Understanding genetic structure and gene flow can elucidate the mechanisms of diversification and adaptation in seabirds and help define conservation and management units. From 2012 to 2016, we collected blood and feather samples from 156 Red‐billed Tropicbirds (Phaethon aethereus) from seven colonies distributed along the Gulf of California and Mexican tropical Pacific to estimate genetic diversity, genetic structure, and gene flow using microsatellite markers and mitochondrial DNA (mtDNA; control region) sequences. Nuclear and mtDNA data revealed relatively low or null levels of genetic diversity, respectively, possibly the result of a founder effect in the eastern Pacific followed by a subsequent population expansion. Nuclear data revealed significant genetic structure among the colonies, but the differences were not associated with regional grouping (i.e., Gulf of California vs. Tropical Pacific). Greater gene flow was observed from the tropical Pacific toward the Gulf of California, possibly related to shared dispersal patterns during the non‐breeding season (individuals traveling north to reach warm currents with abundant prey). With the exception of one colony in the Mexican tropical Pacific, we found no evidence of recent bottleneck events. Nonetheless, the overall reduced genetic diversity suggests a high intrinsic vulnerability and risk of extinction for this species.

中文翻译：

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墨西哥太平洋红嘴热带鸟的遗传结构和多样性低

了解遗传结构和基因流动可以阐明海鸟的多样化和适应机制，并有助于确定保护和管理单位。从2012年到2016年，我们从156只红嘴热带鸟（Phaethon aethereus）采集了血液和羽毛样本）分布在沿着加利福尼亚湾和墨西哥热带太平洋分布的七个殖民地，以使用微卫星标记和线粒体DNA（mtDNA;控制区）序列估算遗传多样性，遗传结构和基因流。核和mtDNA数据分别显示出相对较低或无效的遗传多样性水平，这可能是东太平洋建立者效应和随后的人口扩张的结果。核数据显示出这些殖民地之间具有重要的遗传结构，但差异与区域分组无关（即加利福尼亚湾与热带太平洋）。从热带太平洋流向加利福尼亚湾的基因流更大，可能与非繁殖季节共享的散布模式有关（个体向北移动以到达具有丰富猎物的暖流）。除了墨西哥热带太平洋地区的一个殖民地外，我们没有发现近期瓶颈事件的证据。但是，总体而言，遗传多样性的降低表明该物种具有很高的内在脆弱性和灭绝风险。