Genetic variation in sea otters (Enhydra lutris) from the North Pacific with relevance to the threatened Southwest Alaska distinct population segment

For the sea otter (Enhydra lutris), genetic population structure is an area of research that has not received significant attention, especially in Southwest Alaska where that distinct population segment has been listed as threatened since 2005 pursuant to the U.S. Endangered Species Act. In this study, 501 samples from 14 locations from Prince William Sound, Alaska to the Commander Islands in Russia were analyzed for variation at 13 microsatellite loci. Our results indicate a high degree of genetic divergence among the 14 locations (FST = 0.12) with gene flow conforming to the isolation by distance (IBD) model (r2 = 0.491, p < 0.05). The 14 sampling locations formed six geographic associations in clustering and ordination analyses that likely correspond to remnant population lineages: 1) Southcentral Alaska, 2) Kodiak and North Alaska Peninsula, 3) South Alaska Peninsula and Bristol Bay, 4) Eastern Aleutian, 5) Western Aleutian, and 6) the Commander Islands. Except for South Alaska Peninsula and Bristol Bay, these clusters closely agree with previously defined stock and management unit boundaries. Our results reveal significant genetic population structure and are generally congruent with current management strategies for the threatened Southwest Alaska distinct population segment.

海獭（Enhydra lutris）的种群遗传结构是长期未得到充分关注的研究领域，尤其是阿拉斯加州西南部区域——该区域的海獭显著种群单元（distinct population segment）自2005年起已依据《美国濒危物种法案》被列为受威胁物种。本研究对采集自美国阿拉斯加州威廉王子湾至俄罗斯科曼多尔群岛的14个采样位点的501份样本展开分析，检测了13个微卫星位点（microsatellite loci）的遗传变异情况。研究结果表明，14个采样位点间存在高度显著的遗传分化（FST=0.12），且基因流符合距离隔离（isolation by distance, IBD）模型（r²=0.491，p<0.05）。聚类与排序分析显示，14个采样位点可划分为6个地理类群，这些类群大概率对应残存的种群谱系：1）阿拉斯加中南部；2）科迪亚克岛与阿拉斯加半岛北部；3）阿拉斯加半岛南部与布里斯托尔湾；4）阿留申群岛东部；5）阿留申群岛西部；6）科曼多尔群岛。除阿拉斯加半岛南部与布里斯托尔湾类群外，其余聚类结果与此前划定的种群管理单元及管理边界高度吻合。本研究揭示了海獭种群存在显著的遗传结构，整体上与当前针对阿拉斯加州西南部受威胁显著种群单元的管理策略相符。