Phylogeography of noble crayfish (Astacus astacus) reveals multiple refugia

相似文献   

Population genetic structure after 125 years of stocking in sea trout (<Emphasis Type="Italic">Salmo trutta</Emphasis> L.)

Stocking can be an effective management and conservation tool, but it also carries the danger of eroding natural population structure, introducing non-native strains and reducing genetic diversity. Sea trout, the anadromous form of the brown trout (Salmo trutta), is a highly targeted species that is often managed by stocking. Here, we assess the present-day population genetic structure of sea trout in a backdrop of 125 years of stocking in Northern Germany. The study area is characterized by short distances between the Baltic and North Sea river watersheds, historic use of fish from both watersheds for stocking, and the creation of a potential migration corridor between the Baltic and North Sea with the opening of the Kiel Canal 120 years ago. A survey of 24 river systems with 180 SNPs indicates that moderate but highly significant population genetic structure has persisted both within and between the Baltic and North Sea. This genetic structure is characterized by (i) heterogeneous patterns of admixture between the Baltic and North Sea that do not correlate with distance from the Kiel Canal and are therefore likely due to historic stocking practises, (ii) genetic isolation by distance in the Baltic Sea at a spatial scale of <?200 km that is consistent with the homing behaviour of sea trout, and (iii) at least one genetically distinct Baltic Sea river system. In light of these results, we recommend keeping fish of North Sea and Baltic Sea origin separate for stocking, and restricting Baltic Sea translocations to neighbouring river systems.     

Dispersal of the Ponto-Caspian amphipod Echinogammarus ischnus: invasion waves from the Pleistocene to the present

The geographical range of the amphipod crustacean Echinogammarus ischnus has expanded over the past century from the Ponto-Caspian region to Western Europe, the Baltic Sea, and the Great Lakes of North America. The present study explores the phylogeographic patterns of this amphipod across its current distribution, based on an examination of nucleotide diversity in the mitochondrial cytochrome c oxidase subunit I (COI) gene. Marked genetic divergence exists among populations of E. ischnus from the Black and Caspian Seas, as well as those from the drainage system of the Black Sea. This divergence suggests the prolonged geographic isolation of these native populations, reflecting the limited dispersal capability of E. ischnus. By contrast, invading populations are characterized by a lack of genetic variation; a single mitochondrial genotype of Black Sea origin has colonized sites from the Rhine River to North America. The dispersal pattern in E. ischnus is very similar to that in the Ponto-Caspian cladoceran Cercopagis pengoi. Despite their contrasting life history strategies, these invading species followed the same route of invasion from the northern Black Sea to the Baltic Sea region, and subsequently to North America.     

Microsatellite variation in cod Gadus morhua throughout its geographic range

Previous genetic studies using neutral markers such as allozymes, mtDNA and minisatellite loci have demonstrated varying amounts of population structure in cod Gadus morhua throughout the Atlantic. Microsatellite loci, which are potentially the most informative of presently available neutral genetic markers, have been applied extensively within western and eastern Atlantic areas but not on a range-wide basis. In the present study, six microsatellite DNA loci were used to screen cod samples from nine locations throughout the geographic range from the Scotian Shelf in the West Atlantic to the Barents and Baltic Seas in the east. Overall F _ST value was 0·03 ( P = < 0·001) across all samples. Statistically significant population differences over all loci combined were evident between more geographically distant samples, using either heterogeneity tests or F _ST analysis, with at least one locus showing significant differences between all samples (prior to Bonferroni correction). A significant correlation was observed between genetic and geographical distance, suggesting a higher level of historical and contemporary gene flow between adjacent populations than more distant populations. Samples from either end of the geographic range (Scotian Shelf and Baltic Sea) were particularly distinct when analysed using the STRUCTURE programme and also showed a high level of self-assignment when individuals of either the Scotian Shelf or Baltic Sea were tested against the entire data set. The present microsatellite study demonstrates a high level of geographic population structure between the western Atlantic, middle and eastern Atlantic and Baltic Sea, and thus, the findings should be useful in devising overall management and conservation strategies for the species.     

Genetic population structure of turbot (Scophthalmus maximus L.) supports the presence of multiple hybrid zones for marine fishes in the transition zone between the Baltic Sea and the North Sea

Genetic population structure of turbot (Scophthalmus maximus L.) in the Northeast Atlantic was investigated using eight highly variable microsatellite loci. In total 706 individuals from eight locations with temporal replicates were assayed, covering an area from the French Bay of Biscay to the Aaland archipelago in the Baltic Sea. In contrast to previous genetic studies of turbot, we found significant genetic differentiation among samples with a maximum pairwise FST of 0.032. Limited or no genetic differentiation was found among samples within the Atlantic/North Sea area and within the Baltic Sea, suggesting high gene flow among populations in these areas. In contrast, there was a sharp cline in genetic differentiation going from the low saline Baltic Sea to the high saline North Sea. The data were explained best by two divergent populations connected by a hybrid zone; however, a mechanical mixing model could not be ruled out. A significant part of the genetic variance could be ascribed to variation among years within locality. Nevertheless, the population structure was relatively stable over time, suggesting that the observed pattern of genetic differentiation is biologically significant. This study suggests that hybrid zones are a common phenomenon for marine fishes in the transition area between the North Sea and the Baltic Sea and highlights the importance of using interspecific comparisons for inferring population structure in high gene flow species such as most marine fishes.     

Mitochondrial Control Region and microsatellite analyses on harbour porpoise (Phocoena phocoena) unravel population differentiation in the Baltic Sea and adjacent waters

The population status of the harbour porpoise (Phocoena phocoena) in the Baltic area has been a continuous matter of debate. Here we present the by far most comprehensive genetic population structure assessment to date for this region, both with regard to geographic coverage and sample size: 497 porpoise samples from North Sea, Skagerrak, Kattegat, Belt Sea, and Inner Baltic Sea were sequenced at the mitochondrial Control Region and 305 of these specimens were typed at 15 polymorphic microsatellite loci. Samples were stratified according to sample type (stranding vs. by-caught), sex, and season (breeding vs. non-breeding season). Our data provide ample evidence for a population split between the Skagerrak and the Belt Sea, with a transition zone in the Kattegat area. Among other measures, this was particularly visible in significant frequency shifts of the most abundant mitochondrial haplotypes. A particular haplotype almost absent in the North Sea was the most abundant in Belt Sea and Inner Baltic Sea. Microsatellites yielded a similar pattern (i.e., turnover in occurrence of clusters identified by STRUCTURE). Moreover, a highly significant association between microsatellite assignment and unlinked mitochondrial haplotypes further indicates a split between North Sea and Baltic porpoises. For the Inner Baltic Sea, we consistently recovered a small, but significant separation from the Belt Sea population. Despite recent arguments that separation should exceed a predefined threshold before populations shall be managed separately, we argue in favour of precautionary acknowledging the Inner Baltic porpoises as a separate management unit, which should receive particular attention, as it is threatened by various factors, in particular local fishery measures.     

Phylogeographic evidence for the postglacial colonization of the North and Baltic Sea coasts from inland glacial refugia by Triglochin maritima L.

We investigated the geographical distribution of genetic variation in 67 individuals of Triglochin maritima from 38 localities across Europe using AFLP markers. Analysis of genetic variation resulted in the recognition of two major genetic groups. Apart from few geographical outliers, these are distributed (1) along the Atlantic coasts of Portugal, Spain and France and (2) in the North Sea area, the Baltic Sea area, at central European inland localities, the northern Adriatic Sea coast and the Mediterranean coast of southwest France. Considering possible range shifts of T. maritima in reaction to Quaternary climatic changes as deduced from the present-day northern temperature limit of the species, Quaternary changes of coastline in the North Sea area and the very recent origin of the Baltic Sea, we conclude that the coastal populations of T. maritima in the North Sea and Baltic Sea areas originated from inland populations.     

Realization of the project for Acipenser oxyrhynchus oxyrhynchus restoration in the basin of the Neman River

The results of the works on the international project for the Baltic sturgeon restoration in the basin of the Neman River are considered. The mutual goal of the project is the restoration of the Baltic sturgeon population in its whole former area in the Baltic Sea. Successful works on the restoration of the Baltic sturgeon population are conducted in the Oder and the Vistula basins. The stockings of the Neman River with the sturgeon fry were started from 2012 year. It is contemplated that the sturgeon stockings of the main rivers of the Baltic Sea will enable to restore local sturgeon populations in these river basins. Till the beginning of the XXI century it was supposed that the Atlantic sturgeon Acipenser sturio had inhabited the Baltic Sea, but numerous genetic analysis of the samples of the sturgeon bones from the archeological finds in the museums showed that the Baltic Sea had been inhabited with Acipenser oxyrhynchus and its population still inhabits several rivers in Canada. This discovery permitted to start the creation of the Baltic sturgeon broodstock. Sturgeon fry from the eggs imported from Canada were used for stocking at the first stage of the project. Later it is contemplated to use the fry from the broodstocks in Germany and Poland. Sturgeon fry hatched from Canadian eggs in Poland and reared in Lithuania was used for the Neman River stocking. The fry were tagged and released in the Neris and the Sventoji Rivers in the Neman River basin. The sturgeon migrated into the Curonian lagoon where the monitoring of the catches was fulfilled. The results of sturgeon catches monitoring are discussed.     

Adaptive and Neutral Genetic Variation and Colonization History of Atlantic Salmon, Salmo salar

Synopsis I combined neutral microsatellite markers with the major histocompatibility complex (MHC) class IIB to study genetic differentiation and colonization history in Atlantic salmon, Salmo salar, in the Baltic Sea and in the north-eastern Atlantic. Baltic salmon populations have lower levels of microsatellite genetic variation, in terms of heterozygosity and allelic richness than Atlantic populations, confirming earlier findings with other genetic markers, suggesting that the Baltic Sea populations have been exposed to genetic bottlenecks, most likely at a founding event. On the other hand, the level of MHC variation was similar in the Baltic and in the north-eastern Atlantic, indicating that positive balancing selection has increased the level of MHC-variation. Both microsatellite and MHC class IIB genetic variation give strong support to the hypothesis that the Baltic salmon are of a biphyletic origin, the southern population in this study is strongly differentiated from both the northern Baltic salmon populations and from the north-eastern Atlantic populations. Salmon may have colonized the northern Baltic Sea either from the south, via the so called “N?rke strait” or from the north, via a proposed historical connection between the White Sea and the northern Baltic. At microsatellites, no significant isolation-by distance was found at either colonization route. At the MHC, populations were significantly isolated by distance when assuming that colonization occurred via the “N?rke strait”.     

Phenotypical characterization of indigenous freshwater crayfish populations

The morphology of an animal is known to reflect both genetic variation and adaptation to the environment. Thus, phenotypic criteria have been used to characterize indigenous crayfish populations. Twenty-one morphometric parameters were measured on crayfish from 25 waterbodies in the Austrian and Italian parts of Tyrol. They were analysed with hierarchical cluster analysis to obtain the population structure based on morphological similarity between and within the freshwater crayfish species Astacus astacus (noble crayfish), Austropotamobius torrentium (stone crayfish) and Austropotamobius pallipes (white-clawed crayfish). Furthermore, a stepwise discriminant analysis was applied to the morphometric data to test their differentiating power between populations. Both analyses resulted in a clear differentiation of species and populations, and reflected geographic separations. Thus, the developed morphometric methods were shown to be applicable to characterize the phenotype in freshwater crayfish and seem appropriate to be used for stock identification and the effective characterization of management units in decapod crustaceans.     

Local adaptation and oceanographic connectivity patterns explain genetic differentiation of a marine diatom across the North Sea–Baltic Sea salinity gradient

Drivers of population genetic structure are still poorly understood in marine micro‐organisms. We exploited the North Sea–Baltic Sea transition for investigating the seascape genetics of a marine diatom, Skeletonema marinoi. Eight polymorphic microsatellite loci were analysed in 354 individuals from ten locations to analyse population structure of the species along a 1500‐km‐long salinity gradient ranging from 3 to 30 psu. To test for salinity adaptation, salinity reaction norms were determined for sets of strains originating from three different salinity regimes of the gradient. Modelled oceanographic connectivity was compared to directional relative migration by correlation analyses to examine oceanographic drivers. Population genetic analyses showed distinct genetic divergence of a low‐salinity Baltic Sea population and a high‐salinity North Sea population, coinciding with the most evident physical dispersal barrier in the area, the Danish Straits. Baltic Sea populations displayed reduced genetic diversity compared to North Sea populations. Growth optima of low salinity isolates were significantly lower than those of strains from higher native salinities, indicating local salinity adaptation. Although the North Sea–Baltic Sea transition was identified as a barrier to gene flow, migration between Baltic Sea and North Sea populations occurred. However, the presence of differentiated neutral markers on each side of the transition zone suggests that migrants are maladapted. It is concluded that local salinity adaptation, supported by oceanographic connectivity patterns creating an asymmetric migration pattern between the Baltic Sea and the North Sea, determines genetic differentiation patterns in the transition zone.     

Evidence of a hybrid-zone in Atlantic cod (Gadus morhua) in the Baltic and the Danish Belt Sea revealed by individual admixture analysis

The study of hybrid zones is central to our understanding of the genetic basis of reproductive isolation and speciation, yet very little is known about the extent and significance of hybrid zones in marine fishes. We examined the population structure of cod in the transition area between the North Sea and the Baltic Sea employing nine microsatellite loci. Genetic differentiation between the North Sea sample and the rest increased along a transect to the Baltic proper, with a large increase in level of differentiation occurring in the Western Baltic area. Our objective was to determine whether this pattern was caused purely by varying degrees of mechanical mixing of North Sea and Baltic Sea cod or by interbreeding and formation of a hybrid swarm. Simulation studies revealed that traditional Hardy-Weinberg analysis did not have sufficient power for detection of a Wahlund effect. However, using a model-based clustering method for individual admixture analysis, we were able to demonstrate the existence of intermediate genotypes in all samples from the transition area. Accordingly, our data were explained best by a model of a hybrid swarm flanked by pure nonadmixed populations in the North Sea and the Baltic Sea proper. Significant correlation of gene identities across loci (gametic phase disequilibrium) was found only in a sample from the Western Baltic, suggesting this area as the centre of the apparent hybrid zone. A hybrid zone for cod in the ecotone between the high-saline North Sea and the low-saline Baltic Sea is discussed in relation to its possible origin and maintenance, and in relation to a classical study of haemoglobin variation in cod from the Baltic Sea/Danish Belt Sea, suggesting mixing of two divergent populations without interbreeding.     

Mitochondrial phylogeography of the European sprat (Sprattus sprattus L., Clupeidae) reveals isolated climatically vulnerable populations in the Mediterranean Sea and range expansion in the northeast Atlantic

We examined the genetic structure of the European sprat ( Sprattus sprattus ) by means of a 530-bp sequence of the mitochondrial control region from 210 fish originating from seven sampling localities of its distributional range. Phylogeographical analysis of 128 haplotypes showed a phylogenetic separation into two major clades with the Strait of Sicily acting as a barrier to gene flow between them. While no population differentiation was observed based on analysis of molecular variance and net nucleotide differences between samples of the Baltic Sea, the North Sea and the Bay of Biscay nor between the Black Sea and the Bosporus, a strong population differentiation between these samples and two samples from the Mediterranean Sea was found. Further, the biggest genetic distance was observed within the Mediterranean Sea between the populations of the Gulf of Lyon and the Adriatic Sea, indicating genetic isolation of these regions. Low genetic diversities and star-like haplotype networks of both Mediterranean Sea populations point towards recent demographic expansion scenarios after low population size, which is further supported by negative F _S values and unimodal mismatch distributions with a low mean. Along the northeast Atlantic coast, a northwards range expansion of a large and stable population can be assumed. The history of a diverse but differentiated Black Sea population remains unknown due to uncertainties in the palaeo-oceanography of this sea. Our genetic data did not confirm the presently used classification into subspecies but are only preliminary in the absence of nuclear genetic analyses.     

Microsatellite and mtDNA analysis of the population structure of grey seals (Halichoerus grypus) from three breeding areas in the Baltic Sea

The growing number of grey seals in the Baltic Sea has led to a dramatic increase in interactions between seals and fisheries. The conflict has become such a problem that hunting was introduced in Finland in 1998 and the Swedish Environment Protection Agency recommended a cull of grey seals starting in 2001. Culling has been implemented despite the lack of data on population structure. Low levels of migration between regions would mean that intensive culling in specific geographic areas would have disproportionate effects on local population structure and genetic diversity. We used eight microsatellite loci and a 489 bp section of the mtDNA control region to examine the genetic variability and differentiation between three breeding sites in the Baltic Sea and two in the UK. We found high levels of genetic variability in all sampled Baltic groups for both the microsatellites and the control region. There were highly significant differences in microsatellite allele frequencies between all three Baltic breeding sites and between the Baltic sites and the UK sites. However, there were no significant differences in mtDNA control region haplotypes between the Baltic sites. This genetic substructure of the Baltic grey seal populations should be taken into consideration when managing the seal population to prevent the hunting regime from having an adverse effect on genetic diversity by setting hunting quotas separately for the different subpopulations. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The LWb blood group as a marker of prehistoric Baltic migrations and admixture.

Archaeological findings and historical records indicate frequent migrations and exchange of genetic material between populations in the Baltic Sea area. However, there have so far been very few attempts to trace migrations in this area using genetic markers. We have studied the Baltic populations with respect to exceptional variations in the frequencies of the Landsteiner-Wiener (LW) blood group. The frequency of the uncommon LWb gene was high in the Balts, around 6% among Latvians and Lithuanians, very low among the other western Europeans (0-0.1%) and apparently absent in Asiatic and African populations. From the Baltic region of peak frequency there was a regular decline of LWb incidence (a descending cline) in the neighboring populations: 4.0% in the Estonians, 2.9% in the Finns, 2. 2% in the Vologda Russians, and 2.0% in the Poles. Thus the distribution of LWb suggests considerable and extensive Baltic admixture, especially in the north and northeast direction. In Southern Sweden with an LWb frequency of 0.3%, the Baltic influence appeared slight, while in the population of the Swedish island Gotland in the middle of the Baltic Sea there was a significantly increased LWb frequency of 1.0% compared with that of Western European countries. The distinction of codominantly inherited LW antigenic forms, LWa and LWb (previously Nea), is known to be due to a single base substitution. Based on our population data, it is plausible that the expansion of this point mutation occurred only once during human history. Furthermore, our data indicate that the expansion of the LWb mutation occurred in Balts and that LWb can be considered a 'Baltic tribal marker', its presence in other populations being an indicator of the degree of Baltic genetic influence.     

Genetic assessment of spatiotemporal evolutionary relationships and stocking effects in grayling (Thymallus thymallus, Salmonidae)

Domestically reared introduced (or escaped) individuals can have detrimental genetic effects on the indigenous populations into which they are released. Consequently, numerous studies have attempted to estimate whether non-native specimens have contributed to the gene pool of wild populations. So far, the key limiting factor of such studies has been their lack of appropriate baseline genetic material. Here, microsatellite DNA analyses of historical scale samples and contemporary wild and introduced populations were used to assess spatiotemporal population structure and stocking effects among endangered Lake Saimaa (eastern Finland) grayling ( Thymallus thymallus , Salmonidae). Significant decreases in genetic differentiation were detected between wild and introduced populations since the commencement of stocking in 1986. Accordingly, up to 15% of the contemporary wild grayling were confidently identified to be of pure hatchery origin, and recent hybridization between the hatchery and indigenous individuals appeared likely. Despite these clear genetic imprints of stocking, the contemporary populations exhibited evolutionary relationships congruent with the sampling locations, and up to 73% of contemporary individuals were identified to be of pure indigenous origin. The use of historical baseline material should prove efficient for monitoring gene flow between domesticated and wild populations in other species also, e.g. salmonids, game animals and plants.     

Genetic characterization of Western European noble crayfish populations (<Emphasis Type="Italic">Astacus astacus</Emphasis>) for advanced conservation management strategies

One central goal of conservation biology is to conserve the genetic diversity of species in order to protect their adaptive potential. The main objective of this study was to identify management units (MUs) for the threatened noble crayfish (Astacus astacus) in Western Europe by utilizing sequence and microsatellite analysis to determine populations in need of focused conservation programs. With the analysis of noble crayfish from 31 sampling sites from Belgium, France, The Netherlands and Germany, and further comparison of this data with a European-wide dataset, we propose four distinct MUs: the French Meuse (MU 1), the French Rhine (MU 2), the Belgian Scheldt and Meuse (MU 3) as well as populations from the French Seine (MU 4). This knowledge enables advanced A. astacus conservation management practises in these catchments by distinguishing between outbreeding and inbreeding populations and by preserving the maximum genetic diversity. When required, a high genetic diversity can be conserved by strengthen existing populations via stocking with populations that either bear the most common haplotype or population-specific private haplotypes in order to maintain recent and regional adaptions. Above all, stocking with populations that exhibit haplotypes from outside Western Europe should be avoided in these catchments. This study supports the preservation of the genetic diversity of noble crayfish in Western Europe and provides thus a proposition for advanced conservation management.     

Identification of the origin of an Atlantic salmon (Salmo salar L.) population in a recently recolonized river in the Baltic Sea

The founder event in a recently recolonized salmon population in the Baltic Sea (Gulf of Finland) was investigated. To identify the origin of the founders, four wild populations and two hatchery stocks were analysed using six microsatellite loci. The results of assignment tests and factorial correspondence analysis suggest that the initial recolonizers of the river Selja originated from the geographically nearest (7 km) wild population (river Kunda) but as the result of stocking activities, interbreeding between recolonizers and hatchery individuals has occurred in subsequent years. Although the hatchery releases are outnumbering the wild salmon recruitment in the Baltic Sea at present, our results suggest that the native populations may still have an important role in colonization processes of the former salmon rivers.     

Phylogeography of the common ragworm Hediste diversicolor (Polychaeta: Nereididae) reveals cryptic diversity and multiple colonization events across its distribution

Previous studies on the common ragworm Hediste diversicolor (Polychaeta: Nereididae) revealed a marked genetic fragmentation across its distribution and the occurrence of sibling taxa in the Baltic Sea. These results suggested that the phylogeographic patterns of H. diversicolor could reflect interactions between cryptic differentiation and multiple colonization events. This study aims to describe the large-scale genetic structuring of H. diversicolor and to trace the phylogeographic origins of the genetic types described in the Baltic Sea. Samples of H. diversicolor (2 <  n  < 28) were collected at 16 locations across the NE Atlantic coasts of Europe and Morocco and in the Mediterranean, Black and Caspian Seas and sequenced at two mitochondrial gene fragments (COI and cyt b , 345 and 290 bp, respectively). Bayesian analyses revealed deep phylogeographic splits yielding three main clades corresponding to populations (i) from the NE Atlantic coasts (from Germany to Morocco) and from part of the Western Mediterranean, (ii) from the Mediterranean Sea, and (iii) from the Black and Caspian Seas. These clades are further divided in well-supported subclades including populations from different regions of NE Atlantic and Mediterranean (i.e. Portugal/Morocco, Western Mediterranean, Adriatic Sea). The Baltic Sea comprises three sympatric lineages sharing a common evolutionary history with populations from NE Atlantic, Western Mediterranean and Black/Caspian Seas, respectively. Hence, the current patterns of genetic structuring of H. diversicolor appear as the result of allopatric isolation, multiple colonization events and possible adaptation to local environmental conditions.     

Ancient divisions, recent expansions: phylogeography and population genetics of the round goby Apollonia melanostoma

During the past two decades, the round goby Apollonia melanostoma (= Neogobius melanostomus ) has expanded its range via shipping transport and canals, extending north and west from the Ponto-Caspian region of Eurasia and to the North American Great Lakes. Exotic populations of the round goby have been very successful in the Baltic Sea and the Great Lakes regions, exerting significant ecological changes. Our study evaluates the population genetic and biogeographical structure of the round goby across its native and nonindigenous ranges, in light of geological history and its expansion pathways. We analyzed seven new nuclear microsatellite loci and mitochondrial DNA cytochrome b gene sequences from 432 individuals in 22 locations. Population structure was tested using F _ST-analogs, phylogenetic trees, clustering diagrams, Bayesian assignment tests and nested clade analyses. Results show that native populations in the Black vs. the Caspian Sea basins diverge by 1.4% and c. 350 000 years, corresponding to closure of their prior connections and supporting the taxonomic separation of the Black Sea A. m. melanostoma from the Caspian Sea A. m. affinis . Their within-basin populations diverge by ~0.4% and 100 000 years. Nonindigenous populations in the Baltic Sea and Danube and Dnieper Rivers trace to separate northern Black Sea origins, whereas the upper Volga River system houses mixed populations of A. m. melanostoma and A. m. affinis . Native populations average twice the genetic diversity of most exotic sites; however, sites in the Volga River system have high diversity due to mixing of the two taxa. Our results highlight how vicariance and anthropogenic disturbances have shaped a rapidly expanding species' genetic heritage.