In the absence of dispersal barriers, species with great dispersal ability are expected to show little, if at all, phylogeographic structure. The East African Great Lakes and their diverse fish faunas provide opportunities to test this hypothesis in pelagic fishes, which are presumed to be highly mobile and unrestricted in their movement by physical barriers. Here, we address the link between panmixis and pelagic habitat use by comparing the phylogeographic structure among four deepwater cichlid species of the tribe Bathybatini from Lake Tanganyika. We show that the mitochondrial genealogies (based on the most variable part or the control region) of the four species are very shallow (0.8–4% intraspecific divergence across entire distribution ranges) and that all species experienced recent population growth. A lack of phylogeographic structure in the two eupelagic species, Bathybates fasciatus and B. leo, was consistent with expectations and with findings in other pelagic cichlid species. Contrary to expectations, a clear phylogeographic structure was detected in the two benthopelagic species, B. graueri and Hemibates stenosoma. Differences in genetic diversity between eupelagic and benthopelagic species may be due to differences in their dispersal propensity, mediated by their respective predatory niches, rather than precipitated by external barriers to dispersal.

中文翻译：

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只有真正的中上层生物混合：坦噶尼喀湖深水慈鲷的比较系统发育地理学

在没有扩散障碍的情况下，具有强大扩散能力的物种预计不会显示出系统发育地理学结构（如果有的话）。东非五大湖及其多样化的鱼类区系为在中上层鱼类中检验这一假设提供了机会，这些鱼类被认为具有高度流动性，并且其运动不受物理障碍的限制。在这里，我们通过比较坦噶尼喀湖Bathybatini部落的四种深水丽鱼物种的系统发育地理结构来探讨panmixis和远洋栖息地利用之间的联系。我们表明，这四个物种的线粒体谱系（基于变化最大的部分或控制区域）非常浅（整个分布范围内的种内差异为 0.8-4%），并且所有物种都经历了最近的种群增长。两种上层物种Bathybates fasciatus和B.leo缺乏系统发育地理结构，这与预期和其他中上层慈鲷物种的发现一致。与预期相反，在两种底栖物种（B. graueri 和 Hemibates stenosoma）中检测到了清晰的系统发育地理结构。上层和海底物种之间遗传多样性的差异可能是由于它们的扩散倾向的差异，这是由它们各自的捕食生态位介导的，而不是由外部扩散障碍促成的。