Data from: Population structure and historical demography of South American sea lions provide insights into the catastrophic decline of a marine mammal population

Understanding the causes of population decline is crucial for conservation management. We therefore used genetic analysis both to provide baseline data on population structure and to evaluate hypotheses for the catastrophic decline of the South American sea lion (Otaria flavescens) at the Falkland Islands (Malvinas) in the South Atlantic. We genotyped 259 animals from 23 colonies across the Falklands at 281 bp of the mitochondrial hypervariable region and 22 microsatellites. A weak signature of population structure was detected, genetic diversity was moderately high in comparison with other pinniped species, and no evidence was found for the decline being associated with a strong demographic bottleneck. By combining our mitochondrial data with published sequences from Argentina, Brazil, Chile and Peru, we also uncovered strong maternally directed population structure across the geographical range of the species. In particular, very few shared haplotypes were found between the Falklands and South America, and this was reflected in correspondingly low migration rate estimates. These findings do not support the prominent hypothesis that the decline was caused by migration to Argentina, where large-scale commercial harvesting operations claimed over half a million animals. Thus, our study not only provides baseline data for conservation management but also reveals the potential for genetic studies to shed light upon long-standing questions pertaining to the history and fate of natural populations.

阐明种群衰退的成因，对于物种保护管理工作至关重要。为此，我们采用遗传分析方法，既获取了种群结构的基线数据，也对南大西洋福克兰群岛（马尔维纳斯）区域南美海狮（Otaria flavescens）发生灾难性种群衰退的相关假说开展了验证。我们对福克兰群岛境内23个聚居群的259头个体进行了基因分型，检测位点涵盖线粒体高变区（mitochondrial hypervariable region）的281 bp片段与22个微卫星标记（microsatellites）。研究结果显示种群结构仅存在微弱的分化信号；相较于其他鳍足类动物（pinniped species），该区域南美海狮的遗传多样性处于中等偏高水平；未发现种群衰退与强烈的种群瓶颈（demographic bottleneck）存在关联的证据。我们将自身获得的线粒体数据与阿根廷、巴西、智利及秘鲁已发表的序列进行整合分析后，还发现该物种在整个分布区域内存在显著的母系遗传种群结构。具体而言，福克兰群岛与南美区域之间几乎不存在共享单倍型（haplotypes），这一特征也对应着较低的种群迁移率估计值。上述发现并不支持当前主流假说：即种群衰退系海狮迁移至阿根廷海域所致——当地大规模商业捕捞活动已致使超过50万头海狮被捕杀。综上，本研究不仅为物种保护管理提供了基线数据，同时也揭示了遗传分析手段可用于解析长期困扰学界的自然种群历史与命运相关问题的潜力。