Fine-scale population genetic structure and sex-biased dispersal in the smooth snake (Coronella austriaca) in southern England

Human-induced alteration of natural habitats has the potential to impact on the genetic structuring of remnant populations at multiple spatial scales. Species from higher trophic levels, such as snakes, are expected to be particularly susceptible to land-use changes. We examined fine-scale population structure and looked for evidence of sex-biased dispersal in smooth snakes (Coronella austriaca), sampled from 10 heathland localities situated within a managed coniferous forest in Dorset, United Kingdom. Despite the limited distances between heathland areas (maximum <6 km), there was a small but significant structuring of populations based on eight microsatellite loci. This followed an isolation-by-distance model using both straight line and 'biological' distances between sampling sites, suggesting C. austriaca's low vagility as the causal factor, rather than closed canopy conifer forest exerting an effect as a barrier to dispersal. Within population comparisons of male and female snakes showed evidence for sex-biased dispersal, with three of four analyses finding significantly higher dispersal in males than in females. We suggest that the fine-scale spatial genetic structuring and sex-biased dispersal have important implications for the conservation of C. austriaca, and highlight the value of heathland areas within commercial conifer plantations with regards to their future management.     

Biogeography of the smooth snake (Coronella austriaca): origin and conservation of the northernmost population

Understanding historical range expansions and population demography can be crucial for the conservation and management of endangered species. In doing so, valuable information can be obtained regarding, for example, the identification of isolated populations, associations to particular habitats and distribution range shifts. As poikilotherms, snakes are vulnerable to environmental changes that can greatly shape their distribution ranges. Here we used mitochondrial data to elucidate the origin of the smooth snake population in Åland island, which is the northernmost location where the species is found. In Åland, we used mitochondrial and microsatellite data to fine‐map its spatial genetic structure, infer its demographic dynamics and determine its effective population size. We found three independent lineages, which expanded north from Iberian, the Balkans and Caucasus regions. The central lineage originating in the Balkans was the only one that reached Scandinavia. The Åland population belongs to this lineage and potentially colonized the island from the west via Sweden. This population appeared to be critically small and fragmented into two genetically isolated subpopulations. We discuss our results in light of previous findings regarding colonization routes in Europe and Scandinavia. Moreover, we discuss the origin and current genetic status of the Åland population relative to other co‐occurring snakes and suggest conservation measures based on our findings. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 114 , 426–435.     

Polymorphic microsatellite markers,isolated using a simple enrichment procedure,in the threatened smooth snake (Coronella austriaca)

The smooth snake, Coronella austriaca, is particularly rare within the UK and little is known about the genetic variability within the species. Here we report the isolation of 16 polymorphic microsatellite markers in the smooth snake, using a simple enrichment procedure. Despite screening individuals from a potentially isolated population, levels of polymorphism were high. These microsatellite markers will prove very useful in investigating population parameters, which will lead to effective conservation and management plans for this rare species.     

Evaluating hypotheses on the origin and diversification of the ringneck snake Diadophis punctatus (Colubridae: Dipsadinae)

Close affinities recognized between taxa in Mexico and the contiguous USA have led to a variety of biogeographical scenarios. One such hypothesis suggests that species that occur in both countries have an origin in central Mexico followed by dispersal into the USA. This study expands upon previous phylogeographical work of the ringneck snake Diadophis punctatus by incorporating new data from previously unsampled areas appropriate to critically assess hypotheses regarding a Mexican origin for this species. Maximum likelihood and maximum parsimony analyses inferred a derived position for the lineage from southern Mexico with constraint tests for alternate evolutionary hypotheses resulting in significantly worse likelihood values. Ancestral area reconstructions inferred an origin for D. punctatus in the south‐eastern USA followed by a south‐east to north‐east then westward directionality of historical migration. The position within the phylogeny and date estimate for the south‐western + Mexico clade suggests a recent invasion into central Mexico with expansion into the Nearctic/Neotropic transition zone. The extensive lineage diversity inferred from the mtDNA suggests that the genus is a complex of cryptic species whose conservational status should be re‐evaluated on both the national and regional levels. © 2009 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 158 , 629–640.     

Reduced genetic variation and strong genetic population structure in the freshwater killifish Valencia letourneuxi (Valenciidae) based on nuclear and mitochondrial markers

The genetic variation of the critically endangered Corfu killifish (Valencia letourneuxi), an endemic freshwater fish species of the western Balkans, was assessed for nine populations sampled in eight water systems in western continental Greece, the Peloponnese and the Ionian Island of Corfu, using mitochondrial and microsatellite markers. The analyses were based on data from three mtDNA regions (D‐loop, COI and 16S rRNA sequences) and 14 microsatellite loci. Samples from the congeneric species Valencia hispanica and the phylogenetically closely related species Aphanius fasciatus were also used in the study as outgroups. Both the mitochondrial and the microsatellite analyses revealed three distinct population groupings associated with the geographical distribution of the populations: one southern group occupying rivers draining to the Patraikos Gulf, the second one including the populations flowing into the Amvrakikos Gulf and the third, more northern group, including the other populations from rivers in Corfu Island and Epirus flowing into the Ionian Sea. Within these groupings there is limited genetic differentiation between populations; in addition, there is reduced intrapopulation genetic variation, evidenced by low heterozygosity values, number of alleles and haplotype diversity. In terms of taxonomic implications and appropriate management actions for conservation, our data suggest that the major population groups should be regarded at least as three distinct conservation units (CUs), with translocation and restocking actions to take place only within the geographical range of the CU concerned. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 334–349.     

Phylogeography of the Temminck’s Stint (Calidris temminckii): historical vicariance but little present genetic structure in a regionally endangered Palearctic wader

Aim We study the population differentiation and phylogeography of the Temminck’s Stint (Calidris temminckii). Specifically, we seek signs of past and present population size changes and dispersal events and evaluate management and conservation unit status of the populations. We also study the possibility of introgression as the origin of two mitochondrial DNA (mtDNA) lineages found and estimate the divergence time of the lineages. Location Northern Eurasia. Methods We analysed 583 bp of mtDNA control region domains I and II and 11 microsatellite loci from 13 localities throughout the breeding range. In addition, we used mitochondrial cytochrome c oxidase subunit I (COI), a barcoding gene, to search for signs of introgression. Results More population differentiation was found from microsatellites than from mtDNA, although differentiation was weak in both markers. Signs of past population growth were observed, in addition to more recent decline in some areas. Both control region and COI sequences revealed two maternal lineages coexisting in Fennoscandia and in north‐west Siberia. No signs of introgression were detected. Lineage divergence time was estimated to have occurred during the glacial periods of Pleistocene. Main conclusions Slight differences in mtDNA and microsatellite differentiation and diversity may reflect different features – such as the mutation rate and effective population size – of the markers used, or female‐biased dispersal pattern and high male site‐fidelity of the species. The coexistence of the two mitochondrial lineages is most likely a consequence of post‐glacial mixing of two refugial Pleistocene populations. Based on genetic information alone, global conservation concerns are not imminent. However, fast decline of a marginal Bothnian Bay population and the smallness and remoteness of a Central Yakutian population warrant conservation actions.     

Evolution and phylogeny of the genus Natrix (Serpentes: Colubridae)

Some aspects of the natural history of snakes of the colubrid genus Natrix have been well studied. With their extensive European distribution and relative abundance, their ecology, reproduction and behaviour are well known. Yet other facets of their biology remain poorly understood. These include knowledge of Natrix phylogeny, hypotheses explaining the current distribution of the three extant members of the genus, and their evolution and relationships. In this study we used molecular data, the nucleotide sequences of four protein-coding mitochondrial genes (3806 bp total), to provide a well-supported phylogeny for the genus Natrix . With these molecular data, evidence from the fossil record, and knowledge of palaeogeological events, we used two approaches in designing a time scale which we used to date the major events in Natrix speciation and intraspecific variation. Our data strongly support a phylogeny for the genus in which N. maura is basal with N. natrix and N. tessellata being sister species. The calibrated molecular clock suggests that N. maura diverged from the common ancestor of the three species 18–27 mya and that N. natrix and N. tessellata diverged 13–22 mya. Although the ranges of these estimates are large they support an early Miocene to late Oligocene origin for the three species. Intraspecific divergence is estimated to have commenced 5.3, 6.0 and 6.7 mya with evolutionary rates of 1 : 1.25 : 1.35% per million years for N. maura, N. natrix and N. tessellata , respectively.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 87 , 127–143.     

Evolution of coloration, urotomy and coral snake mimicry in the snake genus Scaphiodontophis (Serpentes: Colubridae)

The Neotropical hinged-tooth, coral snake mimics of the genus Scaphiodontophis are characterized by extremely long and disproportionately thick tails that are extremely fragile. Both the coloration and tail structure are putative antipredator devices. While all examples have components of the coloration that match those of the venomous coral snakes (family Elapidae), the range of variation is extreme, leading to controversy on the status of various populations, including nine named taxa. Individual, ontogenetic and geographic variation in scutellation and head, body and tail coloration were analysed to evaluate population status and possible evolutionary trends based on a sample of 183 examples from Mexico, Central America and Colombia. Variation in subcaudal counts show population differences (higher in Mexico and upper Central America) but are not congruent with geographic variation in coloration. Generally snakes from north of Nicaragua and from central and eastern Panama have a pattern of dyads (black-light-black bands separating red bands), those from Atlantic slope Nicaragua to western Panama a pattern of monads (light-black-light bands separating the red ones) and those from Colombia have both pattern types on the same snake. The dyads and/or monads may be present the length of the body and tail, restricted to the anterior part of the body or on the entire body or on the anterior part of the body and on the tail. Two or more of these variants may occur at a single geographic locality or only a single one may be present. Head and nuchal colour patterns (Z, A, V and Du) are relatively consistent geographically. The Adantic slope Guatemala, Belize and Honduras population have the A pattern, those of Nicaragua, Costa Rica and western Panama the V pattern, and those in Colombia a Du pattern. Other populations have the Z coloration. Intermediate conditions in coloration of the body and tail and head and neck are found at localities intermediate between the main pattern types, indicating intergradation among adjacent populations. Consequently, we regard these snakes as representative of a single species, Scaphiodontophis annulatus Dumeril and Bibron and the eight other names applied to various populations and individuals as synonyms. Analysis of colour pattern leads us to the conclusion that the tricolour pattern evolved from a uniform one through a lineate-spotted condition (usually present on the non-tricolour portions of the snake) through a bicolour red and black pattern to the dyadal condition. The monadal pattern in turn was derived from the dyadal one. The data further indicates that tricolour components first appeared anteriorly and progressively expanded posteriorly. The evolutionary sequence for the head and nuchal pattern appears to be A → Z → V → Du S. annulatus has a series of jaw and tooth specializations designed for rapid processing of hard-bodied prey found during diurnal foraging in the leaf-litter. Urotomy in this species involves intervertebral tail-breakage (pseudoautotomy) without regeneration. Evidence is presented supporting the long-tail multiple break hypothesis as applicable to Scaphiodontophis and other snakes with similar tail morphology (specialized pseudoautotomy). This is in contrast to snakes with similar tail morphology (specialized pseudoautotomy). This is in contrast to Coniophanes and other snakes with a high incidence of urotomy having long but unspecialized tails (unspecialized pseudoautotomy) without multiple breaks over time. All Scaphiodontophis colour patterns have a general resemblance to that of venomous coral snakes and offer protection from generalizing predators having innate or other triggered responses to coral snake colours. The aposematic effect is enhanced by tail thrashing and head twitching behaviours. The characteristic foraging pose of S. annulatus, which tends to expose the head and anterior body, makes even the incomplete tricolour pattern effective as an antipredator defence. No evidence supports the idea that tail thrashing or the incomplete tricolour pattern directs the predator attacks to the tail to expedite pseudoautotomy. Coral snake mimicry and specialized pseudoautotomy are shown not to be co-evolved and pseudautotomy seems to have evolved long before mimetic coloration in this genus.     

Multilocus phylogeography of the European ground squirrel: cryptic interglacial refugia of continental climate in Europe

The theory of classical and cryptic Pleistocene refugia is based mainly on historical changes in temperature, and the refugia are usually defined within a latitudinal gradient. However, the gradient of oceanic–continental climate (i.e. longitudinal) was also significantly variable during glacial cycles with important biotic consequences. Range‐wide phylogeography of the European ground squirrel (EGS) was used to interpret the evolutionary and palaeogeographical history of the species in Europe and to shed light on its glacial–interglacial dynamic. The EGS is a steppe‐inhabiting species and the westernmost member of the genus in the Palaearctic region. We have analysed 915 specimens throughout the present natural range by employing mitochondrial DNA sequences (cytochrome b gene) and 12 nuclear microsatellite markers. The reconstructed phylogeography divides the species into two main geographical groups, with deep substructuring within both groups. Bulgaria is the centre of the ancestral area, and it also has the highest genetic diversity within the species. The northernmost group of the EGS survived in the southern part of Pannonia throughout several glacial–interglacial cycles. Animals from this population probably repeatedly colonized areas further to the north and west during the glacial periods, while in the interglacial periods, the EGS distribution contracted back to this Pannonian refugium. The EGS thus represents a species with a glacial expansion/interglacial contraction palaeogeographical dynamics, and the Pannonian and southeastern Balkanian steppes are supported as cryptic refugia of continental climate during Pleistocene interglacials.     

Field observations of mating behavior in the neck-banded snake Scaphiodontophis annulatus (Serpentes: Colubridae)

We observed the mating behavior of the neck-banded snake Scaphiodontophis annulatus (a common species of colubrid in the South Pacific of Costa Rica) in the pre-montane wet forest of Las Cruces Biological Station (San Vito de Java, Costa Rica). Three S. annulatus were observed during courtship between 10-12 AM in a patch of primary forest. The two males were observed to interact with the female, but not signs of male-male agonistic interactions were observed. Their behavior includes grabbing and holding the female, copula, and biting during the copula.     

Extensive genetic divergence in the East Asian natricine snake,Rhabdophis tigrinus (Serpentes: Colubridae), with special reference to prominent geographical differentiation of the mitochondrial cytochrome b gene in Japanese populations

We investigated intraspecific phylogenetic relationships in the natricine snake, Rhabdophis tigrinus. A partial sequence of mitochondrial cytochrome b gene (990 bp) was sequenced for 220 individuals from 112 populations. The phylogeny indicated monophyly of the Japanese populations against the continental and Taiwanese populations, sister relationships of the Japanese and continental populations, and monophyly of the whole species. The results strongly suggested substantial genetic divergences among population assemblages from those three regions. We thus consider both lateralis from the continent, which is often synonymized to R. tigrinus, and formosanus from Taiwan, which is usually regarded as a subspecies of the latter, as distinct full species based on the evolutionary species concept. In the Japanese populations, haplotypes were classified to in two major clades (I and II) that were parapatric to each other. Clade I consisted of three distinct subclades (I‐A, I‐B, and I‐C), of which the former two were parapatric with each other, whereas the latter was sympatric with each of the former two subclades. The geographical haplotype structure exhibited by the Japanese populations is likely to have resulted from a series of allopatric differentiations with rapid range extensions of resultant lineages, leading to secondary contact or further admixture of mitochondrial haplotype clades and subclades. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 395–408.     

Nuclear DNA microsatellite analysis of genetic diversity and gene flow in the Scandinavian brown bear (Ursus arctos)

In the 1930s, the Scandinavian brown bear was close to extinction due to vigorous extermination programmes in Norway and Sweden. Increased protection of the brown bear in Scandinavia has resulted in the recovery of four subpopulations, which currently contain close to 1000 individuals. Effective conservation and management of the Scandinavian brown bear requires knowledge of the current levels of genetic diversity and gene flow among the four subpopulations. Earlier studies of mitochondrial DNA (mtDNA) diversity revealed extremely low levels of genetic variation, and population structure that grouped the three northern subpopulations in one genetic clade and the southernmost subpopulation in a second highly divergent clade. In this study, we extended the analysis of genetic diversity and gene flow in the Scandinavian brown bear using data from 19 nuclear DNA microsatellite loci. Results from the nuclear loci were strikingly different than the mtDNA results. Genetic diversity levels in the four subpopulations were equivalent to diversity levels in nonbottlenecked populations from North America, and significantly higher than levels in other bottlenecked and isolated brown bear populations. Gene flow levels between subpopulations ranged from low to moderate and were correlated with geographical distance. The substantial difference in results obtained using mtDNA and nuclear DNA markers stresses the importance of collecting data from both types of genetic markers before interpreting data and making recommendations for the conservation and management of natural populations. Based on the results from the mtDNA and nuclear DNA data sets, we propose one evolutionarily significant unit and four management units for the brown bear in Scandinavia.     

Phylogeography of lemmings (Lemmus): no evidence for postglacial colonization of Arctic from the Beringian refugium

Beringia is considered as an important glacial refugium that served as the main source for colonization of formerly glaciated Arctic regions. To obtain high resolution views of Arctic refugial history, we examined mitochondrial cytochrome b phylogeography in the northern genus of rodents, Lemmus (true lemmings), sampled across its circumpolar distribution. Strong phylogeographical structure suggests vicariant separation over several glacial-interglacial periods and does not provide evidence supporting the importance of Beringia for extensive colonization of formerly glaciated regions. Rather than a source of postglacial colonization, Beringia represents an area of intraspecific endemism previously undetected by biogeographical analysis. Existing phylogeographical structure suggests that vicariant separation by glacial barriers was an important factor generating genetic divergence and, thus, increasing genetic diversity in lemmings on continental and circumpolar scales. However, there is little evidence for the direct effect of the last glaciation on the level of genetic variation and allele genealogy in lemmings on a regional geographical scale. This finding implies that the population genetic models of postglacial colonization suggested for temperate taxa might have limited applicability for Arctic species.     

The population genetic structure of a large temperate pollinator species, Bombus pascuorum (Scopoli) (Hymenoptera: Apidae)

The genetic population structure of the bumble bee Bombus pascuorum was studied using six microsatellite loci and a partial sequence of the mitochondrial gene cytochrome b . Eighteen populations from central and northern Europe were included in the analysis. Observed levels of genetic variability and heterozygosity were high. Estimates of population differentiation based on F - and Φ-statistics revealed significant genetic differentiation among B. pascuorum populations and suggest that two partially isolated gene pools, separated by the Alps, do exist. The distribution of mtDNA haplotypes supports this view and presents direct evidence for gene flow across the Alps. Estimates of the number of migrants exchanged among populations north of the Alps suggest that historical events may have left a strong imprint on population structure.     

Mitochondrial and nuclear DNA phylogeography of European grayling (Thymallus thymallus): evidence for secondary contact zones in central Europe

Mitochondrial and microsatellite DNA markers were applied to infer the phylogeography, intraspecific diversity and dynamics of the distributional history of European grayling (Thymallus thymallus) with focus on its central and northern European distribution range. Phylogenetic and nested clade analyses revealed at least four major mtDNA lineages, which evolved in geographical isolation during the Pleistocene. These lineages should be recognized as the basic evolutionary significant units (ESUs) for grayling in central and northern Europe. In addition, and in contrast to previous work on grayling, the results of Bayesian analysis of individual admixture coefficients, two-dimensional scaling analysis and spatial analysis of molecular variance provided evidence for a high level of admixture among major lineages in contact zones between drainages (e.g. the low mountain range of Germany), most likely resulting from glacial perturbations and ancient river connections between drainages during the Pleistocene glaciations. Even within river systems, a high level of differentiation among populations was revealed as indicated by the microsatellite data. Grayling sampled from 29 sites displayed high levels of differentiation (overall F(ST) = 0.367), a high number of private alleles and high bootstrap support for the genetic distance-based population clusters across 12 loci. We specifically discuss our results in context of phylogeograpic studies on other European freshwater fish species with habitat preferences similar to those of grayling. Our study shows that both large-scale phylogeographical and detailed genetic analyses on a fine scale are mandatory for developing appropriate conservation guidelines of endangered species.     

Phylogeography and alpha taxonomy of the common dolphin (Delphinus sp.)

The resolution of taxonomic classifications for delphinid cetaceans has been problematic, especially for species in the genera Delphinus, Tursiops and Stenella. The frequent lack of correspondence between morphological and genetic differentiation in these species raises questions about the mechanisms responsible for their evolution. In this study we focus on the genus Delphinus, and use molecular markers to address questions about speciation and the evolution of population structure. Delphinus species have a worldwide distribution and show a high degree of morphological variation. Two distinct morphotypes, long-beaked and short-beaked, have been considered different species named D. capensis and D. delphis, respectively. However, genetic differentiation between these two forms has only been demonstrated in the Pacific. We analysed samples from eight different geographical regions, including two morphologically defined long-beaked form populations, and compared these with the eastern North Pacific populations. We found high differentiation among the populations described as long-beaked instead of the expected monophyly, suggesting that these populations may have evolved from independent events converging on the same morphotype. We observed low genetic differentiation among the short-beaked populations across a large geographical scale. We interpret these phylogeographical patterns in the context of life history and population structure in related species.     

Distribution and genetic divergence of two parapatric sibling ant species in Central Europe

The two sibling ant species Temnothorax nylanderi and Temnothorax crassispinus are widely distributed throughout deciduous forests in Europe. Their resemblance in morphology and similar ecological requirements suggest that they evolved from the same ancestral species in different glacial refugia and re-immigrated into Central Europe after the last ice age. Here, we show that the two species are parapatrically distributed in south-eastern Germany and hybridize along a narrow contact zone close to the continental divide. Phylogeographical data based on the mitochondrial genes cytochrome oxidase subunit I and cytochrome b suggest that the dominant haplotypes for T. nylanderi and T. crassispinus might have diverged already 1.5–2 Mya. Intraspecific variability is extremely low in both species, which might be explained by severe bottlenecks during rapid postglacial expansion into Central Europe.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 88 , 223–234.     

Phylogeography, hybridization and Pleistocene refugia of the kob antelope (Kobus kob)

Mitochondrial DNA control region sequences and seven microsatellites were used to estimate the genetic structuring, evolutionary history and historic migration patterns of the kob antelope (Kobus kob). Ten populations were analysed, representing the three recognized K. kob subspecies: K. k. kob in west Africa, K. k. thomasi in Uganda and K. k. leucotis in Sudan and Ethiopia. Despite being classified as K. k. thomasi and being phenotypically identical to the kob in Queen Elizabeth National Park (NP), the Murchison Falls population in Uganda showed high genetic similarity with the phenotypically distinct K. k. leucotis populations in Sudan and Ethiopia. This was regardless of marker type. Pairwise comparisons and genetic distances between populations grouped Murchison with K. k. leucotis, as did the Bayesian analysis, which failed to find any genetic structuring within the group. We propose that the divergent phenotype and life-history adaptations of K. k. leucotis reflect the isolation of kob populations in refugia in west and east Africa during the Pleistocene. Subsequent dispersal has led to secondary contact and hybridization in northern Uganda between lineages, which was supported by high levels of genetic diversity in Murchison. The reduced variability observed in Queen Elizabeth NP reflects a small founder population from west Africa and in part the decimation of Uganda's wildlife during the country's political turmoil in the 1970s. Due to similarities in phenotype and ecology, and the joint evolutionary history of their mtDNA sequences, the taxonomic status of K. k. kob and K. k. thomasi as separate subspecies is called into question.     

Phylogeography across a continent: the evolutionary and demographic history of the North American racer (Serpentes: Colubridae: Coluber constrictor)

Most phylogeographic studies examine organisms that do not have transcontinental distributions and therefore the genetic and temporal effects of barriers across an entire continent cannot be assessed with respect to a single species. We examined the phylogeographic structure, lineage age, and historical demography using sequences from the mtDNA cytochrome b gene of the widespread North American racer (Coluber constrictor), one of the few abundant transcontinental snakes that occurs throughout many diverse biomes. Our results indicate that this complex is comprised of six lineages differing greatly in geographic extent, with the largest (a central US clade) being approximately 26 times greater than the smallest (a lineage restricted to the Florida Panhandle and nearby portions of adjacent States). Most of the six lineages appear to be separated at previously identified genetic barriers for several vertebrates with similar ranges. Lineage diversification in this species began in the late Miocene, separating populations in the Florida Peninsula from the remainder of the US. Diversification of lineages continued throughout the Pliocene and early Pleistocene. Four of the six lineages occur east of the Mississippi River, with only two distinctly young ( approximately 1.5 mya) lineages found west of the Mississippi River (one occurs west of Continental Divide). All methods of demographic inference, including the mismatch distribution, Fu and Li's D and Tajima's D , and Bayesian skyline plots revealed population expansion occurring in the mid-to-late Pleistocene for every lineage, regardless of size or proximity to formerly glaciated areas. Population expansion for lineages found east of the Mississippi River occurred earlier and was much greater than those found west of the River.