Taylor E B, Stamford M D, Baxter J S
Department of Zoology and Native Fish Research Group, University of British Columbia, 6270 University Blvd, Vancouver, BC, Canada, V6T 1Z4.
Mol Ecol. 2003 Oct;12(10):2609-22. doi: 10.1046/j.1365-294x.2003.01937.x.
Westslope cutthroat trout (Oncorhynchus clarki lewisi, Salmonidae) are native to the upper Columbia, Missouri, and South Saskatchewan river drainages of western North America and are at the northern periphery of their range in southeastern British Columbia, Canada. We examined geographical variation in allele frequencies at eight microsatellite loci in 36 samples of westslope cutthroat trout from British Columbia to assess levels of population subdivision and to test the hypothesis that different habitat types (principally mainstem vs. above migration barrier habitats) would influence levels of genetic diversity, genetic divergence among populations, and attainment of equilibrium between gene flow and genetic drift. Across all samples, the mean number of alleles per locus was 3.9 and mean expected heterozygosity was 0.56. Population subdivision was extensive with an overall Fst (theta) of 0.32. Populations sampled above migration barriers had significantly fewer alleles, lower expected heterozygosity, but greater average pairwise Fst than populations sampled from mainstem localities. We found evidence for isolation-by-distance from a significant correlation between genetic distance and geographical distance (r = 0.31), but the pattern was much stronger (r = 0.51) when above barrier populations and a population that may have been involved in headwater exchanges were removed. By contrast, isolation-by-distance was not observed when only above barrier populations were tested among themselves. Our data support the maintenance of separate demographic management strategies for westslope cutthroat trout inhabiting different river systems and illustrate how differing habitat structure (e.g. presence of migration barriers) may influence patterns of biodiversity and gene flow-drift equilibrium.
西部斜坡割喉鳟（Oncorhynchus clarki lewisi，鲑科）原产于北美洲西部的哥伦比亚河上游、密苏里河和萨斯喀彻温河上游流域，在加拿大不列颠哥伦比亚省东南部处于其分布范围的北部边缘。我们检测了来自不列颠哥伦比亚省的36个西部斜坡割喉鳟样本在8个微卫星位点上的等位基因频率的地理变异，以评估种群细分水平，并检验不同栖息地类型（主要是干流与迁徙障碍以上的栖息地）是否会影响遗传多样性水平、种群间的遗传分化以及基因流与遗传漂变之间平衡的达成情况。在所有样本中，每个位点的平均等位基因数为3.9，平均期望杂合度为0.56。种群细分程度较高，总体Fst（θ）为0.32。在迁徙障碍以上采集的种群的等位基因明显较少，期望杂合度较低，但平均成对Fst值高于从干流地区采集的种群。我们发现了距离隔离的证据，遗传距离与地理距离之间存在显著相关性（r = 0.31），但当去除障碍以上的种群和一个可能参与源头交流的种群后，这种模式更强（r = 0.51）。相比之下，仅对障碍以上的种群进行相互测试时，未观察到距离隔离现象。我们的数据支持对栖息于不同河流系统的西部斜坡割喉鳟维持单独的种群管理策略，并说明了不同的栖息地结构（如迁徙障碍的存在）可能如何影响生物多样性模式以及基因流 - 遗传漂变平衡。
