Abstract
Geographic isolation is suggested to be among the most important processes in the generation of cichlid fish diversity in East Africa's Great Lakes, both through isolation by distance and fluctuating connectivity caused by changing lake levels. However, even broad scale phylogeographic patterns are currently unknown in many non‐cichlid littoral taxa from these systems. To begin to address this, we generated restriction‐site‐associated DNA sequence (RADseq) data to investigate phylogeographic structure throughout Lake Tanganyika (LT) in two broadly sympatric rocky shore catfish species from independent evolutionary radiations with differing behaviors: the mouthbrooding claroteine, Lophiobagrus cyclurus, and the brood‐parasite mochokid, Synodontis multipunctatus. Our results indicated contrasting patterns between these species, with strong lake‐wide phylogeographic signal in L. cyclurus including a deep divergence between the northern and southern lake basins. Further structuring of these populations was observed across a heterogeneous habitat over much smaller distances. Strong population growth was observed in L. cyclurus sampled from shallow shorelines, suggesting population growth associated with the colonization of new habitats following lake‐level rises. Conversely, S. multipunctatus, which occupies a broader depth range, showed little phylogeographic structure and lower rates of population growth. Our findings suggest that isolation by distance and/or habitat barriers may play a role in the divergence of non‐cichlid fishes in LT, but this effect varies by species.
Highlights
The study of species diversification in biodiverse environments can reveal the importance of different factors influencing species diversity and coexistence
Our findings suggest that isolation by distance and/or habitat barriers may play a role in the divergence of non-cichlid fishes in Lake Tanganyika (LT), but this effect varies by species
For the East African Great Lakes the vast majority of studies have focused on the hyperdiverse cichlid fishes, which may not exemplify the patterns of evolution seen in other fish groups, and it is not known whether the same factors influence other taxa that have diversified in these water bodies
Summary
The study of species diversification in biodiverse environments can reveal the importance of different factors influencing species diversity and coexistence. During the Late Pleistocene glaciations (≈106 Ka), lake levels dropped by ≈435 m, and while the size of LT was considerably reduced, it remained a large and mostly connected water body (McGlue et al, 2008) These lake-level fluctuations have been shown to influence distributions and diversification in multiple cichlid species (e.g., Rüber, Verheyen, & Meyer, 1999; Sefc, Mattersdorfer, Hermann, & Koblmüller, 2017; Sturmbauer, Börger, van Steenberge, & Koblmüller, 2017; Verheyen, Rüber, Snoeks, & Meyer, 1996) primarily through altered habitat barriers and repeated periods of isolation followed by secondary contact (e.g., Egger, Koblmüller, Sturmbauer, & Sefc, 2007; Nevado, Mautner, Sturmbauer, & Verheyen, 2013). Lake-level rises correlate with population expansions allowing the colonization of new habitats (Koblmüller et al, 2011; Winkelmann, Rüber, & Genner, 2017) This complex history has influenced a range of geographic patterns in LT cichlids, as the environment interacts with species-specific ecological characteristics, and population structure varies between even closely related species (e.g., Baric et al, 2003). Species-specific characteristics play a large role, with some species showing little structure (e.g., Koblmüller, Odhiambo, Sinyinza, Sturmbauer, & Sefc, 2015), while in another species, a habitat break as small as 7 km acted as a barrier to dispersal (Sefc et al, 2007)
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