Postglacial Colonization Patterns Research Articles

Next-generation phylogeography resolves post-glacial colonization patterns in a widespread carnivore, the red fox (Vulpes vulpes), in Europe.

Carnivores tend to exhibit a lack of (or less pronounced) genetic structure at continental scales in both a geographic and temporal sense and this can confound the identification of post-glacial colonization patterns in this group. In this study we used genome-wide data (using genotyping by sequencing [GBS]) to reconstruct the phylogeographic history of a widespread carnivore, the red fox (Vulpes vulpes), by investigating broad-scale patterns of genomic variation, differentiation and admixture amongst contemporary populations in Europe. Using 15,003single nucleotide polymorphisms (SNPs) from 524 individuals allowed us to identify the importance of refugial regions for the red fox in terms of endemism (e.g., Iberia). In addition, we tested multiple post-glacial recolonization scenarios of previously glaciated regions during the Last Glacial Maximum using an Approximate Bayesian Computation (ABC) approach that were unresolved from previous studies. This allowed us to identify the role of admixture from multiple source population post-Younger Dryas in the case of Scandinavia and ancient land-bridges in the colonization of the British Isles. A natural colonization of Ireland was deemed more likely than an ancient human-mediated introduction as has previously been proposed and potentially points to a larger mammalian community on the island in the early post-glacial period. Using genome-wide data has allowed us to tease apart broad-scale patterns of structure and diversity in a widespread carnivore in Europe that was not evident from using more limited marker sets and provides a foundation for next-generation phylogeographic studies in other non-model species.

Bioregions are predominantly climatic for fishes of northern lakes

AbstractAimRecurrent species assemblages integrate important biotic interactions and joint responses to environmental and spatial filters that enable local coexistence. Here, we applied a bipartite (site–species) network approach to develop a natural typology of lakes sharing distinct fish faunas and provide a detailed, hierarchical view of their bioregions. We then compared the roles of key biogeographical factors to evaluate alternative hypotheses about how fish communities are assembled from the regional species pool.LocationOntario, Canada and the Upper Midwest, USA.Time period1957–2017.Major taxa studiedFreshwater fishes.MethodsBipartite modularity analysis was performed on 90 taxa from 10,016 inland lakes in the Southwestern Hudson Bay, Mississippi River and St. Lawrence River drainages, uncovering bioregionalization of North American fishes at a large, subcontinental scale. We then used a latent variable approach, pairing non‐metric partial least‐squares structural equation modelling with multiple logistic regression, to show differences in the biogeographical templates of each type of community. Indicators of contemporary and historical connectivity, climate and habitat constructs were estimated using a geographical information system.ResultsFish assemblages reflected broad, overlapping patterns of postglacial colonization, climate and geological setting, but community differentiation was most linked to temperature, precipitation and, for certain groups, lake area and water quality. Bioregions were also marked by non‐native species, showing broad‐scale impacts of introductions to the Great Lakes and surrounding basins.Main conclusionsThe dominant effects of climate across broad spatial gradients indicate differing sensitivities of fish communities to rapidly accelerating climate change and opportunities for targeted conservation strategies. By assessing biological variation at the level of recurrent assemblages, we accounted for the non‐stationarity of macroecological processes structuring different sets of species on the landscape and offer novel inference on the assembly of inland fish communities.

Rethinking long‐term vegetation dynamics: multiple glacial refugia and local expansion of a species complex

Evidence is accumulating that some arcto‐boreal plant taxa persisted through the last glacial maximum (LGM) in Alaska and adjacent Canada. However, the spatial patterns of glacial persistence and associated postglacial colonization remain largely unknown. In this study, we investigated the LGM refugia of an alder (Alnus) species complex (n = 3 taxa) and assess the spatiotemporal dynamics of Alnus in this vast region. Specifically, we conducted high‐throughput DNA sequencing (ddRADseq) on Alnus foliar samples collected from a dense population network to investigate patterns of genetic structure and infer the presence of glacial lineages. Species distribution modeling (SDM) was used to investigate the probability and possible locations of glacial persistence. These analyses were integrated and then compared with fossil pollen data to identify the locations of refugial populations and spatial patterns of postglacial colonization. Our genetic analyses revealed two glacial lineages with separate geographic origins for each Alnus taxon, suggesting that the genus persisted in multiple LGM refugia. Non‐overlapping hindcast distributions based on SDMs further support the presence of multiple, spatially distinct refugia. These ddRADseq and SDM results, in conjunction with reassessment of fossil pollen records, suggest that Alnus expanded from several population nuclei that existed during the LGM and coalesced during the Holocene to form its present range. These results challenge the unidirectional model for postglacial vegetation expansion, implying that climate buffering associated with landscape heterogeneity and adaptation to millennial‐scale environmental variability played important roles in driving late‐Quaternary population dynamics.

Atlantic salmon populations reveal adaptive divergence of immune related genes - a duplicated genome under selection.

BackgroundPopulations of Atlantic salmon display highly significant genetic differences with unresolved molecular basis. These differences may result from separate postglacial colonization patterns, diversifying natural selection and adaptation, or a combination. Adaptation could be influenced or even facilitated by the recent whole genome duplication in the salmonid lineage which resulted in a partly tetraploid species with duplicated genes and regions.ResultsIn order to elucidate the genes and genomic regions underlying the genetic differences, we conducted a genome wide association study using whole genome resequencing data from eight populations from Northern and Southern Norway. From a total of ~4.5 million sequencing-derived SNPs, more than 10 % showed significant differentiation between populations from these two regions and ten selective sweeps on chromosomes 5, 10, 11, 13–15, 21, 24 and 25 were identified. These comprised 59 genes, of which 15 had one or more differentiated missense mutation. Our analysis showed that most sweeps have paralogous regions in the partially tetraploid genome, each lacking the high number of significant SNPs found in the sweeps. The most significant sweep was found on Chr 25 and carried several missense mutations in the antiviral mx genes, suggesting that these populations have experienced differing viral pressures. Interestingly the second most significant sweep, found on Chr 5, contains two genes involved in the NF-KB pathway (nkap and nkrf), which is also a known pathogen target that controls a large number of processes in animals.ConclusionOur results show that natural selection acting on immune related genes has contributed to genetic divergence between salmon populations in Norway. The differences between populations may have been facilitated by the plasticity of the salmon genome. The observed signatures of selection in duplicated genomic regions suggest that the recently duplicated genome has provided raw material for evolutionary adaptation.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2867-z) contains supplementary material, which is available to authorized users.

Founder events and pre-glacial divergences shape the genetic structure of European Collembola species.

BackgroundClimate oscillations in the Cenozoic reduced species richness and genetic diversity of terrestrial and aquatic animals and plants in central and northern Europe. The most abundant arthropods in temperate soils are Collembola that live in almost any soil-related habitat. Extant species show little morphological variation to Eocene fossils, suggesting persistence of species in stable habitats for millions of years. Collembola are able to evade adverse climatic conditions by moving into deeper soil layers and are tolerant to frost and draught. If these adaptations sufficed for surviving glacial periods remains open and needs to be investigated in a phylogeographic context, i.e. investigating spatial structure on molecular level. We investigated the molecular variation of three common species of Collembola at a pan-European scale to identify glacial refuges and post-glacial colonization patterns with three genetic markers.ResultsAll genes revealed remarkable genetic structure between but not within populations, suggesting density dependent processes for establishment of populations (founder-takes-all principle), which is common for European animals and plants. In contrast to the post-glacial recolonization patterns of many aboveground organisms, divergence times of most geographic lineages indicate preservation of genetic structure since the Miocene.ConclusionsCollembola survived severe climatic changes including those during Quatenary glaciation and kept high genetic variance across Europe. Likely the buffering of temperature oscilliations in soil and the ability to evade adverse climatic conditions due to cold-tolerance and horizontal migration enabled Collembola to evade strong selective pressure of abiotic forces.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0719-8) contains supplementary material, which is available to authorized users.

Glacial refugia and post-glacial colonization patterns in European bryophytes

Most species are assumed to have survived south or east of the ice sheet covering northern Europe during the last glacial maximum. Molecular and macrofossil evidence suggests, however, that some species may have survived in ice-free areas in Scandinavia. In plants, inbreeding and vegetative growth are associated with low genetic load and enhanced survival in small, isolated populations. These characteristics are often found in bryophytes, possibly allowing them to survive extreme conditions in isolated refugia and also within ice sheets. Here, we review the Holocene bryophyte history in Europe highlighting main glacial refugia and post-glacial colonization routes. Also, meta-analyses are performed to investigate if distribution ranges and genetic structure are associated with life-history traits. Bryophytes survived the last glaciation in several refugia, but there is no unequivocal evidence of survival within the Scandinavian ice sheet. Northern Europe was colonized from southern, eastern and western Europe, as well as North America. Species with small spores have broader distribution ranges than species with large spores, and high frequency of sporophyte production is associated with limited genetic differentiation between populations.

The rare peat moss Sphagnum wulfianum (Sphagnaceae) did not survive the last glacial period in northern European refugia

Organisms may survive unfavorable conditions either by moving to more favorable areas by means of dispersal or by adapting to stressful environments. Pleistocene glacial periods represent extremely unfavorable conditions for the majority of life forms, especially sessile organisms. Many studies have revealed placements of refugial areas and postglacial colonization patterns of seed plants, but little is still known about areas of long-term survival and historical migration routes of bryophytes. Given overall differences in stress tolerance between seed plants and bryophytes, it is of interest to know whether bryophytes have survived periods of extreme climatic conditions better then seed plants in northern areas. The haploid and rarely spore-producing peat moss Sphagnum wulfianum is mostly found in areas that were covered by ice during the last glacial maximum. Twelve microsatellite markers were amplified from 43 populations (367 shoots) of this species, and data were analyzed using population genetic diversity statistics, Bayesian clustering methods, and coalescence-based inference tools to estimate historical and demographic parameters. Genetic diversity within populations was low, but populations were highly differentiated, with two main genetic clusters being recognized. The two main genetic groups have diverged quite recently in the Holocene, and the pattern of genetic variability and structuring gives no support for survival in Scandinavian refugia during the last glacial period in this species. The dispersal ability of this plant thus seems surprisingly high despite its infrequent spore production.

Microsatellite Genetic Structure and Cytonuclear Discordance in Naturally Fragmented Populations of Deer Mice (Peromyscus maniculatus)

The Great Lakes impose high levels of natural fragmentation on local populations of terrestrial animals in a way rarely found within continental ecosystems. Although separated by major water barriers, woodland deer mouse (Peromyscus maniculatus gracilis) populations on the islands and on the Upper Peninsula (UP) and Lower Peninsula (LP) of Michigan have previously been shown to have a mitochondrial DNA contact zone that is incongruent with the regional landscape. We analyzed 11 microsatellite loci for 16 populations of P. m. gracilis distributed across 2 peninsulas and 6 islands in northern Michigan to address the relative importance of geographical structure and inferred postglacial colonization patterns in determining the nuclear genetic structure of this species. Results showed relatively high levels of genetic structure for this species and a significant correlation between interpopulation differentiation and separation by water but little genetic structure and no isolation-by-distance within each of the 2 peninsulas. Genetic diversity was generally high on both peninsulas but lower and correlated to island size in the Beaver Island Archipelago. These results are consistent with the genetic and demographic isolation of Lower Peninsula populations, which is a matter of concern given the dramatic decline in P. m. gracilis abundance on the Lower Peninsula in recent years.

Genetic relationships of meadow vole (Microtus pennsylvanicus) populations in central Appalachian wetlands

We sequenced and compared variation within a 375-base-pair segment of the mitochondrial DNA control region of 323 meadow voles ( Microtus pennsylvanicus (Ord, 1815)) among 14 populations to determine the influence of past and present landscape connectivity among isolated wetlands in the central Appalachian Mountains. To best explain observed differences among sites, we used genetic and landscape-level (GIS) data to test a null hypothesis (no genetic differences) and three alternate explanations of significant variation owing to founder effects, effective population size, or isolation by distance. Sequencing results revealed 16 distinct haplotypes (1–8 haplotypes/site), with two present in samples from most wetlands, and half of the remaining haplotypes concentrated in specific geographic clusters. Our findings best support the explanation that founder effects have influenced current genetic patterns among sites. These founder effects are likely due to historical land-use activities such as exploitative logging (ca. 1880–1920; creating early successional habitats for voles) and subsequent forest regeneration over the past half century; they were also likely influenced by postglacial colonization patterns. Therefore, current genetic diversity in these populations seems to largely reflect the number and source of voles that successfully colonized these isolated wetlands during the window of opportunity immediately following extensive logging.

Patterns of post-glacial colonization by western redcedar (Thuja plicata, Cupressaceae) as revealed by microsatellite markers

As knowledge of historical migration in response to climatic change allows insight into the dynamic nature of range shifts, patterns of post-glacial colonization were evaluated for the western redcedar ( Thuja plicata Donn ex D. Don). We sampled and genotyped 620 trees from 23 populations across its range, including disjunct coastal and interior mesic sites. Genetic variation at eight microsatellite loci (mean alleles/locus = 10.30, mean expected heterozygosity = 0.755) was much higher than previous studies involving other markers, and inbreeding coefficients were predominantly positive (mean = 0.110). The two southernmost populations showed greatest genetic distances, while remaining populations clustered into three distinct geographic groups, comprising northern–coastal, central, and southern–interior populations, respectively. Genetic diversity decreased with latitude, while genetic and geographic distances were strongly correlated (r = 0.788). Our findings are consistent with independent routes of relatively recent colonization from one major refugium, located south of the glacial maximum, rather than ancient vicariant events. Regional bottlenecks, detected in the south of the range, may have resulted from local extinctions as the range of western redcedar advanced northward. Combined with inbreeding and the evolution of inbreeding tolerance, this may have promoted homozygosity for most classes of genetic markers as observed in other studies of this species.

Microsatellite DNA polymorphism confirms reproductive isolation and reveals differences in population genetic structure of cryptic pipistrelle bat species

Previous studies have indicated that the common European pipistrelle bat (Pipistrellus pipistrellus) comprises two cryptic species, P. pipistrellus and Pipistrellus pygmaeus, which differ in echolocation call frequency and mitochondrial DNA sequence. However, levels of divergence based on nuclear markers have not been examined, and hence the potential for male-mediated gene flow between the species cannot be discounted. Moreover, little is known about population structure and migration patterns in either species. Here, we describe the use of microsatellites to investigate nuclear DNA differentiation between, and the pattern of population genetic structure within, the two cryptic pipistrelle species. In total, 1300 individuals from 82 maternity colonies were sampled across the British Isles and Continental Europe. We show, using multivariate analyses, that colonies of the same species are generally genetically more similar to each other than to those from the other species regardless of geographical location. Our findings support the hypothesis that the species are reproductively isolated. Significant patterns of genetic isolation by distance were identified in both species, indicating that mating may occur before any long-distance autumnal migration. The presence of a sea channel does not confer higher levels of genetic differentiation among colonies over and above distance alone in either species. Differences in genetic population structure were identified between the species, with P. pipistrellus showing a wider range of levels of genetic differentiation among colonies and a stronger relationship between genetic and geographical distance than P. pygmaeus. Differences in dispersal, mating behaviour, colony size and/or postglacial colonization patterns could contribute to the differences observed.

HISTORICAL ISOLATION, RANGE EXPANSION, AND SECONDARY CONTACT OF TWO HIGHLY DIVERGENT MITOCHONDRIAL LINEAGES IN SPOTTED SALAMANDERS (AMBYSTOMA MACULATUM)

The high species diversity of aquatic and terrestrial faunas in eastern North America has been attributed to range reductions and allopatric diversification resulting from historical climate change. The role these processes may have played in speciation is still a matter of considerable debate; however, their impacts on intraspecific genetic structure have been well documented. We use mitochondrial DNA sequences to reconstruct an intraspecific phylogeny of the widespread North American spotted salamander, Ambystoma maculatum, and test whether phylogenetic patterns conform to regional biogeographical hypotheses about the origins of diversity in eastern North America. Specifically, we address the number and locations of historical refugia, the extent and patterns of postglacial colonization by divergent lineages, and the origin and affinities of populations in the Interior Highland region. Despite apparent morphological uniformity, genetic discontinuities throughout the range of this species suggest that populations were historically fragmented in at least two refugia in the southern Appalachian Mountains. The ranges of these two highly divergent clades expanded northward, resulting in two widely distributed lineages that are sympatric in regions previously proposed as suture zones for other taxa. The evolutionary history of spotted salamander populations underscores the generality of biogeographical processes in eastern North America: despite differences in population size, glacial refugia, and vagility, similar signatures of differentiation are evident among and within widespread taxa.

Phylogeographic history of the land snail Candidula unifasciata (Helicellinae, Stylommatophora): fragmentation, corridor migration, and secondary contact.

We studied sequence variation in 16S rDNA in 204 individuals from 37 populations of the land snail Candidula unifasciata (Poiret 1801) across the core species range in France, Switzerland, and Germany. Phylogeographic, nested clade, and coalescence analyses were used to elucidate the species evolutionary history. The study revealed the presence of two major evolutionary lineages that evolved in separate refuges in southeast France as result of previous fragmentation during the Pleistocene. Applying a recent extension of the nested clade analysis (Templeton 2001), we inferred that range expansions along river valleys in independent corridors to the north led eventually to a secondary contact zone of the major clades around the Geneva Basin. There is evidence supporting the idea that the formation of the secondary contact zone and the colonization of Germany might be postglacial events. The phylogeographic history inferred for C. unifasciata differs from general biogeographic patterns of postglacial colonization previously identified for other taxa, and it might represent a common model for species with restricted dispersal.

Microsatellite data resolve phylogeographic patterns in European grayling, Thymallus thymallus, Salmonidae.

The phylogeography of an endangered salmonid, European grayling (Thymallus thymallus), was studied based on analysis of 17 nuclear microsatellite DNA loci. In agreement with earlier mitochondrial DNA (mtDNA) studies, phylogenetic relationships of the populations suggested that northern Europe was colonized from two distinct Pleistocene refugia. Furthermore, microsatellites revealed highly supported grouping of mainland Swedish, Norwegian, Danish, German and Slovenian populations, suggesting that grayling from the northwestern and central Europe have descended from their southern conspecifics. The level of divergence between populations was substantial, even across short geographical distances. Although this was in part due to postglacial colonization patterns and contemporary barriers for gene flow, the high divergence estimates between hydrologically connected sampling locations implied efficient interpopulation reproductive isolation. Microsatellites revealed that the populations exhibited, on average, only 3.5 (+/-2.2) alleles per locus, indicating that T. thymallus has strikingly low levels of intrapopulation genetic diversity as compared with other freshwater fish species. Accordingly, as indicated by analysis of molecular variance (AMOVA), only 49.1-58.0% of the total grayling microsatellite diversity resided within populations. A latitudinal genetic diversity gradient, potentially resulting from glaciation-mediated founder events, was not evident. Alternatively, it is possible that grayling display limited dispersal behaviour/capability, leading to low long-term effective population sizes and, consequently, depauperate intrapopulation polymorphism. These findings have implications for conservation of T. thymallus. Importantly, they exemplify that microsatellites can be highly informative for intraspecific phylogeography studies dealing with substantial divergence scales.

PHYLOGEOGRAPHIC HISTORY OF THE LAND SNAIL CANDIDULA UNIFASCIATA (HELICELLINAE, STYLOMMATOPHORA): FRAGMENTATION, CORRIDOR MIGRATION, AND SECONDARY CONTACT

We studied sequence variation in 16S rDNA in 204 individuals from 37 populations of the land snail Candidula unifasciata (Poiret 1801) across the core species range in France, Switzerland, and Germany. Phylogeographic, nested clade, and coalescence analyses were used to elucidate the species evolutionary history. The study revealed the presence of two major evolutionary lineages that evolved in separate refuges in southeast France as result of previous fragmentation during the Pleistocene. Applying a recent extension of the nested clade analysis (Templeton 2001), we inferred that range expansions along river valleys in independent corridors to the north led eventually to a secondary contact zone of the major clades around the Geneva Basin. There is evidence supporting the idea that the formation of the secondary contact zone and the colonization of Germany might be postglacial events. The phylogeographic history inferred for C. unifasciata differs from general biogeographic patterns of postglacial colonization previously identified for other taxa, and it might represent a common model for species with restricted dispersal.

Phylogeography, hybridization and speciation

This Special Issue of Molecular Ecology contains a selection of papers from participants in the ‘Phylogeography, Hybridization and Speciation’ meeting held at the Centre Paul Langevin, Aussois, France in April 2000. The meeting was conceived as a 60th birthday present for Professor Godfrey Hewitt, of the University of East Anglia, Norwich, UK, to recognize his seminal contributions to these three interconnected fields. Many of those present, and many more who were not able to attend, owe a debt of gratitude to Godfrey. For his numerous former students and research assistants he has been, and continues to be, a friend and supporter as well as an academic leader. For those from around the world who know him only from conferences or from his publications, he is an inspiration. This is an exciting time for the subject area, largely because of the new opportunities made available by advances in molecular ecology. Papers in this issue show clearly how powerful these methods can be in elucidating historical relationships among populations and species, in tracing patterns of postglacial colonization, and in dissecting the genetic basis of phenotypic differentiation or reproductive isolation. However, more traditional studies retain an ability to provide insights into evolutionary problems, and this is also reflected in this Special Issue. As molecular approaches develop further and generate ever larger data sets, more sophisticated analyses are needed to provide the most robust tests of alternative hypotheses or to extract the maximum amount of information. This is an area where there is still much to be learned. A hallmark of Godfrey Hewitt’s work has always been the integration of diverse approaches. A full understanding of a complex issue such as speciation requires data from ecology, palaeoecology, systematics, cytogenetics, and evolutionary theory as well as molecular biology. We hope that the papers in this issue reflect this breadth of Godfrey’s interests and influence, and the excitement we felt at the meeting. Mike Ritchie and Roger Butlin greatly acknowledge the help of Loren Rieseberg and Harry Smith in offering to publish these papers in a Special Issue of Molecular Ecology and for their editorial help. Most of all, we are grateful to all the authors and referees for their efforts. The Genetical Society and the University of East Anglia provided financial help for the meeting.

Colonization history in Fennoscandian rodents

Fennoscandia probably constitutes one of the best places on earth to study faunal history. During the height of the most recent glacial period Fennoscandia was completely covered with ice. Thus, the majority of extant species must originate from ancestors who survived the latest glaciation in non-glaciated areas outside Fennoscandia. Moreover, the geography and geological history of Fennoscandia suggests that post-glacial recolonization by land mammals must have been restricted to specific routes in time and space. Phylogeographic surveys of mitochondrial DNA (mtDNA) variation in Fennoscandian rodents have demonstrated that glacial history and patterns of post-glacial colonization have played a major role in shaping present day patterns of genetic differentiation within species. Thus, the genetic imprints of historical demographic conditions and vicariant geographic events have been retained within species and can be used to infer the history of populations. The field vole (Microtus agrestis) is used to illustrate these data and processes. Comparisons are made with phylogeographic surveys of the bank vole (Clethrionomys glareolus), the eastern house mouse (Mus musculus) and the wood lemming (Myopus schisticolor) as well as a few other species for which less extensive studies have been performed. The main patterns of post-glacial colonization of Fennoscandia by rodents are described. The effects of timing and patterns of colonization on contemporary population genetic structure and levels of genetic variation are discussed. Specifically, the effects of hybridization and introgression as well as founder events and bottlenecks are explored.

Colonization history in Fennoscandian rodents

Fennoscandia probably constitutes one of the best places on earth to study faunal history. During the height of the most recent glacial period Fennoscandia was completely covered with ice. Thus, the majority of extant species must originate from ancestors who survived the latest glaciation in non-glaciated areas outside Fennoscandia. Moreover, the geography and geological history of Fennoscandia suggests that post-glacial recolonization by land mammals must have been restricted to specific routes in time and space. Phylogeographic surveys of mitochondrial DNA (mtDNA) variation in Fennoscandian rodents have demonstrated that glacial history and patterns of post-glacial colonization have played a major role in shaping present day patterns of genetic differentiation within species. Thus, the genetic imprints of historical demographic conditions and vicariant geographic events have been retained within species and can be used to infer the history of populations. The field vole (Microtus agrestis) is used to illustrate these data and processes. Comparisons are made with phylogeographic surveys of the bank vole (Clethrionomys glareolus), the eastern house mouse (Mus musculus) and the wood lemming (Myopus schisticolor) as well as a few other species for which less extensive studies have been performed. The main patterns of post-glacial colonization of Fennoscandia by rodents are described. The effects of timing and patterns of colonization on contemporary population genetic structure and levels of genetic variation are discussed. Specifically, the effects of hybridization and introgression as well as founder events and bottlenecks are explored.

Genetic Relationships of Even-Year Northwestern Alaskan Pink Salmon

Abstract Even-year cohorts of northwestern Alaskan pink salmon Oncorhynchus gorbuscha, sampled from 13 Aleutian islands, 1 Kodiak Island, and 4 eastern Bering Sea streams, were surveyed electrophoretically for 29 protein-coding loci. We observed no significant genetic heterogeneity among collections from the Aleutian Islands or within the Bering Sea regions of Bristol Bay and Norton Sound. The Bering Sea and Aleutian Island populations were more closely related to each other than to the Kodiak Island population. This similarity may reflect patterns of post-glacial colonization from the Bering Refuge. Genetic comparisons of northwestern Alaskan pink salmon with Asian populations from Sakhalin Island suggest that the Asian fish are most closely related to the northernmost North American populations that we collected, i.e., those of Norton Sound. Homogeneity among Aleutian Island populations is notable because the islands extend nearly 1,000 km, a distance over which pink salmon populations in other regions ...