Malenfant René M, Davis Corey S, Cullingham Catherine I, Coltman David W
Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada.
PLoS One. 2016 Mar 14;11(3):e0148967. doi: 10.1371/journal.pone.0148967. eCollection 2016.
Recently, an extensive study of 2,748 polar bears (Ursus maritimus) from across their circumpolar range was published in PLOS ONE, which used microsatellites and mitochondrial haplotypes to apparently show altered population structure and a dramatic change in directional gene flow towards the Canadian Archipelago-an area believed to be a future refugium for polar bears as their southernmost habitats decline under climate change. Although this study represents a major international collaborative effort and promised to be a baseline for future genetics work, methodological shortcomings and errors of interpretation undermine some of the study's main conclusions. Here, we present a reanalysis of this data in which we address some of these issues, including: (1) highly unbalanced sample sizes and large amounts of systematically missing data; (2) incorrect calculation of FST and of significance levels; (3) misleading estimates of recent gene flow resulting from non-convergence of the program BayesAss. In contrast to the original findings, in our reanalysis we find six genetic clusters of polar bears worldwide: the Hudson Bay Complex, the Western and Eastern Canadian Arctic Archipelago, the Western and Eastern Polar Basin, and-importantly-we reconfirm the presence of a unique and possibly endangered cluster of bears in Norwegian Bay near Canada's expected last sea-ice refugium. Although polar bears' abundance, distribution, and population structure will certainly be negatively affected by ongoing-and increasingly rapid-loss of Arctic sea ice, these genetic data provide no evidence of strong directional gene flow in response to recent climate change.
最近，一项对来自环极分布范围内的2748只北极熊（Ursus maritimus）的广泛研究发表在《公共科学图书馆·综合》上，该研究使用微卫星和线粒体单倍型，显然显示出种群结构的改变以及基因流向加拿大群岛的方向发生了巨大变化——随着气候变化导致其最南端栖息地减少，该地区被认为是北极熊未来的避难所。尽管这项研究代表了一项重大的国际合作努力，并有望成为未来遗传学工作的基线，但方法上的缺陷和解释错误削弱了该研究的一些主要结论。在此，我们对这些数据进行了重新分析，以解决其中的一些问题，包括：（1）样本量高度不平衡以及大量系统性缺失的数据；（2）FST和显著性水平的计算错误；（3）由于程序BayesAss未收敛导致的近期基因流的误导性估计。与最初的研究结果相反，在我们的重新分析中，我们发现全球北极熊有六个遗传集群：哈德逊湾复合体、加拿大北极群岛西部和东部、极地盆地西部和东部，重要的是——我们再次证实，在靠近加拿大预期的最后海冰避难所的挪威湾存在一个独特且可能濒危的北极熊集群。尽管北极海冰持续且日益迅速的流失肯定会对北极熊的数量、分布和种群结构产生负面影响，但这些遗传数据并未提供证据表明近期气候变化导致了强烈的定向基因流。
