DISCORDANT DISTRIBUTION OF POPULATIONS AND GENETIC VARIATION IN A SEA STAR WITH HIGH DISPERSAL POTENTIAL

Patiria miniata, a broadcast‐spawning sea star species with high dispersal potential, has a geographic range in the intertidal zone of the northeast Pacific Ocean from Alaska to California that is characterized by a large range gap in Washington and Oregon. We analyzed spatial genetic variation across the P. miniata range using multilocus sequence data (mtDNA, nuclear introns) and multilocus genotype data (microsatellites). We found a strong phylogeographic break at Queen Charlotte Sound in British Columbia that was not in the location predicted by the geographical distribution of the populations. However, this population genetic discontinuity does correspond to previously described phylogeographic breaks in other species. Northern populations from Alaska and Haida Gwaii were strongly differentiated from all southern populations from Vancouver Island and California. Populations from Vancouver Island and California were undifferentiated with evidence of high gene flow or very recent separation across the range disjunction between them. The surprising and discordant spatial distribution of populations and alleles suggests that historical vicariance (possibly caused by glaciations) and contemporary dispersal barriers (possibly caused by oceanographic conditions) both shape population genetic structure in this species.     

Host and geographic range extensions of the North American strain of viral hemorrhagic septicemia virus

Viral hemorrhagic septicemia virus (VHSV) was isolated from populations of Pacific sardine Sardinops sagax from the coastal waters of Vancouver Island, British Columbia, Canada, and central and southern California, USA. The virus was also isolated from Pacific mackerel Scomber japonicus in southern California, from eulachon or smelt Thaleichthys pacificus, and surf smelt Hypomesus pretiosus pretiosus from Oregon, USA. Mortality and skin lesions typical of viral hemorrhagic septicemia in other marine fish species were observed among sardine in Canada and in a few surf smelt from Oregon, but the remaining isolates of VHSV were obtained from healthy appearing fish. The prevalence of VHSV among groups of apparently healthy sardine, mackerel and smelt ranged from 4 to 8%, in California and Oregon. A greater prevalence of infection (58%) occurred in groups of sardine sampled in Canada that sustained a naturally occurring epidemic during 1998-99. A captive group of surf smelt in Oregon exhibited an 81% prevalence of infection with clinical signs in only a few fish. The new isolates were confirmed as North American VHSV and were closely related based on comparisons of the partial nucleotide sequence of the glycoprotein (G) gene. The VHSV isolates from sardine in Canada and California were the most closely related, differing from isolates obtained from other marine fish species and salmonids in British Columbia, Canada, Alaska and Washington, USA. These new virus isolations extend both the known hosts (sardine, mackerel and 2 species of smelt) and geographic range (Oregon and California, USA) of VHSV.     

Hierarchical structure of mitochondrial DNA gene flow among humpback whales Megaptera novaeangliae, world-wide

The genetic structure of humpback whale populations and subpopulation divisions is described by restriction fragment length analysis of the mitochondrial (mt) DNA from samples of 230 whales collected by biopsy darting in 11 seasonal habitats representing six subpopulations, or 'stocks', world-wide. The hierarchical structure of mtDNA haplotype diversity among population subdivisions is described using the analysis of molecular variance (AMOVA) procedure, the analysis of gene identity, and the genealogical relationship of haplotypes as constructed by parsimony analysis and distance clustering. These analyses revealed: (i) significant partitioning of world-wide genetic variation among oceanic populations, among subpopulations or 'stocks' within oceanic populations and among seasonal habitats within stocks; (ii) fixed categorical segregation of haplotypes on the south-eastern Alaska and central California feeding grounds of the North Pacific; (iii) support for the division of the North Pacific population into a central stock which feeds in Alaska and winters in Hawaii, and an eastern or 'American' stock which feeds along the coast of California and winters near Mexico; (iv) evidence of genetic heterogeneity within the Gulf of Maine feeding grounds and among the sampled feeding and breeding grounds of the western North Atlantic; and (v) support for the historical division between the Group IV (Western Australia) and Group V (eastern Australia, New Zealand and Tonga) stocks in the Southern Oceans. Overall, our results demonstrate a striking degree of genetic structure both within and between oceanic populations of humpback whales, despite the nearly unlimited migratory potential of this species. We suggest that the humpback whale is a suitable demographic and genetic model for the management of less tractable species of baleen whales and for the general study of gene flow among long-lived, mobile vertebrates in the marine ecosystem.     

Fine-scale population genetic structure in Alaskan Pacific halibut (<Emphasis Type="Italic">Hippoglossus stenolepis</Emphasis>)

Pacific halibut collected in the Aleutian Islands, Bering Sea and Gulf of Alaska were used to test the hypothesis of genetic panmixia for this species in Alaskan marine waters. Nine microsatellite loci and sequence data from the mitochondrial (mtDNA) control region were analyzed. Eighteen unique mtDNA haplotypes were found with no evidence of geographic population structure. Using nine microsatellite loci, significant heterogeneity was detected between Aleutian Island Pacific halibut and fish from the other two regions (F _ST range = 0.007–0.008). Significant F _ST values represent the first genetic evidence of divergent groups of halibut in the central and western Aleutian Archipelago. No significant genetic differences were found between Pacific halibut in the Gulf of Alaska and the Bering Sea leading to questions about factors contributing to separation of Aleutian halibut. Previous studies have reported Aleutian oceanographic conditions at deep inter-island passes leading to ecological discontinuity and unique community structure east and west of Aleutian passes. Aleutian Pacific halibut genetic structure may result from oceanographic transport mechanisms acting as partial barriers to gene flow with fish from other Alaskan waters.     

Population genetic structure of annual and perennial populations of Zostera marina L. along the Pacific coast of Baja California and the Gulf of California

The Baja California peninsula represents a biogeographical boundary contributing to regional differentiation among populations of marine animals. We investigated the genetic characteristics of perennial and annual populations of the marine angiosperm, Zostera marina, along the Pacific coast of Baja California and in the Gulf of California, respectively. Populations of Z. marina from five coastal lagoons along the Pacific coast and four sites in the Gulf of California were studied using nine microsatellite loci. Analyses of variance revealed significant interregional differentiation, but no subregional differentiation. Significant spatial differentiation, assessed using θ_ST values, was observed among all populations within the two regions. Z. marina populations along the Pacific coast are separated by more than 220 km and had the greatest θ_ST (0.13–0.28) values, suggesting restricted gene flow. In contrast, lower but still significant genetic differentiation was observed among populations within the Gulf of California (θ_ST = 0.04–0.18), even though populations are separated by more than 250 km. This suggests higher levels of gene flow among Gulf of California populations relative to Pacific coast populations. Direction of gene flow was predominantly southward among Pacific coast populations, whereas no dominant polarity in the Gulf of California populations was observed. The test for isolation by distance (IBD) showed a significant correlation between genetic and geographical distances in Gulf of California populations, but not in Pacific coast populations, perhaps because of shifts in currents during El Niño Southern Oscillation (ENSO) events along the Pacific coast.     

22 Nutrient use efficiency and coastal productivity: comparative perspectives on ecosystem structure and mechanisms of control

Net primary production in marine ecosystems ultimately reflects the inputs of nutrients and the efficiency with which nutrients are acquired and used by phytoplankton in growth. In contrast to our understanding of the linkages between nutrient loading and production, the influence of nutrient use efficiency (NUE) on cross-system variations in coastal productivity remains unclear. Nutrient use efficiency at the ecosystem scale is the product of the per capita efficiency of nutrient use in phytoplankton growth and the efficiency with which phytoplankton communities are able to assimilate limiting nutrient(s). We measured the relative dominance of ecosystem N pools by phytoplankton biomass as an index of NUE across 56 inner-shelf sites. These sites were distributed across a strong geographic range of upwelling intensity and productivity along the coasts of Oregon, California and New Zealand. We also compiled an extensive dataset of published NUE values in coastal and oceanic sites in order to assess cross-system patterns and differences in NUE. Our results indicate that exceptional rates of productivity in inner-shelf upwelling systems arise as a consequence of near dominance of ecosystem N pools by phytoplankton biomass. Elevated rates of NUE nevertheless appear to be a transient phenomenon in marine systems. Cross-shelf transects across upwelling fronts off the Oregon coast reveal a temporal pattern of intense phytoplankton blooms and decline that reflects the eventual dominance of ecosystems N pools by detrital and dissolved organic N pools. Our findings suggest that NUE may play a central role in governing the productivity of marine ecosystems.     

SPECIATION AND POPULATION GENETIC STRUCTURE IN TROPICAL PACIFIC SEA URCHINS

Unlike populations of many terrestrial species, marine populations often are not separated by obvious, permanent barriers to gene flow. When species have high dispersal potential and few barriers to gene flow, allopatric divergence is slow. Nevertheless, many marine species are of recent origin, even in taxa with high dispersal potential. To understand the relationship between genetic structure and recent species formation in high dispersal taxa, we examined population genetic structure among four species of sea urchins in the tropical Indo-West Pacific that have speciated within the past one to three million years. Despite high potential for gene flow, mtDNA sequence variation among 200 individuals of four species in the urchin genus Echinometra shows a signal of strong geographic effects. These effects include (1) substantial population heterogeneity; (2) lower genetic variation in peripheral populations; and (3) isolation by distance. These geographic patterns are especially strong across scales of 5000-10,000 km, and are weaker over scales of 2500-5000 km. As a result, strong geographic patterns would not have been readily visible except over the wide expanse of the tropical Pacific. Surface currents in the Pacific do not explain patterns of gene flow any better than do patterns of simple spatial proximity. Finally, populations of each species tend to group into large mtDNA regions with similar mtDNA haplotypes, but these regional boundaries are not concordant in different species. These results show that all four species have accumulated mtDNA differences over similar spatial and temporal scales but that the precise geographic pattern of genetic differentiation varies for each species. These geographic patterns appear much less deterministic than in other well-known coastal marine systems and may be driven by chance and historical accident.     

A signal for independent coastal and continental histories among North American wolves

Relatively little genetic variation has been uncovered in surveys across North American wolf populations. Pacific Northwest coastal wolves, in particular, have never been analysed. With an emphasis on coastal Alaska wolf populations, variation at 11 microsatellite loci was assessed. Coastal wolf populations were distinctive from continental wolves and high levels of diversity were found within this isolated and relatively small geographical region. Significant genetic structure within southeast Alaska relative to other populations in the Pacific Northwest, and lack of significant correlation between genetic and geographical distances suggest that differentiation of southeast Alaska wolves may be caused by barriers to gene flow, rather than isolation by distance. Morphological research also suggests that coastal wolves differ from continental populations. A series of studies of other mammals in the region also has uncovered distinctive evolutionary histories and high levels of endemism along the Pacific coast. Divergence of these coastal wolves is consistent with the unique phylogeographical history of the biota of this region and re-emphasizes the need for continued exploration of this biota to lay a framework for thoughtful management of southeast Alaska.     

Eco-Evolutionary Processes Generating Diversity Among Bottlenose Dolphin, <Emphasis Type="Italic">Tursiops truncatus</Emphasis>, Populations off Baja California,Mexico

For highly mobile species that nevertheless show fine-scale patterns of population genetic structure, the relevant evolutionary mechanisms determining structure remain poorly understood. The bottlenose dolphin (Tursiops truncatus) is one such species, exhibiting complex patterns of genetic structure associated with local habitat dependence in various geographic regions. Here we studied bottlenose dolphin populations in the Gulf of California and Pacific Ocean off Baja California where habitat is highly structured to test associations between ecology, habitat dependence and genetic differentiation. We investigated population structure at a fine geographic scale using both stable isotope analysis (to assess feeding ecology) and molecular genetic markers (to assess population structure). Our results show that there are at least two factors affecting population structure for both genetics and feeding ecology (as indicated by stable isotope profiles). On the one hand there is a signal for the differentiation of individuals by ecotype, one foraging more offshore than the other. At the same time, there is differentiation between the Gulf of California and the west coast of Baja California, meaning that for example, nearshore ecotypes were both genetically and isotopically differentiated either side of the peninsula. We discuss these data in the context of similar studies showing fine-scale population structure for delphinid species in coastal waters, and consider possible evolutionary mechanisms.     

Multilocus phylogeography of the sea snake Hydrophis curtus reveals historical vicariance and cryptic lineage diversity

The Indo‐Australian archipelago (IAA) supports the world's highest diversity of marine fish, invertebrates and reptiles. Many of the marine fish and invertebrates show congruent phylogeographic patterns, supporting a view that the region's complex geo‐climatic history has played an important role in generating its exceptional biodiversity. Here, we examine population genetic structure of the viviparous sea snake, Hydrophis curtus, to assess how past and present barriers to gene flow in the IAA have contributed to genetic and species diversity in a fully marine reptile. Mitochondrial and anonymous nuclear sequences and ten microsatellite loci were used to identify patterns of historical genetic structure and population expansion, reconstruct dated genealogies and assess levels of recent gene flow. These markers revealed strong concordant geographic structure within H. curtus with a prominent genetic break between populations broadly distributed in the Indian Ocean and the West Pacific. These populations were estimated to have diverged in the late Pliocene or early Pleistocene, and microsatellite admixture analyses suggested limited recent gene flow between them despite the current lack of barriers to dispersal, indicating possible cryptic species. Subsequent divergence in the mid–late Pleistocene was detected within the West Pacific clade among the populations in the Phuket‐Thailand region, South‐East Asia and Australia, and two of these populations also showed genetic signals of recent range expansions. Our results show that climatic fluctuations during the Plio‐Pleistocene generated high levels of cryptic genetic diversity in H. curtus, and add to similar findings for diverse other marine groups in the IAA.     

Nearshore subtidal community structure compared between inner coast and outer coast sites in Southeast Alaska

Processes that structure subarctic marine communities, particularly in glaciated regions, are not well understood. This understanding is needed as a baseline and to manage these communities in the face of future climate-driven changes. This study investigates two coastal regions of Southeast Alaska with the goals to (a) identify and compare patterns of subtidal community structure for macroalgal, fish, macroinvertebrate (>5?cm), and small epibenthic invertebrate (<5?cm) communities between inner coast and outer coast sites and (b) link patterns of community structure to habitat and environmental parameters. Species assemblage and benthic habitat data were used to compare species diversity and community composition at 6?m and 12?m depths at nine inner coast and nine outer coast sites. Multivariate analysis was applied to reduce environmental variables to major gradients, to resolve community structure, and to relate community structure to habitat and environmental variables. Increased salinity and decreased temperature at outer coast sites compared with inner coast sites were associated with community structure, with greater species diversity at outer coast sites at 6?m depth. Invertebrate community composition was associated with benthic habitat, including crust and coralline algae for macroinvertebrates, and algal cover and substrate for small epibenthic invertebrates. This research suggests that marine communities in glaciated regions are strongly influenced by freshwater input and that future climate-driven changes in freshwater input will likely result in marine community composition changes.     

Genetic signature of recent glaciation on populations of a near-shore marine fish species (Syngnathus leptorhynchus)

Continental glaciation has played a major role in shaping the present-day phylogeography of freshwater and terrestrial species in the Northern Hemisphere. Recent work suggests that coastal glaciation during ice ages may have also had a significant impact on marine species. The bay pipefish, Syngnathus leptorhynchus , is a near-shore Pacific coast fish species with an exceptionally wide latitudinal distribution, ranging from Bahia Santa Maria, Baja California to Prince William Sound, Alaska. Survey data indicate that S. leptorhynchus is experiencing a range expansion at the northern limit of its range, consistent with colonization from southern populations. The present study uses six novel microsatellite markers and mitochondrial DNA (mtDNA) sequence data to study the present-day population genetic structure of four coastal populations of S. leptorhynchus . Deficits in mtDNA and nuclear DNA diversity in northern populations from regions glaciated during the last glacial maximum (LGM) [ c . 18 000 years before present ( bp )] suggest that these populations were effected by glacial events. Direct estimates of population divergence times derived from both isolation and isolation-with-migration models of evolution are also consistent with a postglacial phylogenetic history of populations north of the LGM. Sequence data further indicate that a population at the southern end of the species range has been separated from the three northern populations since long before the last interglacial event ( c . 130 000 years bp ), suggesting that topographical features along the Pacific coast may maintain population separation in regions unimpacted by coastal glaciation.     

Genetic diversity, structure, and demographic change in tanoak, Lithocarpus densiflorus (Fagaceae), the most susceptible species to sudden oak death in California

Knowledge of population genetic structure of tanoak (Lithocarpus densiflorus) is of interest to pathologists seeking natural variation in resistance to sudden oak death disease, to resource managers who need indications of conservation priorities in this species now threatened by the introduced pathogen (Phytophthora ramorum), and to biologists with interests in demographic processes that have shaped plant populations. We investigated population genetic structure using nuclear and chloroplast DNA (cpDNA) and inferred the effects of past population demographic processes and contemporary gene flow. Our cpDNA results revealed a strong pattern of differentiation of four regional groups (coastal California, southern Oregon, Klamath mountains, and Sierra Nevada). The chloroplast haplotype phylogeny suggests relatively deep divergence of Sierra Nevada and Klamath populations from those of coastal California and southern Oregon. A widespread coastal California haplotype may have resulted from multiple refugial sites during the Last Glacial Maximum or from rapid recolonization from few refugia. Analysis of nuclear microsatellites suggests two major groups: (1) central coastal California and (2) Sierra Nevada/Klamath/southern Oregon and an area of admixture in north coastal California. The low level of nuclear differentiation is likely to be due to pollen gene flow among populations during postglacial range expansion.     

Phenotypic variation among populations of Atherinops affinis(Atherinopsidae) with insights from a geometric morphometric analysis

Morphological character variation was examined in Atherinops affinis , a temperate marine silverside with a broad geographic range and presumed limited powers of dispersal. Populations of this species were sampled from three California mainland sites, one Channel Island site and one site in the upper Gulf of California. A geometric morphometric analysis yielded higher resolution in the assessment of phenotypic divergence among the four Pacific coast populations than either body measurement or meristic analysis, and it showed that most of the shape variation among these populations occurs in the head region and body depth of the fish. All three analyses supported the hypothesis that populations of A. affinis from central and southern California coastal waters and from Santa Catalina Island are morphologically distinct from each other; the Santa Catalina Island population was found to be the most divergent. On the basis of meristic characters alone, the population of A. affinis from the upper Gulf of California was different from A. affinis populations along the Pacific coast of California. The analyses revealed variation in several morphological characters, e.g . body depth and meristics, known to vary in association with environmental conditions. Given that A. affinis appears to have low among‐population genetic variation, this species may be phenotypically plastic in response to the environmental conditions of the habitat of each population.     

Phylogeography and spatial genetic structure of the Southern torrent salamander: implications for conservation and management

The Southern torrent salamander (Rhyacotriton variegatus) was recently found not warranted for listing under the US Endangered Species Act due to lack of information regarding population fragmentation and gene flow. Found in small-order streams associated with late-successional coniferous forests of the US Pacific Northwest, threats to their persistence include disturbance related to timber harvest activities. We conducted a study of genetic diversity throughout this species' range to 1) identify major phylogenetic lineages and phylogeographic barriers and 2) elucidate regional patterns of population genetic and spatial phylogeographic structure. Cytochrome b sequence variation was examined for 189 individuals from 72 localities. We identified 3 major lineages corresponding to nonoverlapping geographic regions: a northern California clade, a central Oregon clade, and a northern Oregon clade. The Yaquina River may be a phylogeographic barrier between the northern Oregon and central Oregon clades, whereas the Smith River in northern California appears to correspond to the discontinuity between the central Oregon and northern California clades. Spatial analyses of genetic variation within regions encompassing major clades indicated that the extent of genetic structure is comparable among regions. We discuss our results in the context of conservation efforts for Southern torrent salamanders.     

INTERCHANGE AND ISOLATION OF HUMPBACK WHALES OFF CALIFORNIA AND OTHER NORTH PACIFIC FEEDING GROUNDS

Humpback whales feed in several high-latitude areas of the North Pacific. We examined the interchange of humpback whales between one of these areas, off California, and those in other feeding grounds in the eastern North Pacific:. Fluke photographs of 597 humpback whales identified off California between 1986 and 1992 were compared with those off Oregon and Washington (29); British Columbia (81); southeastern Alaska (343); Prince William Sound, Alaska (141); Kodiak Island, Alaska (104); Shumagin Islands, Alaska (22); and in the Bering Sea (7). A high degree of interchange, both inter-and intrayear, was found among humpback whales seen off California, Oregon, and Washington., A low rate of interchange was found between British Columbia and California.: two whales seen near the British Columbia/Washington border were photographed off California in a different year, No interchange was found between California and the three feeding areas in Alaska. Humpback whales off California, Oregon, and Washington form a single intermixing feeding aggregation with only limited interchange with areas farther north. These findings are consistent with photographic identification studies in the North Atlantic and with genetic studies in both the North Atlantic and North Pacific.     

Streaked horned lark <Emphasis Type="Italic">Eremophila alpestris strigata</Emphasis> has distinct mitochondrial DNA

The Streaked Horned Lark (STHL; Eremophila alpestris strigata) is a federal candidate for listing under the Endangered Species Act. We evaluated the conservation status and level of genetic diversity of the STHL using the complete mitochondrial ND2 gene. We sampled 32 STHLs from the southern Puget Sound region, the Pacific coast, and Whites Island in the Columbia River of Washington, and additional 68 horned larks from Alaska, alpine and eastern Washington, Oregon, California, and Asia (outgroups). Our Maximum Likelihood analysis of 32 haplotypes identified three geographically concordant clades in Pacific coast states: Pacific Northwest (alpine and eastern Washington, Alaska), Pacific Coast (western Washington, California), and Great Basin (eastern Oregon). Each of the three clades was supported by bootstrap values ≥86%. The distance among them varied from 0.72 to 0.79% nucleotide divergence excluding intraclade variation. The relationship among the clades was not resolved. AMOVA also showed significant structuring of haplotypes among the three clades. Differences among clades accounted for 75.7% of sequence variation, differences among localities within clades accounted for 12.1%, and differences among individuals within localities accounted for the remaining 12.2%. Although STHL populations were closely related to the Californian sample, they appeared unique and isolated. All pairwise F _st values involving the STHL samples were significant (except between themselves). STHLs appear to have remarkably low genetic diversity; all 32 STHLs shared the same haplotype. Even with small sample sizes, all other localities had multiple haplotypes. Because the STHL appears to be unique and isolated, and to have little genetic diversity our data suggest it should be a conservation priority.     

Gene flow in the anemone Anthopleura elegantissima limits signatures of local adaptation across an extensive geographic range

Species inhabiting marine environments face a wide range of environmental conditions that vary spatially across several orders of magnitude. The selective pressures that these conditions impose on marine organisms, in combination with potentially high rates of gene flow between distant populations, make it difficult to predict the extent to which these populations can locally adapt. Here, I identify how selection and gene flow influence the population genetic structure of the anemone Anthopleura elegantissima along the Pacific coast of North America. Isolation by distance is the dominant pattern across the range of this species, with a genetic break near Pt. Conception, CA. Furthermore, demographic modelling suggests that this species was historically confined to southerly latitudes before expanding northward. Outlier analyses identify 24 loci under selection (out of ~1,100), but the same analysis on simulated genetic data generated using the most likely demographic model erroneously identified the same number of loci under selection, if not more. Taken together, these results suggest that demographic processes are the dominant force shaping population genetic patterns in A. elegantissima along the Pacific coast of North America. I discuss these patterns in terms of the evolutionary history of A. elegantissima, the potential for local adaptation, and their consequences with respect to interactions with the endosymbiont Breviolum muscatinei across their geographic range.     

Patterns of Mass Mortality among Rocky Shore Invertebrates across 100 km of Northeastern Pacific Coastline

Mass mortalities in natural populations, particularly those that leave few survivors over large spatial areas, may cause long-term ecological perturbations. Yet mass mortalities may remain undocumented or poorly described due to challenges in responding rapidly to unforeseen events, scarcity of baseline data, and difficulties in quantifying rare or patchily distributed species, especially in remote or marine systems. Better chronicling the geographic pattern and intensity of mass mortalities is especially critical in the face of global changes predicted to alter regional disturbance regimes. Here, we couple replicated post-mortality surveys with preceding long-term surveys and historical data to describe a rapid and severe mass mortality of rocky shore invertebrates along the north-central California coast of the northeastern Pacific Ocean. In late August 2011, formerly abundant intertidal populations of the purple sea urchin (Strongylocentrotus purpuratus, a well-known ecosystem engineer), and the predatory six-armed sea star (Leptasterias sp.) were functionally extirpated from ~100 km of coastline. Other invertebrates, including the gumboot chiton (Cryptochiton stelleri) the ochre sea star (Pisaster ochraceus), and subtidal populations of purple sea urchins also exhibited elevated mortality. The pattern and extent of mortality suggest the potential for long-term population, community, and ecosystem consequences, recovery from which may depend on the different dispersal abilities of the affected species.     

Glacial biogeography of North American coho salmon (Oncorhynchus kisutch)

To study the glacial biogeography of coho we examined 20 microsatellite loci and mitochondrial DNA D-loop sequence in samples from Alaska to California. Microsatellite data divided our samples among five biogeographic regions: (1) Alaska and northern coastal British Columbia; (2) the Queen Charlotte Islands; (3) the mainland coast of British Columbia and northern Washington State; (4) the Thompson River; and (5) Oregon and California. The D-loop sequence data suggested three geographical regions: (1) Oregon and California; (2) the Thompson River; and (3) all the other sites north of the southern ice margin. Microsatellite data revealed no difference in the number of alleles in different regions, but mitochondrial DNA data revealed a cline of decreasing diversity from south to north. We suggest that the two signals presented by these different marker types illuminate two time frames in the history of this species. Endemic microsatellite diversity in Alaska and on the Queen Charlotte Islands provides evidence in favour of Fraser Glaciation refugia in these regions. The loss of mitochondrial variation from south to north suggests that one of the earlier, more extensive, Pleistocene glaciations eliminated coho from its northern range.