Abstract
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.
Highlights
Contemporary patterns of genetic diversity and population connectivity within species are influenced by demographic history, historical and present barriers to gene flow, and the species’ active and/or passive dispersal ability (Hewitt, 2000; Ellegren & Galtier, 2016)
Genetic diversity was somewhat higher in the eupelagic species B. fasciatus and B. leo than in the benthopelagic species B. graueri and H. stenosoma (Table 1)
The fits of the observed mismatch distributions to the expectations based on growth parameter estimates, with nonsignificant sum of squared differences (SSD) and rg values, indicated recent population growth in B. fasciatus, B. leo, both clades of B. graueri and the northern cade of H. stenosoma (Fig. 3)
Summary
Contemporary patterns of genetic diversity and population connectivity within species are influenced by demographic history, historical and present barriers to gene flow, and the species’ active and/or passive dispersal ability (Hewitt, 2000; Ellegren & Galtier, 2016). Highly vagile generalist species with great active dispersal ability typically show little phylogeographic structure, sometimes even across their entire distribution range (e.g., Koblmuller et al, 2012; Statham et al, 2014; Nebel et al, 2015; Pfeiler & Markow, 2017) This is true for pelagic fishes, which are usually highly mobile with their dispersal not restricted by physical barriers (e.g., Graves & McDowell, 2003; Theisen et al, 2008; Garcıa-Rodrıguez et al, 2011), even though exceptions have been reported (e.g., Perrin & Borsa, 2001; Lu et al, 2006; Fauvelot & Borsa, 2011; Sebastian et al, 2017).
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