Population divergence and gene flow in an endangered and highly mobile seabird

Seabirds are highly vagile and can disperse up to thousands of kilometers, therefore it can be difficult to identify the factors that promote isolation between populations. The endemic Hawaiian petrel (Pterodroma sandwichensis) is one such species. Today it is endangered, and known to breed only on the islands of Hawaii, Maui, Lanai, and Kauai. Historical records indicate that a large population formerly bred on Molokai as well, but this population has recently been extirpated. Given the great dispersal potential of these petrels it remains unclear if populations are genetically distinct and which factors may contribute to isolation between them. We sampled petrels from across their range, including individuals from the extirpated Molokai population. We sequenced 524 bp of mitochondrial DNA, 741 bp from three nuclear introns, and genotyped 18 microsatellite loci in order to examine patterns of divergence in this species and to investigate the potential underlying mechanisms. Mitochondrial and nuclear data sets indicated significant genetic differentiation among all modern populations, but no differentiation was found between historic samples from Molokai and modern birds from Lanai. Population-specific non-breeding distribution or perhaps strong natal philopatry may reduce gene flow between populations. However, the lack of population structure between extirpated Molokai birds and modern birds on Lanai suggests that petrels may be able to overcome these barriers and disperse prior to complete extirpation. Hawaiian petrel populations should be managed as distinct units, except potentially for the dwindling population on Hawaii, which may require translocation to prevent extirpation in the near future.

海鸟具有极高的移动扩散能力，可迁移数千公里之远，因此难以识别推动种群间产生隔离的相关因素。夏威夷圆尾鹱（Pterodroma sandwichensis）便是这类物种之一。目前该物种已处于濒危状态，已知仅在夏威夷岛、毛伊岛、拉奈岛及考爱岛繁殖。历史记录显示，此前莫洛凯岛也曾存在大规模繁殖种群，但该种群现已局部灭绝。鉴于这类圆尾鹱极强的扩散潜力，目前仍不清楚其各个种群是否存在遗传分化，以及哪些因素可能促成种群间的隔离。本研究对该物种分布范围内的圆尾鹱进行了采样，其中包括来自已局部灭绝的莫洛凯岛种群的个体。为解析该物种的遗传分化模式并探究其潜在机制，我们对524个碱基对的线粒体DNA（mitochondrial DNA）、3个核内含子（nuclear introns）共741个碱基对的序列进行了测序，并对18个微卫星位点（microsatellite loci）进行了基因分型。线粒体DNA与核基因数据均显示，所有现存种群间均存在显著的遗传分化，但莫洛凯岛历史样本与拉奈岛现存个体之间未检测到遗传分化。种群特有的非繁殖分布格局，或是强烈的出生恋巢性（natal philopatry），或许会降低种群间的基因流。然而，已局部灭绝的莫洛凯岛个体与拉奈岛现存个体之间缺乏种群遗传结构，这表明圆尾鹱或可在种群彻底灭绝前突破这些障碍并完成扩散。夏威夷圆尾鹱的各个种群应作为独立管理单元进行保护，唯有夏威夷岛日渐萎缩的种群除外——该种群或需实施个体迁地保育，以避免在近期彻底灭绝。