haplotype network showed the 45 tamarisk gerbils clustered into two branches, of which the Hi Basin branch was the more primitive one. The divergence time for these two branches was 0. 24 Ma years ago, about in the Lushan glaciation. The population had a rapid recession in the past 15 000 years, probably a result of the Last Glacial Maximum. Based on the phylogeographic patterns inferred from the genetic variation in mtDNA Cyt b gene and D-loop region, we suggest that the population in the Hi Basin should belong in M. t. jaxartensis, and those in Jungar Basin, Gansu, and Inner Mongolia should be regarded as M. t. salchouensis.
Up to the 1960s, there was nearly complete consensus that disjunctions and endemism in the North Atlantic cannot be explained without in situ survival during the glaciations (the "nunatak hypothesis"). The alternative " tabula rasa hypothesis" of postglacial immigration was regarded to be of merely historical interest. Herein we review recent geological, molecular, taxonomic, and biogeographic data to re‐examine this view. There is now strong geological evidence for some ice‐free North Atlantic areas within the maximum limits of the Late Weichselian/Wisconsian ice sheets, but no fossils have been found to prove continuous in situ existence of life in these areas. Molecular data suggest that many plants and animals have migrated recently across the Atlantic, even if they lack mechanisms promoting long‐distance dispersal. In other species, there are deep trans‐oceanic phylogeographic splits suggesting survival in two or more refugia, but these refugia may have been located outside the ice sheets. For vascular plants, we provide an updated list of 77 north boreal, alpine, and arctic taxa accepted as North Atlantic endemics. The degree of endemism is very low (0.0‐1.9% single‐region endemism). Forty endemics occur in more than one of the isolated Atlantic regions, indicating extensive migration and complicating inferences on the location of refugia. Thirty‐four endemics are probably not hardy enough for nunatak survival and are explained by postglacial immigration (or in situ evolution). Among the 43 "hardy" endemics, there is not a single outcrossing diploid that could suggest long‐term evolution. Most of the hardy endemics are asexual or self‐fertilizing polyploids, some of postglacial hybrid origin. Others are preglacial polyploids which immigrated postglacially or survived in situ . Some ice‐free areas, such as the extensive Greenlandic ones, may have supported survival of some hardy organisms. The evidence accumulated since the 1960s suggests, however, that endemism and disjunctions in the North Atlantic can be explained without invoking in situ glacial survival.
The geographic pattern of mtDNA variation in lemmings from 13 localities throughout the Eurasian Arctic was studied by using eight restriction enzymes and sequencing of the cytochromebregion. These data are used to reveal the vicariant history ofLemmus, and to examine the effect of the last glaciation on mtDNA variation by comparing diversity in formerly glaciated areas to the diversity in non-glaciated areas. Phylogenetic congruence across different Arctic taxa and association between observed discontinuities, and probable Pleistocene barriers, suggest that glacial-interglacial periods were crucial in the vicariant history ofLemmus. Differences in amount of divergence (2.1–9.1%) across different historical barriers indicate chronologically separate vicariant events during the Quaternary. Populations from a formerly glaciated area are no less variable than those in the non-glaciated area. Regardless of glaciation history, no population structure and high haplotype diversity were found within geographic regions. The lack of population structure indicates that populations with high ancestral haplotype diversity shifted their distribution during the Holocene, and that lemmings tracked a changing environment during the Quaternary without reduction of effective population size.
The variation of molar patterns and lower jaw of collared lemmings from the Bolshevik Island is analyzed. In all teeth except m2 the morphotype henseli is dominant. Morphotype simplicior is the second most common morphotype in M3. Such type of dentition was typical for the lemmings of the Late Pleistocene and within the recent collared lemmings of Palaearctic was not recorded until now. Morphotype variation in the sample from Bolshevik Island is most similar to that in the sample from the Late Pleistocene Betovo site (36 thousand years BP). By the structure of the lower jaw lemmings from Bolshevik Island differ both from all recent subspecies of the genus, known karyomorphs, mtDNA phylogroups, and lemmings from Betovo. KEY WORDS: collared lemmings, Pleistocene, Severnaya Zemlya, molar patterns variation, morphometric variation, intraspecies taxonomy. Natalya I. Abramson [lemmus@zin.ru], Zoological Institute, Russian Academy of Science, Universitetskaya nab. 1, St. Petersburg 199034, Russia; Nikolai G. Smirnov [nsmirnov@ecology.uran.ru], Institute of Plant and Animal Ecology, Russian Academy of Science, ul. Vosmogo Marta 202, Yekaterinburg 620144, Russia; Elena P. Tikhonova [ellobius@zin.ru], Zoological Institute, Russian Academy of Science, Universitetskaya nab. 1, St. Petersburg 199034, Russia. Ìîðôîëîãè÷åñêîå èçó÷åíèå êîïûòíîãî ëåììèíãà (Rodentia, Arvicolidae, Dicrostonyx) îñòðîâà Áîëüøåâèê àðõèïåëàãà Ñåâåðíàÿ Çåìëÿ, ñ çàìåòêàìè ïî ýâîëþöèè è òàêñîíîìè÷åñêîìó ïîëîaeåíèþ Í.È. Àáðàìñîí, Í.Ã. Ñìèðíîâ, Å.Ï. Òèõîíîâà ÐÅÇÞÌÅ. Èçó÷åíà èçìåí÷èâîñòü çóáíîé ñèñòåìû è íèaeíåé ÷åëþñòè êîïûòíûõ ëåììèíãîâ ñ î-âà Áîëüøåâèê. Ó ëåììèíãîâ ñ î-âà Áîëüøåâèê íà âñåõ çóáàõ, çà èñêëþ÷åíèåì âòîðîãî íèaeíåãî, ïðåîáëàäàë ìîðôîòèï henseli, íà âòîðîì ìåñòå áûë ìîðôîòèï simplicior. Ñðåäè ñîâðåìåííûõ êîïûòíûõ ëåììèíãîâ Åâðàçèè òàêîãî ñòðîåíèÿ çóáíîé ñèñòåìû äî ñèõ ïîð íå áûëî îòìå÷åíî, â òî âðåìÿ êàê äëÿ ëåììèíãîâ ïîçäíåãî ïëåéñòîöåíà îíî áûëî òèïè÷íûì. Ïîêàçàíî, ÷òî ïî íàáîðó ìîðô íà ïåðâîì è âòîðîì âåðõíèõ çóáàõ âûáîðêà ñîâðåìåííûõ ëåììèíãîâ ñ î-âà Áîëüøåâèê â íàèáîëüøåé ñòåïåíè ñõîäíà ñ òàêîâûì ó ëåììèíãîâ èç ïîçäíåïëåéñòîöåíîâîãî ìåñòîíàõîaeäåíèÿ Áåòîâî (36 òûñ. ëåò), ÷òî ïîçâîëÿåò ñ÷èòàòü èõ ðåëèêòàìè ïîñëåäíåé ëåäíèêîâîé ýïîõè. Ïî ñòðîåíèþ íèaeíåé ÷åëþñòè ëåììèíãè ñ î-âà Áîëüøåâèê îòëè÷àþòñÿ äîñòîâåðíî êàê îò âñåõ ñîâðåìåííûõ ïîäâèäîâ, òàê è îò ëåììèíãîâ èç ìåñòîíàõîaeäåíèÿ Áåòîâî. ÊËÞ×ÅÂÛÅ ÑËÎÂÀ: êîïûòíûå ëåììèíãè, ïëåéñòîöåí, Ñåâåðíàÿ Çåìëÿ, ìîðôîòèïè÷åñêàÿ èçìåí-÷èâîñòü, ìîðôîìåòðè÷åñêàÿ èçìåí÷èâîñòü, âíóòðèâèäîâàÿ òàêñîíîìèÿ.
The geographic pattern of mtDNA variation in lemmings from 13 localities throughout the Eurasian Arctic was studied by using eight restriction enzymes and sequencing of the cytochrome b region. These data are used to reveal the vicariant history of Lemmus, and to examine the effect of the last glaciation on mtDNA variation by comparing diversity in formerly glaciated areas to the diversity in non‐glaciated areas. Phylogenetic congruence across different Arctic taxa and association between observed discontinuities, and probable Pleistocene barriers, suggest that glacial‐interglacial periods were crucial in the vicariant history of Lemmus. Differences in amount of divergence (2.1–9.1%) across different historical barriers indicate chronologically separate vicariant events during the Quaternary. Populations from a formerly glaciated area are no less variable than those in the non‐glaciated area. Regardless of glaciation history, no population structure and high haplotype diversity were found within geographic regions. The lack of population structure indicates that populations with high ancestral haplotype diversity shifted their distribution during the Holocene, and that lemmings tracked a changing environment during the Quaternary without reduction of effective population size.
The present study reviews the taxonomy of anoplocephalid cestodes of collared lemmings (Dicrostonyx spp.) and describes the patterns of cestode biogeography in the Holarctic region. The morphological differentiation of cestode species is augmented with a genetic differentiation based on three independent markers. We show that collared lemmings are parasitized by five host-specific species of Paranoplocephala, three of which are described here as new P. arctica (Rausch, 1952), P. alternata sp. nov., P. serrata Haukisalmi & Henttonen, 2000,P. nordenskioeldi sp. nov. and P. krebsi sp. nov. The redescription of P. arctica shows that the original description of this species is composite. Paranoplocephala alternata, P. serrata and P. nordenskioeldi are shown to have a Holarctic distribution, whereas P. arctica and P. krebsi are restricted to the Nearctic region, including Wrangel Island. It is suggested that the Holarctic species colonized North America concomitantly with their hosts and that the appearance of the Nearctic species is connected with the subsequent divergence of collared lemmings in North America. Geographical distribution and sequence data for the first transcribed spacer (ITS1) of nuclear rDNA show thatP. alternata and P. arctica are sister taxa and that the latter species probably diverged from P. alternata in eastern Beringia. Other phylogenetic relationships among cestode species remained largely unsettled.
Research into the geographical pattern of tooth size in the red fox, Vulpes vulpes (Linnaeus, 1758) in the Holarctic was conducted on a sample of 3806 skulls belonging to 41 fox populations. The Nearctic was represented by 948 specimens (249 females, 359 males, 340 specimens of unknown sex) belonging to 13 populations, whereas the Palearctic was represented by 2858 red foxes (1034 females, 1256 males, 568 specimens of unknown sex) from 32 populations. In the Nearctic, the largest foxes live on Kodiak Island (V. v. harrimani) and the Kenai Peninsula (V. v. kenaiensis), while the smallest ones live in California (V. v. necator) and Georgia (V. v. fulvus). In the Palearctic, the largest foxes come from the Far East (V. v. jakutensis, V. v. beringiana, V. v. tobolica), while the smallest are from the southern borders of the Eurasian range (V. v. pusilla, V. v. barbara, V. v. arabica). In both the Palearctic and Nearctic, tooth size in the fox varies depending on the geo-climatic factors. The fox's tooth size confirms the general basis of Bergmann's rule. In the Palearctic, specimens with larger teeth occur in cooler habitats with greater seasonality. These are first and foremost Northern and Far Eastern populations. In the Nearctic, tooth size in red foxes depends on the temperature and humidity of their habitat. Competition within the species and between species has important impact on the variation and dimorphism of tooth size in the red fox. Both in the Nearctic and Palearctic, red foxes from regions of sympatric co-occurrence with other closely related Vulpes species, are more sexually dimorphic in terms of tooth size than red foxes from allopatric regions. Analysis of morphological distance on the basis of the size of dental characteristics shows, that in the Palearctic, the foxes from India (V. v. pusilla), while in the Nearctic, the population from Kodiak Island (V. v. harrimani) are most distant from the remaining populations. Geographic barriers such as the Bering Strait, Parry Channel, Mackenzie River, Kolyma and Omolon River systems have had a critical impact on red fox evolution. The most likely place for the evolution and diversification of the phyletic line Vulpes vulpes seems to be the Middle East region.
To. test for isolation by mountain ranges in small arboreal mammals, phylogeography of Pallas's squirrel .Callosciurus erythraeus) was investigated using complete mitochondrial control region sequences (1,079–1,081 bases). This common species is distributed in the low and middle elevations of Taiwan, Republic of China. We examined 71 specimens from 6 sites in 3 study regions divided by mountain ranges in Taiwan. The 43 haplotypes found in the Taiwan populations revealed association with geography. There were 4 main mitochondrial DNA phylogroups (northern, western, southern, and eastern), but 4 haplotypes were not included in any phylogroup. Distribution range of each phylogroup was similar to defined geological categories, suggesting mountain range isolation influenced populations of C. erythraeus. The 4 phylogroups may be the result of glacial refugia during the Pleistocene.
The brown hareLepus europaeus Pallas, 1778 occurs naturally in central Eurasia, but has been introduced to parts of northern Europe, South- and North America,
Australia and New Zealand. Brown hares were introduced to Sweden from central Europe for hunting purposes during the 19th
century. We investigated how the human--mediated brown hare colonisation of Sweden is reflected in the amount of genetic variation
present by assessing variation and composition of mitochondrial DNA (mtDNA) lineages among Swedish brown hares. MtDNA from
a total of 40 brown hare specimens from 15 localities were analysed for Restriction Fragment Length Polymorphisms. The haplotype
diversity is surprisingly high (0.893 ± 0.002) when compared to the mtDNA diversity among brown hares on the European continent
as well as to other mammalian species. Admixture of haplotypes from different source populations combined with a reduced effect
of random genetic drift and a relaxed selection pressure due to rapid population growth after introduction are mechanisms
that are likely to account for the observed high mtDNA haplotype diversity.
The Late Pleistocene global extinction of many terrestrial mammal
species has been a subject of intensive scientific study for over a
century, yet the relative contributions of environmental changes
and the global expansion of humans remain unresolved. A defining
component of these extinctions is a bias toward large species, with
the majority of small-mammal taxa apparently surviving into the
present. Here, we investigate the population-level history of a key
tundra-specialist small mammal, the collared lemming (Dicrostonyx
torquatus), to explore whether events during the Late Pleistocene
had a discernible effect beyond the large mammal fauna. Using
ancient DNA techniques to sample across three sites in North-West
Europe, we observe a dramatic reduction in genetic diversity in this
species over the last 50,000 y. We further identify a series of extinction-
recolonization events, indicating a previously unrecognized
instability in Late Pleistocene small-mammal populations,
which we link with climatic fluctuations. Our results reveal climateassociated,
repeated regional extinctions in a keystone prey species
across the Late Pleistocene, a pattern likely to have had an impact
on the wider steppe-tundra community, and one that is concordant
with environmental change as a major force in structuring Late
Pleistocene biodiversity.
The biogeographic groups of rodent (arvicoline) and beetle species in the modern fauna of the Urals and Western Siberia based on the longitudinal patterns of their present-day distribution are established. Occurrence of species of the Transpalearctic, West Palearctic (European), East-Palearctic, and Central-Palearctic faunal groups is estimated at different stages of the Late Quaternary development of the present-day fauna of the region. The border between the European and East-Palearctic faunal groups represents a vast territory where the ranges of the species included in those groups intersect. The border territory includes the Ural Mountains and the lowlands lying west and east of it (the East-European Plain and the West Siberian Plain). The biomes of those territories represent the North-Eurasian corridors providing migrations of species from the different faunal complexes in the west–east, east–west, and north–south directions. The importance of the study area for faunal correlations throughout the continent is determined by presence of the key arvicoline taxa traditionally used for correlation purposes (taxa Dicrostonyx, Lagurus, Microtus gregalis), and by the gradual change in faunal composition along the latitudinal gradient of environment at any given stage of the Quaternary. Transzonal faunal correlations within the Urals and Western Siberia integrating the evolutionary morphological studies of the key taxa and assessment of the faunal successions may serve as a basis for Trans-Eurasian correlation.
Andrya arctica is a cestode parasite of the family Anoplocephalidae (Cyclophyllidea), parasitizing lemmings of the genus Dicrostonyx throughout the Holarctic region. The population structure of this intestinal parasite was studied from eight different regions, six of which represented different genetic entities of lemming hosts. Molecular sequence tagged site markers and minisatellite fingerprints as well as morphology and morphometries were used to reveal the population structure of A. arctica in the Holarctic region. The results suggest that the evolutionary history of this cestode species has included different processes acting on different geographical regions. On the Siberian mainland (host D. torquatus), the division of the parasites into different genetic entities agreed perfectly with the chromosomal races of the lemming hosts that points towards a shared evolutionary history between the host and the parasite (‘cospeciation’). The main phylogenetic split of Dicrostonyx between Eurasia and North America was not, however, observed in A. arctica. This suggests that in the Nearctic (host D. groenlandicus) the parasite has remained relatively unmodified because of the large cohesive populations (‘coadaptation’). The uniqueness of the Greenland population, and possibly also that of the Wrangel Island, can be explained by peripheral isolation, refugial effects or founder effects.
Aim It has been proposed that the root vole subspecies, Microtus oeconomus finmarchicus , survived the last glacial period on islands on the north‐west coast of Norway. The Norwegian island of Andøya may have constituted the only site with permanent ice‐free conditions. Geological surveys and fossil finds from Andøya demonstrate that survival throughout the last glacial maximum was probably possible for some plants and animals. In this study we aim to infer the recent evolutionary history of Norwegian root vole populations and to evaluate the glacial survival hypothesis.
Methods DNA sequence variation in the mitochondrial cytochrome b gene was studied in 46 root voles from 19 localities.
Location Northern Fennoscandia and north‐west Russia with a focus on islands on the north‐west coast of Norway.
Results The phylogeographical analyses revealed two North European phylogroups labelled ‘Andøya’ and ‘Fennoscandia’. The Andøya phylogroup contained root voles from the Norwegian islands of Andøya, Ringvassøya and Reinøya and two localities in north‐west Russia. The Fennoscandian phylogroup encompassed root voles from the three Norwegian islands of Kvaløya, Håkøya and Arnøya and the remaining specimens from Norway, northern Sweden and Finland. Nucleotide diversity within the Andøya and Fennoscandian phylogroups was similar, ranging from 0.5% to 0.7%.
Main conclusions Both our genetic data and previously published morphological data are consistent with in situ glacial survival of root voles on Andøya during the last glacial maximum. However, the level of genetic diversity observed in the extant island populations, the past periods of severe climatic conditions on Andøya and the ecology of the root vole are somewhat difficult to reconcile with this model. A biogeographical scenario involving late glacial recolonization along the northern coasts of Russia and Norway therefore represents a viable alternative. Our results demonstrate that complex recolonization and extinction histories can generate intricate phylogeographical patterns and relatively high levels of genetic variation in northern populations.
A range-wide phylogeographic study of the tundra shrew (Sorex tundrensis) was performed using cytochrome b and cytochrome oxidase I (COI) mitochondrial genes. The results based on 121 specimens from 42 localities demonstrate that the tundra shrew is divided into five main mitochondrial DNA phylogenetic lineages with largely parapatric distribution. In addition to a single Nearctic clade (Alaska) four Palearctic clades are identified: Western (Northen Urals, Kazakhstan, South-West Siberia), Eastern (from East Transbaikalia and the Middle Amur to Chukotka), South Central (Central Siberia, the Altai, the Dzhungarian Alatau) and North Central (Northern Siberia, Central Yakutia). Date estimates obtained by use of a molecular clock corrected for potential rate decay suggest Late Pleistocene age for the most recent common ancestor of all contemporary tundra shrew populations. Relatively high genetic divergence between phylogroups (0.95–1.6%) indicates that the observed phylogeographic structure was initiated by historical events that predated the Last Glacial Maximum. We assume that, being more cold- and arid-tolerant, tundra shrew underwent expansion during an early cold phase of the Last Glacial and spread through its recent range earlier than most of other Siberian red-toothed shrews. Comparative phylogeographic analysis of Siberian shrews and rodents suggests that evolutionary histories of species associated with azonal or open habitats show important differences compared to forest species. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101, 721–746.
We analysed variation of the mitochondrial control region from willow tits through its Palaearctic distribution range. Although we found high amount of genetic variation (π=1.114%), there was almost no differentiation between subspecies or geographical localities. This may be because of a combination of several ecological and genetic factors, including a relatively homogenic habitat through the distribution range, lack of geographical barriers, high gene flow and a large long-term effective population size. On the contrary, in the songar tit, which is sometimes considered to be conspecific with the willow tit, the mitochondrial lineages seem to correlate with the geographical locality and are clearly distinct from the willow tit. We concluded that the common ancestors of willow and songar tits existed some 1.5–2 Myr ago in the south-eastern Asia. After the last Ice Ages, the willow tit expanded all through the Palaearctic, whereas the songar tit remained in eastern Asia.
Lemmings are a classic example of animals with strong population cycles. High-amplitude density fluctuations with low numbers during the low phase are expected to lead to strong genetic drift, which erodes genetic variability. By compiling data on mitochondrial DNA polymorphism for 72 lemming populations from 5 species, we found no evidence for this erosive mechanism. On the contrary, high levels of haplotype diversity (average h of 0.75 for samples of the genus Lemmus) were observed in many populations. Although the effective size determines the level of genetic diversity in closed populations, diversity is primarily determined by immigration in open populations. Simulations of genetic drift in open populations fluctuating in density confirmed the independence of genetic variability from local effective size, and predicted a deficit of rare alleles, as observed in lemming samples. High genetic variability thus implies high gene flow over a considerable area for lemmings, but does not provide information about the local effective size of populations. Examination of empirical data suggests that high genetic diversity may be the rule rather than the exception in cyclic populations.
The present study reviews the taxonomy of anoplocephalid cestodes of collared lemmings (Dicrostonyx spp.) and describes the patterns of cestode biogeography in the Holarctic region. The morphological differentiation of cestode species is augmented with a genetic differentiation based on three independent markers. We show that collared lemmings are parasitized by five host-specific species of Paranoplocephala, three of which are described here as new: P. arctica (Rausch, 1952), P. alternata sp. nov., P. serrata Haukisalmi & Henttonen, 2000, P. nordenskioeldi sp. nov. and P. krebsi sp. nov. The redescription of P. arctica shows that the original description of this species is composite. Paranoplocephala alternata, P. serrata and P. nordenskioeldi are shown to have a Holarctic distribution, whereas P. arctica and P. krebsi are restricted to the Nearctic region, including Wrangel Island. It is suggested that the Holarctic species colonized North America concomitantly with their hosts and that the appearance of the Nearctic species is connected with the subsequent divergence of collared lemmings in North America. Geographical distribution and sequence data for the first transcribed spacer (ITS1) of nuclear rDNA show that P. alternata and P. arctica are sister taxa and that the latter species probably diverged from P. alternata in eastern Beringia. Other phylogenetic relationships among cestode species remained largely unsettled.
Among recent lemmings (D. torquatus from the Yamal Peninsula and D. groenlandicus from Somerset, Bathurst, Melville, and Devon islands), there are populations with archaic sets of morphotypes characteristic of the end of the Late Pleistocene. In some parts of the species range, lemming morphotypes follow the pattern characteristic of the Holocene stage of their evolution. Lemmings with the best developed tooth system live in the Bering Sea sector of the Arctic (Wrangel Island, Chukotka and Alaska). The correspondence of the boundaries of the groups distinguished by odontological traits to the phylogeographic data on mitochondrial DNA (mtDNA) and chromosomal groups is discussed.
We compared mitochondrial DNA (mtDNA) restriction fragment profiles from samples of 13 bird species that occur on both sides of Beringia. All but two species, Lapland Longspur (Calcarius lapponicus) and Green-winged Teal (Anas crecca), exhibited evidence of genetic differentiation, albeit at varying degrees. Several species exhibited mtDNA differentiation consistent with species-level distinctness: Marbled Murrelet (Brachyramphus marmoratus), Three-toed Woodpecker (Picoides tridactylus), Whimbrel (Numenius phaeopus), Mew Gull (Larus canus), Black-billed Magpie (Pica pica), American Pipit (Anthus rubescens), and Rosy Finch (Leucosticte arctoa). Other species exhibited levels of mtDNA differentiation intermediate between populations and species: Barn Swallow (Hirundo rustica), Common Tern (Sterna hirundo), Common Snipe (Gallinago gallinago), and Pelagic Cormorant (Phalacrocorax pelagicus). Because of small sample sizes, we do not recommend formal taxonomic changes, although our data could be combined with other data to raise several taxa to species level. Our data do not indicate a consistent level of mtDNA differentiation between putatively conspecific populations on different sides of Beringia, suggesting different times of colonization or cessation of gene exchange. Most comparisons of birds within continents exhibit less mtDNA differentiation than our trans-Beringia comparisons, suggesting limited gene flow between continents.
UNDERSTANDING the environment of the Bering land bridge and determining
the timing of late Wisconsin inundation are important for several areas
of study. These include: (1) the timing of the re-establishment of
circulation between Pacific and Atlantic Oceans; (2) the timing of
development of a northern biotic refugium and the closing of the bridge
to species immigration; (3) Palaeoindian migration routes; and (4)
palaeotopographic data for atmospheric general circulation
models1. Late Wisconsin palaeobotanical and fossil insect
data from the central and northern sectors of the Bering land bridge
indicate widespread mesic shrub tundra environments even during the last
glacial maximum. Contrary to previous hypotheses, we found no evidence
of steppe tundra on the land bridge. New accelerator mass spectrometer
14C dates show much of the land bridge was above sea level
and thus available for human and animal migration until 11,000 yr BP.
Insect evidence suggests that summer temperatures at that time were
substantially warmer than now.
Mitochondrial DNA (mtDNA) from 99 meadow voles (Microtus pennsylvanicus) collected in 13 localities and from 2 Townsend's voles (M. townsendii) from a single locality was assayed for restriction fragment length polymorphism (RFLP) with 13 restriction endonucleases. There was evidence of extensive mtDNA sequence heterogeneity within and among meadow vole populations. Thirty-eight different mtDNA composite phenotypes were found. Two common mtDNA composite phenotypes were shared among five populations, the other mtDNA composite phenotypes being characteristic of individual populations. Estimates of nucleon diversity (ĥ) were high (0.303–0.893), as were measures of intrapopulational nucleotide divergence (px values ranged from 0.0 to 0.038). Population fluctuations and periodic dispersal are the likely mechanisms maintaining high mtDNA composite phenotype diversity in meadow vole populations. Overall interpopulational nucleotide divergence (pxy) was also high (values ranged from 0.007 to 0.045). Cluster analysis clearly separates M. pennsylvanicus and M. townsendii and suggests the separation of the meadow vole populations into eastern and central groups, but there is little evidence of structure within the regional groups. Based on the zoogeography of the populations sampled, the mtDNA RFLP data support the differentiation of Microtus pennsylvanicus into at least two previously described subspecies.
Genetic differentiation among populations and speciation in Dicrostonyx is hypothesized to have resulted from either allopatric divergence in glacial refugia during the Wisconsin or sympatric processes uncorrelated with refugial isolation. We examined chromosomal and mitochondrial DNA variation in four laboratory colonies, representing three species, in a preliminary evaluation of these hypotheses. Chromosomal variation is extensive among populations, diploid numbers ranging from 38 to 50. Autosomal variation appears to be due primarily to Robertsonian rearrangements and additions of supernumerary chromosomes, and is geographically unpatterned. Sex chromosome morphology is geographically structured and correlated with proposed southern and northern refugia. Restriction fragment analysis of mitochondrial DNA revealed two ancient, divergent genotypic assemblages, corresponding to geographic distributions of sex chromosomes. Autosomal variation, and any resulting reproductive isolation, probably is recent and uncorrelated with refugial history, whereas divergence of sex chromosomes and disparate mitochondrial assemblages likely predate the Wisconsin.
Concerns genetic variability in the nominate subspecies, O. d. dalli, from 3 parts of its N Alaskan distribution: the Alaskan Range, the Tanana Hills and the Brooks Range. These areas are 150-200 km apart. Their populations have been isolated from each other since the end of the Wisconsinan glaciation. -from Authors
We present here a framework for the study of molecular variation within a single species. Information on DNA haplotype divergence is incorporated into an analysis of variance format, derived from a matrix of squared-distances among all pairs of haplotypes. This analysis of molecular variance (AMOVA) produces estimates of variance components and F-statistic analogs, designated here as phi-statistics, reflecting the correlation of haplotypic diversity at different levels of hierarchical subdivision. The method is flexible enough to accommodate several alternative input matrices, corresponding to different types of molecular data, as well as different types of evolutionary assumptions, without modifying the basic structure of the analysis. The significance of the variance components and phi-statistics is tested using a permutational approach, eliminating the normality assumption that is conventional for analysis of variance but inappropriate for molecular data. Application of AMOVA to human mitochondrial DNA haplotype data shows that population subdivisions are better resolved when some measure of molecular differences among haplotypes is introduced into the analysis. At the intraspecific level, however, the additional information provided by knowing the exact phylogenetic relations among haplotypes or by a nonlinear translation of restriction-site change into nucleotide diversity does not significantly modify the inferred population genetic structure. Monte Carlo studies show that site sampling does not fundamentally affect the significance of the molecular variance components. The AMOVA treatment is easily extended in several different directions and it constitutes a coherent and flexible framework for the statistical analysis of molecular data.
Tiksi area in eastern Siberia has generally been believed to have remained ice-free throughout the entire Ice Age. However, new glacial geomorphological research in the region has revealed evidence of a former ice sheet centered on the East Siberian shelf and reaching as far as Tiksi Bay. Among indications supporting this concept are fresh-looking U-shaped valleys, giant flutes, rock drumlins and other ice-erosional features, as well as systems of glacio-tectonic ridges coupled with rock basins (“hill-and-hole pairs”)—all attesting to a former ice motion in a northeast-southwest direction.
The work carried out in May 1990 by a Swedish-Soviet field party was aimed at resolving the chronology of the latest glacial events in the Tiksi area. To this end, the bottom sediments of two lakes joined by glaciotectonic ridges were cored, analysed and AMS-¹⁴C dated. The ages of 6450+/-110 6870+/-80 and 8500+/-160 radiocarbon years BP were minimum dates obtained for the beginning of lacustrine sedimentation in the basins. This suggested that the last icesheet glaciation of the area had been of Late Pleistocene age.
The shrews of the Sorex araneus group have undergone a spectacular chromosome evolution. The karyotype of Sorex granarius is generally considered ancestral to those of Sorex coronatus and S. araneus. However, a sequence of 777 base pairs of the cytochrome b gene of the mitochondrial DNA (mtDNA) produces a quite different picture: S. granarius is closely related to the populations of S. araneus from the Pyrenees and from the northwestern Alps, whereas S. coronatus and S. araneus from Italy and the southern Alps represent two well-separated lineages. It is suggested that mtDNA and chromosomal evolution are in this case largely independant processes. Whereas mtDNA haplotypes are closely linked to the geographical history of the populations, chromosomal mutations were probably transmitted from one population to another. Available data suggest that the impressive chromosome polymorphism of this group is quite a recent phenomenon.
Substantiated cases of ring species in mammals are rare. I examined the variation in mitochondrial DNA (mtDNA) of Perognathus amplus and P. longimembris in and around Arizona to test the hypothesis proposed by Hoffmeister (1986) that these two taxa are members of a single ring species demonstrating circular overlap. Through digestion of purified mtDNA from 45 P. amplus and 35 P. longimembris with 16 type II restriction enzymes, I identified 38 distinct haplotypes that belong to eight different evolutionary lineages. I then amplified and directly sequenced a portion of the mitochondrial cytochrome-b region from individuals representative of the lineages identified by restriction fragments, and used these data for phylogeny reconstruction in both a parsimony and neighbor-joining setting. The resulting phylogeny was consistent with the ring hypothesis, but, based on the incompleteness of the ring of subspecies and the apparent timing of evolutionary events in this group, I conclude that P. amplus and P. longimembris are distinct lineages that have completed the speciation process.
From its inception in the latter half of this century, the field of molecular evolution has been dominated by a series of fundamental controversies about the nature and evolutionary significance of genetic variation. Underlying these debates (discussed later) were exciting conceptual issues that understandably captured the attention of molecular evolutionists. However, to a considerable degree these controversies also directed attention away from what often were perceived as more mundane applications of molecules as genetic markers. Thus, prior to the mid-1980s, with a few notable exceptions, most applications of molecular markers in areas of natural history or phylogenetic estimation were viewed as ancillary by-products of research programs whose main goals were to uncover genetic mechanisms or elucidate broad evolutionary processes. Only in the last few years has molecular phylogenetics per se begun to assume its appropriate status as an essential scientific discipline, both empirically rich and conceptually challenging. What were these broad controversies in evolutionary biology that so dominated attention, relegating molecular phylogenetics to the back burner? These historical debates are the primary subject of this chapter.
Two new species of collared lemmings from the Olyor suite of the Kolyma lowland fill an essential gap in the Early Pleistocene history of the tribe on account of their stratigraphic position and clear trend in molar evolution. P(?) compitalis sp.n., and P.hopkinsi are studied. Evolutionary changes in the dentition of Dicrostonychini show that it is more reliable to distinguish evolutionary stages and identify species on the basis of the structure of of their teeth. Each species in the line has a characteristic M1-2 morphotype. The complication of the molars progresses at a slower rate. Several species have overlapping ranges of variability in the structure of the lower molars. The continuous evolutionary history of collared lemmings in the climatic conditions of the Beringian subarctic, from the Pliocene down to the present, gives good grounds to consider the subarctic as the place of their origin.-from Author
From a study of the geographic occurrences of contemporary hybridization among North American animals, it has become apparent that most of the hybrids are produced in a few relatively localized zones, with little hybridizing in the vast areas between these zones of mixing. The hybrids tend to be at least moderately fertile and therefore to be a source of significant gene exchange between the typically allopatric pairs of species and semispecies. There is a wide variety of consequences from this introgression, with greater or lesser influence on the parental populations, and large portions of the fauna and probably flora are involved. An appropriate term for such a belt of interfaunal and interfloral linkage is suture-zone.1
Many descriptive models of chromosomal evolution have been formulated over the past two decades. We review the assumptions and predictions of these models and consider some pertinent evidence. One model of adaptive divergence, the canalization model, is difficult to test, and where predictions are explicitly stated, empirical data generally do not support the model. However, few adequate data sets are available to test this hypothesis, and it deserves further study. Several process-oriented models of chromosomal speciation are reviewed with respect to genetic isolating mechanisms, the fitness components of individual rearrangements, and the permissible population structures. From the last we attempt to estimate qualitatively the expected genetic correlates of each model to maximize its testability. Theoretical and empirical inadequacies are discussed and suggestions are made for improvement. Both phyletic and spe- ciation models of chromosomal evolution have often been based on broad comparative studies of large taxonomic groups, but more precise testing will require multidisciplinary population- level studies of organisms hypothesized to be undergoing some form of chromosomally-mediated speciation or adaptive radiation. (Chromosomes; canalization; speciation.)
Numerical phylogenetic analyses of G-banded karyotypes were carried out for 22 species of arvicolids belonging to eight genera
with diploid numbers among the species ranging from 18 to 64. Interspecific karyotypic comparisons indicate that 38 homologous
autosomes or autosomal arms are shared by two or more species. The additional presence of 33 unique elements and 141 euchromatic
rearrangements account for the extensive interspecific karyotypic variability. Ten different types of rearrangements were
documented with centric fusion (27.0%), tandem fusion (14.2%) and pericentric inversion (12.8%) being the most abundant. Chromosomes
and chromosomal rearrangements were quantitatively coded as present, absent, or missing in the karyotype of each species and
the resulting data matrix (22 species by 214 karyotypic characters) subjected to cladistic analyses (with Peromyscus as an outgroup). Six analyses were executed where chromosomal rearrangements were weighted equal to or less than the weights
assigned to entire chromosomes. Families of equally parsimonious trees were obtained and subsequently distilled into Adams-2
consensus estimates. Consistency indices ranged from 0.75 to 0.84 with reversals accounting for 2–30% of all homoplastic events.
Systematically, Clethrionomys, Lemtnus, Synaptomys, Lagurus, Neofiber, and six species of Microtus share generally primitive autosomal complements; however, four derived characters suggest a relationship between M. ochrogaster and M. pinetorum. Six other species of Microtus (townsendii, pennsylvanicus, breweri, montanus, canicaudus and the more distant oregoni) share a number of derived characters. Dicrostonyx, Phenacomys, M. longicaudus, and M. oeconomus each possess a series of uniquely derived characters that tend to isolate these lineages. Chromosomal collocations support
those derived from paleontology, comparative morphology, and protein electrophoresis in certain respects but not in others.
Comparisons of zoogeographic distributions among four pairs of chromosomal sister taxa are interpreted to support an allopatric
rather than a stasipatric (chromosomal) means of speciation in all cases except one.
The shrews of the Sorex araneus group have undergone a spectacular chromosome evolution. The karyotype of Sorex granarius is generally considered ancestral to those of Sorex coronatus and S. araneus. However, a sequence of 777 base pairs of the cytochrome b gene of the mitochondrial DNA (mtDNA) produces a quite different picture: S. granarius is closely related to the populations of S. araneus from the Pyrenees and from the northwestern Alps, whereas S. coronatus and S. araneus from Italy and the southern Alps represent two well-separated lineages. It is suggested that mtDNA and chromosomal evolution are in this case largely independant processes. Whereas mtDNA haplotypes are closely linked to the geographical history of the populations, chromosomal mutations were probably transmitted from one population to another. Available data suggest that the impressive chromosome polymorphism of this group is quite a recent phenomenon.
Tiksi area in eastern Siberia has generally been believed to have remained ice-free throughout the entire Ice Age. However, new glacial geomorphological research in the region has revealed evidence of a former ice sheet centered on the East Siberian shelf and reaching as far as Tiksi Bay. Among indications supporting this concept are fresh-looking U-shaped valleys, giant flutes, rock drumlins and other ice-erosional features, as well as systems of glaciotectonic ridges coupled with rock basins ("hill-and-hole pairs")--all attesting to a former ice motion in a northeast-southwest direction. The work carried out in May 1990 by a Swedish-Soviet field party was aimed at resolving the chronology of the latest glacial events in the Tiksi area. To this end, the bottom sediments of two lakes joined by glaciotectonic ridges were cored, analysed and AMS-14C dated. The ages of 6450+/-110 6870+/-80 and 8500+/-160 radiocarbon years BP were minimum dates obtained for the beginning of lacustrine sedimentation in the basins. This suggested that the last icesheet glaciation of the area had been of Late Pleistocene age.
Substantiated cases of ring species in mammals are rare. I examined the variation in mitochondrial DNA (mtDNA) of Perognathus amplus and P. longimembris in and around Arizona to test the hypothesis proposed by Hoffmeister (1986) that these two taxa are members of a single ring species demonstrating circular overlap. Through digestion of purified mtDNA from 45 P. amplus and 35 P. longimembris with 16 type II restriction enzymes, I identified 38 distinct haplotypes that belong to eight different evolutionary lineages. I then amplified and directly sequenced a portion of the mitochondrial cytochrome-b region from individuals representative of the lineages identified by restriction fragments, and used these data for phylogeny reconstruction in both a parsimony and neighbor-joining setting. The resulting phylogeny was consistent with the ring hypothesis, but, based on the incompleteness of the ring of subspecies and the apparent timing of evolutionary events in this group, I conclude that P. amplus and P. longimembris are distinct lineages that have completed the speciation process.
Restriction fragment length polymorphism analysis of mitochondrial DNA (mtDNA) was used to examine the genetic structure among field voles (Microtus agrestis) from southern and central Sweden. A total of 57 haplotypes was identified in 158 voles from 60 localities. Overall mtDNA diversity was high, but both haplotype and nucleotide diversity exhibited pronounced geographic heterogeneity. Phylogenetic analyses revealed a shallow tree with seven primary mtDNA lineages separated by sequence divergences ranging from 0.6% to 1.0%. The geographic structure of mtDNA diversity and lineage distribution was complex but strongly structured and deviated significantly from an equilibrium situation. The extensive mtDNA diversity observed and the recent biogeographic history of the region suggests that the shallow mtDNA structure in the field vole cannot be explained solely by stochastic lineage sorting in situ or isolation by distance. Instead, the data suggest that the genetic imprints of historical demographic conditions and vicariant geographic events have been preserved and to a large extent determine the contemporary geographic distribution of mtDNA variation. A plausible historical scenario involves differentiation of mtDNA lineages in local populations in glacial refugia, a moving postglacial population structure, and bottlenecks and expansions of mtDNA lineages during the postglacial recolonization of Sweden. By combining the mtDNA data with an analysis of Y-chromosome variation, a specific population unit was identified in southwestern Sweden. This population, defined by a unique mtDNA lineage and fixation of a Y-chromosome variant, probably originated in a population bottleneck in southern Sweden about 12,000 to 13,000 calendar years ago.
A field vole (Microtus agrestis) population characterized by unique mitochondrial DNA (mtDNA) and Y chromosome markers occurs in southwest Sweden. A contact zone between this Lund (Lu) population and a standard (St) population was examined with two sex-specific genetic markers. The field vole mtDNA and Y chromosome clines display a remarkable lack of coincidence, rarely observed in contact zones. The cline width for both markers is about 50 km, but the two clines are displaced from each other: the mtDNA cline is found in the central part of the study area, whereas the cline for the Y chromosome is located in the eastern part. Thus, the absolute width of the Lu-St zone spans about 95-110 km. As a result of the cline shift, all male hybrids carry the Lu-Y chromosome and St-type mtDNA. The other possible male hybrid class is lacking. The distinct noncoincidence of the mtDNA and Y chromosome clines is most likely explained by selection against male hybrids with the St-Y chromosome and Lu-mtDNA. It is possible that incompatibilities between the maternal genome of Lu-type animals and the paternal genome of St-type individuals exist. However, alternative explanations based on neutrality or selective advantage cannot be totally dismissed.
The 17 modern Canadian arctic tundra mammals share only six broad patterns of taxonomic variation and geographic distribution. These are believed to result from differing distributions during the Wisconsin glacial stage, and the past distributions to have been in large part determined by the ecological relations of the species during the preceding interglacial stage. Those that were tundra species were able to maintain populations in the northern refugia, both in Beringia and Pearyland if the species was widespread (e.g., varying lemming) and only in the former if confined to western North America (e.g., brown lemming). Tree-line species (e.g., caribou) gave rise to both woodland and tundra forms, the former from populations isolated south of the ice, and the latter from populations trapped in the cooling northern refugia. Other species maintained themselves only in Beringia (e.g., man), and others only south of the ice-sheets (e.g., wolverine). Two species, polar bear and arctic fox, find sea-ice no barrier to distribution, and their present ranges are of as little zoogeographical relevance as those of anadromous fish.
1. Introduction 2. The species - what's in a name? 3. Speciation in allopatric populations 4. The founder effect 5. Chromosomal isolating mechanisms 6. The fixation of rearrangements 7. Fertility, viability and hybridity 8. Genic change and chromosomal speciation 9. Chromosomal speciation 10. Molecular mechanisms and speciation 11. Conclusions and perspectives References Index.
Past and recent changes in the position of the arctic tree line and spatial structure of nearby forests are reviewed. The advancing tree line in the arctic tundra in the first half of the Holocene was promoted by sexual regeneration because of warmer climate. The northernmost tree-line positions were reached in early Holocene in western North America and northern Eurasia, and during or after mid-Holocene in central and eastern North America. The position of the arctic tree line remained rather stable across the northern hemisphere from 3500 years BP to the present. General cooling during the late Holocene did not induce significant retreat of the tree line at sites not affected by catastrophic disturbances (fire) because trees and forests were able to survive through vegetative regeneration. Minor displacements deduced from dendroecological data were recorded during the last 500 years, whereas more important structural changes occurred in the nearby northernmost forests and tree groves through the shifting dominance of growth forms in preestablished tree and forest populations. The spatiotemporal pattern of tree-line and forest changes along the arctic border suggests that both equilibrium and nonequilibrium conditions prevailed during the Holocene.Key words: tree line, Arctic, climate change, paleoecology, Holocene.
In this paper, we present data on murid rodents obtained by three major techniques used in biochemical systematics today: protein electrophoresis, scnDNA hybridization and mtDNA RFLP. The data have been analysed by both phenetic and cladistic methods and results of the three techniques were compared with one another. Four clear major levels of divergence (or nodes) can be recognized by all methods. Node 1 groups four subspecies of M. musculus (domesticus, bactrianus, castaneus and musculus). Node 2 groups four species: M. musculus, M. spretus, M. spicilegus and M. spretoides. Node 3 groups the stem of node 2 and three strictly Oriental species (M. caroli, M. cervicolor and M. cookii) Node 4 groups the previous lineages with Oriental Pyromys and Coelomys and the Ethiopian Nannomys. However, the relationships within each level cannot be resolved without ambiguity. We argue that this is not due to the resolutive power of our methods, but to a biological reality, that is successive adaptive radiations marked by quasi-simultaneous speciation events linked with geographical colonization. Our estimation of divergence time between different taxa showed that the genus Mus is very young. The youngest ‘bona fide’ species are 1.1 Myr old, or even less than 0.3 Myr if one takes into consideration the two sibling species M. spicilegus and M. spretoides. It appears that mtDNA evolves three to six times faster than scnDNA. The zoogeographical history of the genus can be reconstructed as a séries of adaptative radiations leading to the present day distribution of the Palaearctic, Oriental, and Ethiopian groups of taxa.
The genetic effects of pleistocene ice ages are approached by deduction from paleoenvironmental information, by induction from the genetic structure of populations and species, and by their combination to infer likely consequences. (1) Recent palaeoclimatic information indicate rapid global reversals and changes in ranges of species which would involve elimination with spreading from the edge. Leading edge colonization during a rapid expansion would be leptokurtic and lead to homozygosity and spatial assortment of genomes. In Europe and North America, ice age contractions were into southern refugia, which would promote genome reorganization. (2) The present day genetic structure of species shows frequent geographic subdivision, with parapatric genomes, hybrid zones and suture zones. A survey of recent DNA phylogeographic information supports and extends earlier work. (3) The grasshopper Chorthippus parallelus is used to illustrate such data and processes. Its range in Europe is divided on DNA sequences into five parapatric races, with southern genomes showing greater haplotype diversity - probably due to southern mountain blocks acting as refugia and northern expansion reducing diversity. (4) Comparison with other recent studies shows a concordance of such phylogeographic data over pleistocene time scales. (5) The role that ice age range changes may have played in changing adaptations is explored, including the limits of range, rapid change in new invasions and refugial differentiation in a variety of organisms. (6) The effects of these events in causing divergence and speciation are explored using Chorthippus as a paradigm. Repeated contraction and expansion would accumulate genome differences and adaptations, protected from mixing by hybrid zones, and such a composite mode of speciation could apply to many organisms.
Lemmings of the genus Lemmus display a very moderate degree of karyotype diversity. In L. lemmus from the Kola Peninsula, L. sibiricus sibiricus from the Pechora inlet coast and the Laptev Sea coast, L.s. portenkoi from the Vrangell Island and L. amurensis from Southern Yakutia the gross chromosome morphology and C-banding pattern proved to be identical (2n = 50, NF = 50). The chromosome set of L.s. chrysogaster (the Chukotka Peninsula) consists of 23 pairs of acrocentrics and 2 pairs of subtelocentrics (2n = 50, NF = 54), and so it is identical to the karyotype of North American Lemmus. As to spatial structure of populations, population dynamics, degree of inbreeding and uniformity of habitats throughout the area, Lemmus is basically similar to the lemmings of another genus, Dicrostonyx. In the latter, however, an extensive chromosome diversity has been found. Therefore, the ecological and population characteristics mentioned above are suggested not to be essential for the rate of chromosome evolution in lemmings.
The details of mitochondrial DNA (mtDNA) phylogenetic structure of the northern grasshopper mouse Onychomys leucogaster were examined using populations from a postulated area of endemism that includes three arid regions (Colorado Plateaus, Interior Plains, and Wyoming Basins) in western North America. Fifteen tetra- and heptanucleotide restriction enzymes were used to assay restriction-site variation in a 2150-bp PCR-amplified fragment of mtDNA representing the ND2 and part of the COI gene regions. A total of 18 mtDNA haplotypes were detected. Although overall genetic divergence among these haplotypes was low (average = 1.1%), phylogeographic structuring was apparent. Notably, a clear phylogenetic split separated one group of haplotypes restricted to the Wyoming Basins from all others. This phylogenetic split was further corroborated by examination of nucleotide sequence variation from a 270-bp stretch of the mtDNA cytochrome b gene. Overall geographic and phylogenetic patterns suggest a complex history of geographic structuring and subsequent mixing of populations of grasshopper mice throughout the late Pleistocene. These patterns of variation are evaluated relative to alternative hypotheses about biotic responses to Quaternary climatic oscillations in western North American arid regions.
The population genetic structure of wood lemmings (Myopus schisticolor) from Scandinavia, Finland and western Siberia was examined by restriction fragment length polymorphism of mitochondrial DNA (mtDNA) in 45 individuals from six localities. The 12 observed mtDNA haplotypes demonstrated a distinct phylogeographic pattern, suggesting that the postglacial colonization of Scandinavia by wood lemmings occurred from north-east. However, a very low level of haplotype and nucleotide diversity and a lack of geographical structure were found within Scandinavia. The limited mtDNA diversity in the Scandinavian populations probably reflects recent divergence in situ after colonization by a limited number of founders. Allozyme data support this scenario.
The basic problem in reconstructing the last interglacial in the Siberian Arctic is to recognize correlative deposits in the Quaternary sequence. Assignment of any particular “warm” event to the last interglacial is usually based on various indirect Criteria. There is no one independent criterion that could distinguish the last interglacial from earlier or later warm periods. Potentially, the most rapidly evolved mammal lineage of collared lemmings could be helpful for dating the last interglacial in the Arctic, but there are still some problems to be solved. Another important problem is climatic interpretation of warm events presumably referred to the last interglacial. Most commonly such reconstructions are based on the concept of northward shift of modern-like plant communities. But some features of pollen spectra and insect faunas suggest a special character of communities existed during the warm events in the Arctic. They do not seem to be exact analogues of modern communities, and a non-uniformitarian approach is necessary for their climatic interpretation. Survival of tundra-steppe communities and grazing mammals through the last interglacial climatic change suggests that it was not so destructive for the Arctic ecosystems as the Pleistocene/Holocene environment restructuring.
Genetic variation in 114 woodrats (Neotoma) from 33 locations in the eastern and central United States was examined using analysis of mitochondrial DNA (mtDNA) restriction
sites. Results indicate that three major lineages of Neotoma floridana(southern, western, and northern) diverged in the early Pleistocene. The southern lineage exhibits substantial mtDNA variability
and population structure. The pattern of mtDNA variation in the southern lineage suggests that vicariance events, including
the insularization of Florida, have been important determinants of geographic variation. The low levels of sequence variation
within the northern and western lineages indicate that woodrat populations in these areas are probably the result of relatively
recent (Holocene) range expansions. These conclusions are not entirely consistent with the current taxonomy of eastern woodrats
and suggest that taxonomic revision is warranted.
Spectacular progress has been made recently in the study of evolution at the molecular level, primarily due to new biochemical techniques such as gene cloning and DNA sequencing. In this book, the author summarizes new developments and seeks to unify studies of evolutionary histories of organisms and the mechanisms of evolution into a single science - molecular evolutionary genetics.
Variation and change in mitochondrial DNA (mtDNA) is often assumed to conform to a constant mutation rate equilibrium neutral model of molecular evolution. Recent evidence, however, indicates that the assumptions underlying this model are frequently violated. The mitochondria) genome may be subject to the same suite of forces known to be acting in the nuclear genome, including hitchhiking and selection, as well as forces that do not affect nuclear variation. Wherever possible, evolutionary studies involving mtDNA should incorporate statistical tests to investigate the forces shaping sequence variation and evolution.
Comparison of mitochondrial DNA (mtDNA) control-region sequences of 155 dunlins from 15 breeding populations confirmed the existence of five major phylogeographic groups in the circumpolar breeding range of this migratory shorebird species. Time estimates of the origin of groups, based on sequence divergences and a molecular clock for birds, suggest a scenario of repeated fragmentation of populations in isolated tundra refugia during the late Pleistocene. The distribution of about three-quarters of all detected molecular variance between phylogeographic groups attests to the strongly subdivided genetic population structure in dunlins that is being maintained by natal philopatry. Each mtDNA phylogeographic group can be related to a morphometrically defined subspecies, but several other recognized subspecies are not supported by monophyletic mtDNA lineages within their purported ranges. More detailed analysis of several European populations reveals low amounts of gene flow and the partitioning of a substantial fraction of molecular variance between them. This ongoing evolution of population-genetic structuring within the European phylogeographic group most likely started with the last retreat of the ice sheets some 10,000 years ago. Dunlins thus provide one of the clearest examples of the linkage between historical and contemporary components of mtDNA phylogeographic structuring in birds.
The fascinating story of how a harsh terrain that resembled modern Antarctica has been transformed gradually into the forests, grasslands, and wetlands we know today. "One of the best scientific books published in the last ten years."âOttowa Journal "A valuable new synthesis of facts and ideas about climate, geography, and life during the past 20,000 years. More important, the book conveys an intimate appreciation of the rich variety of nature through time."âS. David Webb,Science
THE cause of extinction of the woolly mammoth, Mammuthus primigenius (Blumenbach), is still debated. A major environmental change at the Pleistocene-Holocene boundary, hunting by early man, or both together are among the main explanations that have been suggested. But hardly anyone has doubted that mammoths had become extinct everywhere by around 9,500 years before present (BP). We report here new discoveries on Wrangel Island in the Arctic Ocean that force this view to be revised. Along with normal-sized mammoth fossils dating to the end of the Pleistocene, numerous teeth of dwarf mammoth dated 7,000-4,000 yr BP have been found there. The island is thought to have become separated from the mainland by 12,000 yr BP. Survival of a mammoth population may be explained by local topography and climatic features, which permitted relictual preservation of communities of steppe plants. We interpret the dwarfing of the Wrangel mammoths as a result of the insularity effect, combined with a response to the general trend towards unfavourable environment in the Holocene.
A mathematical model for the evolutionary change of restriction sites in mitochondrial DNA is developed. Formulas based on this model are presented for estimating the number of nucleotide substitutions between two populations or species. To express the degree of polymorphism in a population at the nucleotide level, a measure called "nucleotide diversity" is proposed.
We consider the distribution of pairwise sequence differences of mitochondrial DNA or of other nonrecombining portions of the genome in a population that has been of constant size and in a population that has been growing in size exponentially for a long time. We show that, in a population of constant size, the sample distribution of pairwise differences will typically deviate substantially from the geometric distribution expected, because the history of coalescent events in a single sample of genes imposes a substantial correlation on pairwise differences. Consequently, a goodness-of-fit test of observed pairwise differences to the geometric distribution, which assumes that each pairwise comparison is independent, is not a valid test of the hypothesis that the genes were sampled from a panmictic population of constant size. In an exponentially growing population in which the product of the current population size and the growth rate is substantially larger than one, our analytical and simulation results show that most coalescent events occur relatively early and in a restricted range of times. Hence, the "gene tree" will be nearly a "star phylogeny" and the distribution of pairwise differences will be nearly a Poisson distribution. In that case, it is possible to estimate r, the population growth rate, if the mutation rate, mu, and current population size, N0, are assumed known. The estimate of r is the solution to ri/mu = ln(N0r) - gamma, where i is the average pairwise difference and gamma approximately 0.577 is Euler's constant.
A simple method is proposed for estimating the average number of nucleotide substitutions per site within and between populations for the case where a large number of individuals are examined for many restriction enzymes. This method gives essentially the same results as those obtained by Nei and Li's method but saves a large amount of computer time. The variances of the quantities estimated can be obtained by the jackknife method, and these variances are very similar to those obtained by Nei and Jin's more sophisticated method. A similar method can also be applied to DNA sequence data.
The relationship between the two estimates of genetic variation at the DNA level, namely the number of segregating sites and the average number of nucleotide differences estimated from pairwise comparison, is investigated. It is found that the correlation between these two estimates is large when the sample size is small, and decreases slowly as the sample size increases. Using the relationship obtained, a statistical method for testing the neutral mutation hypothesis is developed. This method needs only the data of DNA polymorphism, namely the genetic variation within population at the DNA level. A simple method of computer simulation, that was used in order to obtain the distribution of a new statistic developed, is also presented. Applying this statistical method to the five regions of DNA sequences in Drosophila melanogaster, it is found that large insertion/deletion (greater than 100 bp) is deleterious. It is suggested that the natural selection against large insertion/deletion is so weak that a large amount of variation is maintained in a population.
The expected number of segregating sites and the expectation of the average number of nucleotide differences among DNA sequences randomly sampled from a population, which is not in equilibrium, have been developed. The results obtained indicate that, in the case where the population size has changed drastically, the number of segregating sites is influenced by the size of the current population more strongly than is the average number of nucleotide differences, while the average number of nucleotide differences is affected by the size of the original population more severely than is the number of segregating sites. The results also indicate that the average number of nucleotide differences is affected by a population bottleneck more strongly than is the number of segregating sites.