Phylogeography of a high‐dispersal New Zealand sea‐star: does upwelling block gene‐flow?

New Zealand's (NZ) geographical isolation, extensive coastline and well-characterized oceanography offer a valuable system for marine biogeographical research. Here we use mtDNA control region sequences in the abundant endemic sea-star Patiriella regularis to test the following literature-based predictions: that coastal upwelling disrupts north-south gene flow and promotes population differentiation (hypothesis 1); and that an invasive Tasmanian population of the species was introduced anthropogenically from southern New Zealand (hypothesis 2). We sequenced 114 samples from 22 geographical locations, including nine sites from North Island, nine from South Island, one from Stewart Island and three from Tasmania. Our analysis of these sequences revealed an abundance of shallow phylogenetic lineages within P. regularis (68 haplotypes, mean divergence 0.9%). We detected significant genetic heterogeneity between pooled samples from northern vs. southern New Zealand (FST = 0.072; P = 0.0002), consistent with the hypothesis that upwelling disrupts gene flow between these regions (hypothesis 1). However, we are currently unable to rule out the alternative hypothesis that Cook Strait represents a barrier to dispersal (North Island vs. South Island; FST = 0.031; P = 0.0467). The detection of significant spatial structure in NZ samples is consistent with restricted gene flow, and the strong structure evident in northern NZ may be facilitated by distinct ocean current systems. Four shared haplotypes and nonsignificant differentiation (FST = 0.025; P = 0.2525) between southern New Zealand and Tasmanian samples is consistent with an anthropogenic origin for the latter population (hypothesis 2).     

Glacial refugia in a maritime temperate climate: Cicada (Kikihia subalpina) mtDNA phylogeography in New Zealand

Understanding the biological significance of Pleistocene glaciations requires knowledge of the nature and extent of habitat refugia during glacial maxima. An opportunity to examine evidence of glacial forest refugia in a maritime, Southern Hemisphere setting is found in New Zealand, where the extent of Pleistocene forests remains controversial. We used the mitochondrial phylogeography of a forest-edge cicada ( Kikihia subalpina ) to test the hypothesis that populations of this species survived throughout South Island during the Last Glacial Maximum. We also compared mitochondrial DNA phylogeographic patterns with male song patterns that suggest allopatric divergence across Cook Strait. Cytochrome oxidase I and II sequences were analyzed using network analysis, maximum-likelihood phylogenetic estimation, Bayesian dating and Bayesian skyline plots. K. subalpina haplotypes from North Island and South Island form monophyletic clades that are concordant with song patterns. Song divergence corresponds to approximately 2% genetic divergence, and Bayesian dating suggests that the North Island and South Island population-lineages became isolated around 761 000 years bp . Almost all South Island genetic variation is found in the north of the island, consistent with refugia in Marlborough Sounds, central Nelson and northwest Nelson. All central and southern South Island and Stewart Island haplotypes are extremely similar to northern South Island haplotypes, a 'northern richness/southern purity' pattern that mirrors genetic patterns observed in many Northern Hemisphere taxa. Proposed southern South Island forest habitat fragments may have been too small to sustain populations of K. subalpina , and/or they may have harboured ecological communities with no modern-day analogues.     

Genetic structure of desert ground squirrels over a 20-degree-latitude transect from Oregon through the Baja California peninsula

The genetic structure of populations over a wide geographical area should reflect the demographic and evolutionary processes that have shaped a species across its range. We examined the population genetic structure of antelope ground squirrels (Ammospermophilus leucurus) across the complex of North American deserts from the Great Basin of Oregon to the cape region of the Baja California peninsula. We sampled 73 individuals from 13 major localities over this 2500-km transect, from 43 to 22 degrees north. Our molecular phylogeographical analysis of 555 bp of the mitochondrial cytochrome b gene and 510 bp of the control region revealed great genetic uniformity in a single clade that extends from Oregon to central Baja California. A second distinct clade occupies the southern half of the peninsula. The minimal geographical structure of the northern clade, its low haplotype diversity and the distribution of pairwise differences between haplotypes suggest a rapid northward expansion of the population that must have followed a northward desert habitat shift associated with the most recent Quaternary climate warming and glacial retreat. The higher haplotype diversity within the southern clade and distribution of pairwise differences between haplotypes suggest that the southern clade has a longer, more stable history associated with a southern peninsular refugium. This system, as observed, reflects both historical and contemporary ecological and evolutionary responses to physical environmental gradients within genetically homogeneous populations.     

Pleistocene refugia in an arid landscape: analysis of a widely distributed Australian passerine

While many studies have documented the effect that glacial cycles have had on northern hemisphere species, few have attempted to study the associated effect of aridification at low latitudes in the southern hemisphere. We investigated the past effects that cyclic aridification may have had on the population structure and history of a widespread endemic Australian bird species, the Australian magpie (Gymnorhina tibicen). One thousand one hundred and sixty-six samples from across its native range were analysed for mitochondrial control region sequence variation and variation at six microsatellite loci. Analysis of mitochondrial control region sequence data indicated monophyletic clades that were geographically congruent with an eastern and western region. The contemporary distribution of east and west clades is nonoverlapping but in close proximity. Populations were estimated to have diverged in the Pleistocene around 36,000 years ago. The putative Carpentarian and Nullarbor arid barriers appear to be associated with the divergence between east and west mainland populations. Nested clade analysis indicated a signature of range expansion in the eastern region suggesting movement possibly inland and northward subsequent to the last period of aridity. The island population of Tasmania was of very recent origin, possibly since sea levels rose 16,000 years ago. Given the east-west structure, there was no congruence between morphology and recent history of this species indicating a lack of support for morphological taxa. Overall mitochondrial DNA and microsatellite variation suggest that increasing aridity and Pleistocene refugia played a role in structuring populations of the Australian magpie; however, the dispersal ability and generalist habitat requirements may have facilitated the movement of magpies into an almost contiguous modern distribution across the continent. This study supports the idea that Pleistocene aridification played an important role in structuring intraspecific variation in low latitudinal southern hemisphere avian species.     

Mitochondrial evidence for panmixia despite perceived barriers to gene flow in a widely distributed waterbird

We examined the mitochondrial genetic structure of American white pelicans (Pelecanus erythrorhynchos) to: 1) verify or refute whether American white pelicans are panmictic and 2) understand if any lack of genetic structure is the result of contemporary processes or historical phenomena. Sequence analysis of mitochondrial DNA control region haplotypes of 367 individuals from 19 colonies located across their North American range revealed a lack of population genetic or phylogeographic structure. This lack of structure was unexpected because: 1) Major geographic barriers such as the North American Continental Divide are thought to limit dispersal; 2) Differences in migratory behavior are expected to promote population differentiation; and 3) Many widespread North American migratory bird species show historic patterns of differentiation resulting from having inhabited multiple glacial refugia. Further, high haplotype diversity and many rare haplotypes are maintained across the species' distribution, despite frequent local extinctions and recolonizations that are expected to decrease diversity. Our findings suggest that American white pelicans have a high effective population size and low natal philopatry. We suggest that the rangewide panmixia we observed in American white pelicans is due to high historical and contemporary gene flow, enabled by high mobility and a lack of effective physical or behavioral barriers.     

Phylogeography of Silver Pheasant (Lophura nycthemera L.) across China: aggregate effects of refugia,introgression and riverine barriers

The role of Pleistocene glacial cycles in forming the contemporary genetic structure of organisms has been well studied in China with a particular focus on the Tibetan Plateau. However, China has a complex topography and diversity of local climates, and how glacial cycles may have shaped the subtropical and tropical biota of the region remains mostly unaddressed. To investigate the factors that affected the phylogeography and population history of a widely distributed and nondeciduous forest species, we analysed morphological characters, mitochondrial DNA sequences and nuclear microsatellite loci in the Silver Pheasant (Lophura nycthemera). In a pattern generally consistent with phenotypic clusters, but not nominal subspecies, deeply divergent mitochondrial lineages restricted to different geographic regions were detected. Coalescent simulations indicated that the time of main divergence events corresponded to major glacial periods in the Pleistocene and gene flow was only partially lowered by drainage barriers between some populations. Intraspecific cytonuclear discordance was revealed in mitochondrial lineages from Hainan Island and the Sichuan Basin with evidence of nuclear gene flow from neighbouring populations into the latter. Unexpectedly, hybridization was revealed in Yingjiang between the Silver Pheasant and Kalij Pheasant (Lophura leucomelanos) with wide genetic introgression at both the mtDNA and nuclear levels. Our results highlight a novel phylogeographic pattern in a subtropical area generated from the combined effects of climate oscillation, partial drainage barriers and interspecific hybridization. Cytonuclear discordance combined with morphological differentiation implies that complex historical factors shaped the divergence process in this biodiversity hot spot area of southern China.     

Historical biogeography and post-glacial recolonization of South American temperate rain forest by the relictual marsupial Dromiciops gliroides

Aim Long‐term climatic variation has generated historical expansions and contractions of species ranges, with accompanying fragmentation and population bottlenecks, which are evidenced by spatial variation in genetic structure of populations. We examine here hypotheses concerning dispersal and vicariance in response to historical geoclimatic change and potential isolation produced by mountains and water barriers. Location The temperate rain forest of southern South America, which is distributed from coastal Chile, including the large continental island of Chiloé, across the Andes into Argentina. Methods We investigated our hypotheses in the phylogenetically and biogeographically relictual marsupial Dromiciops gliroides. We examined 56 specimens, which resulted from field samples and museum study skins from 21 localities. We evaluated the influence of two major barriers, the Andean cordillera and the waterway between the mainland and the large island of Chiloé, by performing Bayesian and maximum‐likelihood phylogenetic analyses on sequences of 877 base pairs of mitochondrial DNA. We further tested the contribution of the proposed geographical barriers using analysis of molecular variance (amova ). We also evaluated the responses of populations to historical north–south shifts of habitat associated with glacial history and sea‐level change. Results Our analyses revealed a phylogeny with three clades, two of which are widespread and contain nearly all the haplotypes: a northern clade (36–39° S) and a southern clade (40–43° S). These two clades contain forms from both sides of the Andes. Within the southern clade, island and mainland forms were not significantly differentiated. Tests of recent demographic change revealed that southern populations have experienced recent expansion, whereas northern populations exhibit long‐term stability. The direction of recent gene flow and range expansion is predominantly from Chile to Argentina, with a modest reciprocal exchange across the Andes. Recent gene flow from the island of Chiloé to the mainland is also supported. Main conclusions The genetic structure of contemporary D. gliroides populations suggests recent gene flow across the Andes and between the mainland and the island of Chiloé. Differences in demographic history that we detected between northern and southern populations have resulted from historical southward shifts of habitat associated with glacial recession in South America. Our results add to a growing literature that demonstrates the value of genetic data to illuminate how environmental history shapes species range and population structure.     

Chloroplast sharing in the Tasmanian eucalypts

The biogeographic pattern of chloroplast DNA (cpDNA) haplotypes in Eucalyptus on the island of Tasmania is consistent with reticulate evolution, involving at least 12 Tasmanian species from the subgenus Symphyomyrtus. Intraspecific cpDNA polymorphism in 14 of 17 species is coupled with extensive sharing of identical haplotypes across populations of different species in the same geographic area. Haplotype diversity is lowest in central regions of Tasmania formerly occupied by alpine vegetation during glacial intervals and in northern regions that were periodically linked to continental Australia by land bridges. The observed distribution of several cpDNA haplotypes unique to Tasmania coincides with modeled locations of glacial refugia in coastal areas of Tasmania and shows the power of cpDNA in unraveling the complex history of past distributions of Eucalyptus. The results suggest that the model of evolution of the eucalypts should be reassessed to allow for the anastomosing effects of interspecific hybridization and introgression.     

Reconciling historical processes and population structure in the sooty tern Sterna fuscata

To test the influence of past vicariant events on population genetic structure of the sooty tern Sterna fuscata , we examined sequence variation in the mitochondrial control region of individuals from the Indo-Pacific and Atlantic Oceans. Our analyses indicate a rapid population expansion at a global scale during the last 100 000 years, consistent with global recolonisation during the interstade following the Pleistocene glacial maxima (125 000–175 000 years bp). We estimate islands of the Great Barrier Reef and Coral Sea were colonised no more than 16 000 years ago, most likely in association with the appearance of new breeding habitat following the final Pleistocene glacial retreat (19 000–22 000 years bp). Our results suggest that ice sheets linked to major glacial events not only impact genetic structuring in temperate seabirds, but that sea level changes in the tropics associated with these same events have also significantly impacted contemporary genetic structuring in tropical seabird species.     

Molecular markers provide insights into contemporary and historic gene flow for a non‐migratory species

Hairy woodpeckers Picoides villosus are a common, year round resident with distinct plumage and morphological variation across North America. We genotyped 335 individuals at six variable microsatellite loci and analyzed 322 mtDNA control region sequences in order to examine the role of contemporary and historical barriers to gene flow. In addition we combined genetic analyses with ecological niche modelling to test if hairy woodpeckers were isolated in northern refugia (Alaska, Newfoundland and the Queen Charlotte Islands) during the last glacial maximum. Genetic analyses revealed that gene flow among North American hairy woodpecker populations is restricted, but not to the extent predicted for a sedentary species. Populations clustered into two main genetic groups, east and west of the Great Plains in the south and the Rocky Mountains in the north. Contact zones between the two main genetic groups exist in central British Columbia and Washington, but are narrow. Within each group we found additional population structure with genetic breaks between subgroups in the geographic west corresponding to breaks in forested habitat and physical barriers like open expanses of water. Population genetic patterns for hairy woodpeckers have resulted from isolation in multiple southern refugia with the current distribution of genetic groups resulting from post‐glacial expansion and subsequent reduction in gene flow. While populations in Alaska, Newfoundland and the Queen Charlotte Islands are genetically distinct from other populations, we found no evidence of these areas acting as refugia throughout the Pleistocene. Atlantic Canada populations contained unique haplotypes raising the possibility of a separate colonization from the rest of eastern Canada. The endemic subspecies on the island of Newfoundland is not genetically distinct from their closest mainland population unlike the Queen Charlotte Island subspecies.     

Contemporary population structure and post‐glacial genetic demography in a migratory marine species,the blacknose shark,Carcharhinus acronotus

Patterns of population structure and historical genetic demography of blacknose sharks in the western North Atlantic Ocean were assessed using variation in nuclear‐encoded microsatellites and sequences of mitochondrial (mt)DNA. Significant heterogeneity and/or inferred barriers to gene flow, based on microsatellites and/or mtDNA, revealed the occurrence of five genetic populations localized to five geographic regions: the southeastern U.S Atlantic coast, the eastern Gulf of Mexico, the western Gulf of Mexico, Bay of Campeche in the southern Gulf of Mexico and the Bahamas. Pairwise estimates of genetic divergence between sharks in the Bahamas and those in all other localities were more than an order of magnitude higher than between pairwise comparisons involving the other localities. Demographic modelling indicated that sharks in all five regions diverged after the last glacial maximum and, except for the Bahamas, experienced post‐glacial, population expansion. The patterns of genetic variation also suggest that the southern Gulf of Mexico may have served as a glacial refuge and source for the expansion. Results of the study demonstrate that barriers to gene flow and historical genetic demography contributed to contemporary patterns of population structure in a coastal migratory species living in an otherwise continuous marine habitat. The results also indicate that for many marine species, failure to properly characterize barriers in terms of levels of contemporary gene flow could in part be due to inferences based solely on equilibrium assumptions. This could lead to erroneous conclusions regarding levels of connectivity in species of conservation concern.     

Comparative population structure of Cynopterus fruit bats in peninsular Malaysia and southern Thailand

The extent to which response to environmental change is mediated by species-specific ecology is an important aspect of the population histories of tropical taxa. During the Pleistocene glacial cycles and associated sea level fluctuations, the Sunda region in Southeast Asia experienced concurrent changes in landmass area and the ratio of forest to open habitat, providing an ideal setting to test the expectation that habitat associations played an important role in determining species' response to the opportunity for geographic expansion. We used mitochondrial control region sequences and six microsatellite loci to compare the phylogeographic structure and demographic histories of four broadly sympatric species of Old World fruit bats in the genus, Cynopterus. Two forest-associated species and two open-habitat generalists were sampled along a latitudinal transect in Singapore, peninsular Malaysia, and southern Thailand. Contrary to expectations based on habitat associations, the geographic scale of population structure was not concordant across ecologically similar species. We found evidence for long and relatively stable demographic history in one forest and one open-habitat species, and inferred non-coincident demographic expansions in the second forest and open-habitat species. Thus, while these results indicate that Pleistocene climate change did not have a single effect on population structure across species, a correlation between habitat association and response to environmental change was supported in only two of four species. We conclude that interactions between multiple factors, including historical and contemporary environmental change, species-specific ecology and interspecific interactions, have shaped the recent evolutionary histories of Cynopterus fruit bats in Southeast Asia.     

Genetic evidence for the origins of range disjunctions in the Australian dry sclerophyll plant Hardenbergia violacea

Aim The distribution of genetic variation in the Australian dry sclerophyll plant Hardenbergia violacea (Fabaceae) is examined in the context of Pleistocene climate change in order to identify likely refugia. Particular consideration is given to the origin of range disjunctions in South Australia and Tasmania, and to determining whether the Tasmanian population is indigenous or recently introduced from mainland Australia. Location Southeastern Australian mainland and Tasmania. Methods A combination of chloroplast polymerase chain reaction–restriction fragment length polymorphism and genomic amplified fragment length polymorphism (AFLP) marker systems was used to examine the genetic structure of 292 individuals from 13 populations across the range of H. violacea in southeastern Australia. Results Hardenbergia violacea populations in Tasmania and southern Victoria were characterized by low, almost monotypic chloroplast diversity. New South Wales showed higher haplotype diversity and haplotype sharing among widely distributed populations. Principal coordinates analysis (PCoA) of the AFLP data found a strong latitudinal cline in AFLP variation from northern New South Wales south to Tasmania. The Tasmanian population formed an isolated and somewhat disjunct genetic cluster at one end of this cline. However, the South Australian population was an exception to the clinal variation shown by all other populations, forming a highly disjunct cluster in the PCoA. Within‐population genetic diversity was low in both disjunct populations. Main conclusions The genetic evidence indicates that the Tasmanian population is likely to be indigenous and probably the product of vicariance, which was followed by range contraction at the Last Glacial Maximum or an earlier glacial event. The deep phylogenetic disjunction in South Australia is evidence of a much earlier separation on mainland Australia. The chloroplast structure indicates that, during the Pleistocene, H. violacea underwent broad‐scale recolonization in southern Victoria and Tasmania, possibly from a large continental refugium in eastern New South Wales. We conclude that H. violacea, and presumably the sclerophyll communities in which it occurs, have undergone multiple range contractions to large continental refugia during different Pleistocene glaciations in southeastern Australia.     

Chloroplast evidence for geographic stasis of the Australian bird‐dispersed shrub Tasmannia lanceolata (Winteraceae)

Few chloroplast‐based genetic studies have been undertaken for plants of mesic temperate forests in the southern hemisphere and fossil‐based models have provided evidence of vegetation history only at the broadest scales in this region. This study investigates the chloroplast DNA phylogeography of Tasmannia lanceolata (Winteraceae), a fleshy‐fruited, bird‐dispersed shrub that is widespread in the mountains of southeastern Australia and Tasmania. Thirty haplotypes were identified after sequencing 3206 bp of chloroplast DNA in each of 244 individuals collected across the species’ range. These haplotypes showed unexpectedly strong phylogeographic structuring, including a phylogeographic break within a continuous part of the species’ range, with the distribution of four major clades mostly not overlapping, and geographic structuring of haplotypes within these clades. This strong geographic patterning of chloroplast DNA provided evidence for the survival of T. lanceolata in multiple putative wet forest refugia as well as evidence for additional wet forest species refugia in southeastern Australia. In western Tasmania lower haplotype diversity below the LGM tree line compared to above the LGM tree line suggests that glacial refugia at high altitudes may have been important for T. lanceolata. The level of geographic structuring in T. lanceolata is similar to gravity dispersed southern hemisphere plants such as Nothofagus and Eucalyptus. Behavioural traits of the birds transporting seed may have had a strong bearing on the limited transport of T. lanceolata seed, although factors limiting establishment, possibly including selection, may also have been important.     

MITOCHONDRIAL DNA VARIATION IN THE FIELD VOLE (MICROTUS AGRESTIS): REGIONAL POPULATION STRUCTURE AND COLONIZATION HISTORY

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.     

Biogeography of a southern hemisphere freshwater fish: how important is marine dispersal?

Galaxias maculatus is one of the world's most widely distributed freshwater fish. This species has a marine-tolerant juvenile phase, and a geographical range extending through much of the southern hemisphere. We conducted phylogeographic analyses of 163 control region haplotypes of G. maculatus, including samples from New Zealand (five locations), Tasmania (one location) and Chile (one location). A lack of genetic structure among New Zealand samples suggests that marine dispersal facilitates considerable gene flow on an intra-continental scale. The discovery of a Tasmanian-like haplotype in one of 144 New Zealand samples indicates that inter-continental marine dispersal occurs but is insufficient to prevent mitochondrial DNA differentiation among continents. The sister relationship of Tasmanian and New Zealand clades implies that marine dispersal is an important biogeographical mechanism for this species. However, a vicariant role in the divergence of eastern and western Pacific G. maculatus cannot be rejected.     

Chloroplast DNA phylogeography of a distylous shrub (Palicourea padifolia, Rubiaceae) reveals past fragmentation and demographic expansion in Mexican cloud forests

Several phylogeographic studies in northern Mesoamerica have examined the influence of Pleistocene glaciations on the genetic structure of temperate tree species with their southern limit by the contact zone between species otherwise characteristic of North or South America, but few have featured plant species that presumably colonized northern Mesoamerica from South America. A phylogeographical study of Palicourea padifolia, a fleshy-fruited, bird dispersed distylous shrub, was conducted to investigate genetic variation at two chloroplast regions (trnS-trnG and rpl32-trnL) across cloud forest areas to determine if such patterns are consistent with the presence of Pleistocene refugia and/or with the historical fragmentation of the Mexican cloud forests. We conducted population and spatial genetic analyses as well as phylogenetic and isolation with migration analyses on 122 individuals from 22 populations comprising the distribution of P. padifolia in Mexico to gain insight of the evolutionary history of these populations. Twenty-six haplotypes were identified after sequencing 1389 bp of chloroplast DNA. These haplotypes showed phylogeographic structure (N(ST) = 0.508, G(ST) = 0.337, N(ST) > G(ST), P < 0.05), including a phylogeographic break at the Isthmus of Tehuantepec, with private haplotypes at either side of the isthmus, and a divergence time of the split in the absence of gene flow dating back c. 309,000-103,000 years ago. The patterns of geographic structure found in this study are consistent with past fragmentation and demographic range expansion, supporting the role of the Isthmus of Tehuantepec as a biogeographical barrier in the dispersal of P. padifolia. Our data suggest that P. padifolia populations were isolated throughout glacial cycles by the Isthmus of Tehuantepec, accumulating genetic differences due to the lack of migration across the isthmus in either direction, but the results of our study are not consistent with the existence of the previously proposed Pleistocene refugia for rain forest plant species in the region.     

Contrasting phylogeographical patterns for springtails reflect different evolutionary histories between the Antarctic Peninsula and continental Antarctica

Aim  We examined the genetic structure among populations and regions for the springtails Cryptopygus antarcticus antarcticus and Gomphiocephalus hodgsoni (Collembola) to identify potential historical refugia and subsequent colonization routes, and to examine population growth/expansion and relative ages of population divergence.
Location  Antarctic Peninsula for C. a. antarcticus ; Antarctic continent (southern Victoria Land) for G. hodgsoni .
Methods  Samples were collected from 24 and 28 locations across the Antarctic Peninsula and southern Victoria Land regions for C. a. antarcticus and G. hodgsoni , respectively. We used population genetic, demographic and nested clade analyses based on mitochondrial DNA (cytochrome c oxidase subunit I and subunit II).
Results  Both species were found to have population structures compatible with the presence of historical glacial refugia on Pleistocene (2 Ma–present) time-scales, followed by post-glacial expansion generating contemporary geographically isolated populations. However, G. hodgsoni populations were characterized by a fragmented pattern with several 'phylogroups' (likely ancestral haplotypes present in high frequency) retaining strong ancestral linkages among present-day populations. Conversely, C. a. antarcticus had an excess of rare haplotypes with a much reduced volume of ancestral lineages, possibly indicating historical founder/bottleneck events and widespread expansion.
Main conclusions  We infer that these differences reflect distinct evolutionary histories in each locality despite the resident species having similar life-history characteristics. We suggest that this has predominantly been influenced by variation in the success of colonization events as a result of intrinsic historical glaciological differences between the Antarctic Peninsula and continental Antarctic environments.     

Strong population genetic structure and contrasting demographic histories for the small-spotted catshark (Scyliorhinus canicula) in the Mediterranean Sea

Coastal and demersal chondrichthyans, such as the small-spotted catshark, are expected to exhibit genetic differentiation in areas of complex geomorphology like the Mediterranean Basin because of their limited dispersal ability. To test this hypothesis, we used a fragment of the mitochondrial cytochrome c oxidase subunit I gene and 12 nuclear microsatellite loci in order to investigate the genetic structure and historical demography of this species, and to identify potential barriers to gene flow. Samples were collected from the Balearic Islands, the Algerian Basin, the Ionian Sea, the Corinthian Gulf and various locations across the Aegean Sea. Additional sequences from the Atlantic and the Levantine Basin retrieved from GenBank were included in the mitochondrial DNA analysis. Both mitochondrial and nuclear microsatellite DNA data revealed a strong genetic subdivision, mainly between the western and eastern Mediterranean, whereas the Levantine Basin shared haplotypes with both areas. The geographic isolation of the Mediterranean basins seems to enforce the population genetic differentiation of the species, with the deep sea acting as a strong barrier to its dispersal. Contrasting historical demographic patterns were also observed in different parts of the species'' distribution, most notably a population growth trend in the western Mediterranean/Atlantic area and a slight decreasing one in the Aegean Sea. The different effects of the Pleistocene glacial periods on the habitat availability may explain the contrasting demographic patterns observed. The current findings suggest that the small-spotted catshark exhibits several genetic stocks in the Mediterranean, although further study is needed.     

American marten (Martes americana) in the Pacific Northwest: population differentiation across a landscape fragmented in time and space

American marten (Martes americana) have a close association with mature temperate forests, a habitat that expanded throughout the Pacific Northwest as glaciers receded at the end of the Pleistocene. Similar to several other forest-associated mammals in North America (e.g. black bear), genetic analysis of the marten shows a deep phylogeographical subdivision that reflects populations with distinctive evolutionary histories. Using a suite of 14 microsatellite markers, we explored the genetic structure of marten populations in two reciprocally monophyletic clades in the Pacific Northwest identified previously as M. caurina and M. americana by mitochondrial haplotypes and morphology. Microsatellite phylogeographical patterns were congruent with mitochondrial analyses. These independent data sets shed light upon hybridization patterns, population structure and evolutionary histories. Hybridization between M. caurina and M. americana individuals was documented in two regions of sympatry (Kuiu Island in southeastern Alaska and southern Montana). Northern insular populations of M. caurina exhibited higher differentiation and lower variability relative to northern populations of M. americana. Greater divergence among M. caurina populations may reflect longer isolation and persistence in coastal forest habitat that was fragmented by rising sea level in the early Holocene. Lower differentiation among northern M. americana populations and close relationship to other continental M. americana populations may reflect more recent expansion into the Pacific Northwest and/or continued gene flow among populations. Differentiation among M. caurina populations was attributed to habitat fragmentation (i.e. rising sea level), as opposed to isolation-by-distance; oceanic straits pose significant barriers to gene flow among M. caurina populations and between populations of M. caurina and M. americana.