Genetic variation and effective population size in isolated populations of coastal cutthroat

Abstract Following glacial recession in southeast Alaska, waterfalls created by isostatic rebound have isolated numerous replicate populations of coastal cutthroat trout (Oncorhynchus clarkii clarkii) in short coastal streams. These replicate isolated populations offer an unusual opportunity to examine factors associated with the maintenance of genetic diversity. We used eight microsatellites to examine genetic variation within and differentiation among 12 population pairs sampled from above and below these natural migration barriers. Geological evidence indicated that the above-barrier populations have been isolated for 8,000-12,500 years. Genetic differentiation among below-barrier populations (F ST = 0.10, 95% C.I. 0.08-0.12) was similar to a previous study of more southern populations of this species. Above-barrier populations were highly differentiated from adjacent below-barrier populations (mean pairwise F ST = 0.28; SD 0.18) and multiple lines of evidence were consistent with asymmetric downstream gene flow that varied among streams. Each above-barrier population had reduced within-population genetic variation when compared to the adjacent belowbarrier population. Within-population genetic diversity was significantly correlated with the amount of available habitat in above-barrier sites. Increased genetic differentiation of above-barrier populations with lower genetic diversity suggests that genetic drift has been the primary cause of genetic divergence. Long-term estimates of N e based on loss of heterozygosity over the time since isolation were large (3,170; range 1,077-7,606) and established an upper limit for N e if drift were the only evolutionary process responsible for loss of genetic diversity. However, it is likely that a combination of mutation, selection, and gene flow have also contributed to the genetic diversity of above-barrier populations. Contemporary above-barrier N e estimates were much smaller than long-term N e estimates, not correlated with withinpopulation genetic diversity, and not consistent with the amount of genetic variation retained, given the approximate 10,000-year period of isolation. The populations isolated by waterfalls in this study that occur in larger stream networks have retained substantial genetic variation, which suggests that the amount of habitat in headwater streams is an important consideration for maintaining the evolutionary potential of isolated populations

Alaskan coho salmon genotypes

Genotype data from nine microsatellite loci for 2584 coho salmon in 32 locations in Alaska. This data file is formatted for use in the computer program GenePop v4.0. The genotypes in this file have NOT been standardized with other laboratories -- see readme file for further information

Data from: Patterns of intra- and inter-population genetic diversity in Alaskan coho salmon: implications for conservation

Little is known about the genetic diversity of coho salmon in Alaska, although this area represents half of the species’ North American range. In this study, nine microsatellite loci were used to genotype 32 putative coho salmon populations from seven regions of Alaska. The primary objectives were to estimate and evaluate the degree and spatial distribution of neutral genetic diversity within and among populations of Alaskan coho salmon. Genetic analysis yielded four results that provide insight into forces influencing genetic diversity in Alaskan coho salmon and have important conservation implications: 1) significant population differentiation was found within each region; 2) the degree of differentiation (FST = 0.099) among populations was as large or larger than that reported for other Pacific salmon species in Alaska; 3) phenetic clustering of populations showed weak geographic concordance; 4) strong genetic isolation by distance was only apparent at the finest geographic scale (within a drainage). These results suggest that coho salmon populations are small relative to populations of other Pacific salmon, and the genetic diversity within and among coho salmon populations is influenced primarily by genetic drift, and not gene flow. Resource management and conservation actions affecting coho salmon in Alaska must recognize that the populations are generally small, isolated, and probably exhibit local adaptation to different spawning and freshwater rearing habitats. These factors justify managing and conserving Alaskan coho salmon at a fine geographic scale

Data from: The time of origin and genetic diversity of three isolated Kokanee populations in southwest Alaska

We examined the time of origin and genetic diversity of native kokanee, the nonanadromous ecotype of Sockeye Salmon Oncorhynchus nerka, from three isolated lakes in the Katmai National Park and Preserve in southwest Alaska. These kokanee evolved independently from Sockeye Salmon when migration barriers arose, blocking ocean access. We used information about the relative age of each barrier to hypothesize the relative time of origin for kokanee in each lake. In addition, we used data from 13 microsatellite loci to test our time of origin hypotheses and assess genetic diversity of kokanee from these three lakes and proximate Sockeye Salmon populations. Coalescent-based estimates of the time of origin for kokanee in Jo-Jo Lake (170 years before present [ybp]) and Devil’s Cove Lake (6,583 ybp) were consistent with the relative age of barriers isolating each lake. However, data from Dakavak Lake (1,379 ybp) suggested that the barrier was older than hypothesized. Indices of intrapopulation diversity were lower for kokanee than for Sockeye Salmon. Estimates for kokanee population divergence (RST; the FST analog for microsatellites) among the three lakes were consistent with time of origin estimates. Furthermore, the most recently isolated kokanee (Jo-Jo Lake population) were most closely related to neighboring Sockeye Salmon. Only the kokanee from Jo-Jo Lake exhibited a relatively low historical effective population size (Ne ≈ 107) and evidence of a genetic bottleneck. Taken together, the results of this study show that although rare, kokanee in Alaska are not ephemeral and can persist in isolation for hundreds of generations despite the colder temperatures and shorter growing season, that are thought to limit their sustainability in Alaska

Data from: Comparative landscape genetic analysis of three Pacific salmon species from subarctic North America

We examined the assumption that landscape heterogeneity similarly influences the spatial distribution of genetic diversity in closely related and geographically overlapping species. Accordingly, we evaluated the influence of watershed affiliation and nine habitat variables from four categories (spatial isolation, habitat size, climate, and ecology) on population divergence in three species of Pacific salmon (Oncorhynchus tshawytscha, O. kisutch, and O. keta) from three contiguous watersheds in subarctic North America. By incorporating spatial data we found that the three watersheds did not form the first level of hierarchical population structure as predicted. Instead, each species exhibited a broadly similar spatial pattern: a single coastal group with populations from all watersheds and one or more inland groups primarily in the largest watershed. These results imply that the spatial scale of conservation should extend across watersheds rather than at the watershed level which is the scale for fishery management. Three independent methods of multivariate analysis identified two variables as having influence on population divergence across all watersheds: precipitation in all species and subbasin area (SBA) in Chinook. Although we found general broad-scale congruence in the spatial patterns of population divergence and evidence that precipitation may influence population divergence in each species, we also found differences in the level of population divergence (coho > Chinook and chum) and evidence that SBA may influence population divergence only in Chinook. These differences among species support a species-specific approach to evaluating and planning for the influence of broad-scale impacts such as climate change

Data from: Comparative landscape genetic analysis of three Pacific salmon species from subarctic North America

We examined the assumption that landscape heterogeneity similarly influences the spatial distribution of genetic diversity in closely related and geographically overlapping species. Accordingly, we evaluated the influence of watershed affiliation and nine habitat variables from four categories (spatial isolation, habitat size, climate, and ecology) on population divergence in three species of Pacific salmon (Oncorhynchus tshawytscha, O. kisutch, and O. keta) from three contiguous watersheds in subarctic North America. By incorporating spatial data we found that the three watersheds did not form the first level of hierarchical population structure as predicted. Instead, each species exhibited a broadly similar spatial pattern: a single coastal group with populations from all watersheds and one or more inland groups primarily in the largest watershed. These results imply that the spatial scale of conservation should extend across watersheds rather than at the watershed level which is the scale for fishery management. Three independent methods of multivariate analysis identified two variables as having influence on population divergence across all watersheds: precipitation in all species and subbasin area (SBA) in Chinook. Although we found general broad-scale congruence in the spatial patterns of population divergence and evidence that precipitation may influence population divergence in each species, we also found differences in the level of population divergence (coho > Chinook and chum) and evidence that SBA may influence population divergence only in Chinook. These differences among species support a species-specific approach to evaluating and planning for the influence of broad-scale impacts such as climate change

Microsatellite genotypes for fountain darters

Genotype data from 23 microsatellite loci used to evaluate genetic diversity in 327 fountain darters (E. fonticola) from 16 sample locations in the Comal (CR) and San Marcos (SMR) rivers, Guadalupe River Basin, Texas, USA. The genotype data is formatted for use in the computer program FSTAT

Table 1

Location, site abbreviation (Abbr), sample year, sample size (n), and life stage (A = adult, J = juvenile) of fish sampled from 32 putative coho salmon populations in seven regions of Alaska

Data from: Genetic diversity and divergence in the fountain darter (Etheostoma fonticola): implications for conservation of an endangered species

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