Data from: Implications of the circumpolar genetic structure of polar bears for their conservation in a rapidly warming Arctic

We provide an expansive analysis of polar bear (Ursus maritimus) circumpolar genetic variation during the last two decades of decline in their sea-ice habitat. We sought to evaluate whether their genetic diversity and structure have changed over this period of habitat decline, how their current genetic patterns compare with past patterns, and how genetic demography changed with ancient fluctuations in climate. Characterizing their circumpolar genetic structure using microsatellite data, we defined four clusters that largely correspond to current ecological and oceanographic factors: Eastern Polar Basin, Western Polar Basin, Canadian Archipelago and Southern Canada. We document evidence for recent (ca. last 1–3 generations) directional gene flow from Southern Canada and the Eastern Polar Basin towards the Canadian Archipelago, an area hypothesized to be a future refugium for polar bears as climate-induced habitat decline continues. Our data provide empirical evidence in support of this hypothesis. The direction of current gene flow differs from earlier patterns of gene flow in the Holocene. From analyses of mitochondrial DNA, the Canadian Archipelago cluster and the Barents Sea subpopulation within the Eastern Polar Basin cluster did not show signals of population expansion, suggesting these areas may have served also as past interglacial refugia. Mismatch analyses of mitochondrial DNA data from polar and the paraphyletic brown bear (U. arctos) uncovered offset signals in timing of population expansion between the two species, that are attributed to differential demographic responses to past climate cycling. Mitogenomic structure of polar bears was shallow and developed recently, in contrast to the multiple clades of brown bears. We found no genetic signatures of recent hybridization between the species in our large, circumpolar sample, suggesting that recently observed hybrids represent localized events. Documenting changes in subpopulation connectivity will allow polar nations to proactively adjust conservation actions to continuing decline in sea-ice habitat.本研究针对海冰栖息地持续缩减的近二十年间，环极地分布的北极熊（Ursus maritimus）的遗传变异展开全面分析。我们旨在厘清在此栖息地缩减周期内，北极熊的遗传多样性与群体遗传结构是否发生改变，对比其当前遗传模式与历史遗传模式的差异，并解析遗传种群动态如何随古气候波动发生演变。本研究借助微卫星（microsatellite）标记数据解析其环极地遗传结构，共界定出四大遗传聚类群，其分布大体契合当前的生态与海洋学特征：东极盆地群、西极盆地群、加拿大北极群岛群与加拿大南部群。研究证实，近期（约过去1至3个世代）存在从加拿大南部群与东极盆地群向加拿大北极群岛群的定向基因流——该区域被推测为气候驱动的海冰栖息地持续缩减背景下，北极熊未来的适宜避难所。本研究数据为该假说提供了实证支撑。当前的基因流方向与全新世时期的既往基因流模式存在显著差异。通过对线粒体DNA（mitochondrial DNA）的分析，加拿大北极群岛聚类群与东极盆地聚类群内的巴伦支海亚种群均未检测到种群扩张信号，这表明这些区域或许也曾作为过往间冰期的避难所。对北极熊与并系棕熊（U. arctos）的线粒体DNA错配分析显示，两个物种的种群扩张时间存在显著偏移，该差异可归因于二者对过往气候周期的种群动态响应存在分化。与存在多个演化支的棕熊不同，北极熊的线粒体基因组结构较为浅显且形成时间较晚。在本研究庞大的环极地采样样本中，未检测到两物种间近期杂交的遗传信号，这表明近期观测到的杂交个体仅为局地偶发现象。厘清亚种群连通性的变化，将有助于北极沿岸国家主动调整保护策略，以应对持续缩减的海冰栖息地。