Lacustrine radiations in African Synodontis catfish

Synodontis catfish are a species-rich, tropical pan-African genus that predominately occur in fluviatile environments, but which also form a small radiation within Lake Tanganyika (LT). Here we estimate Synodontis relationships, based on mitochondrial and nuclear DNA, greatly expanding previous sampling. Data were analysed using different methods of phylogenetic inference: Bayesian (also testing compositional heterogeneity), likelihood and parsimony, in order to investigate biogeographic history and the extent of intralacustrine speciation within this group. Bayesian-relaxed clock analyses were used to estimate timings of radiations. Our analyses reveal a single origin of the LT flock with the inclusion of the nonendemic S. victoriae, and that these taxa evolved relatively recently (5.5 Ma), considerably later than the formation of LT (9-12 Ma). Two internal endemic clades diversified at a similar time (2-2.5 Ma), corresponding to a period of climate change, when lake levels dropped. We find evidence for a further species flock, composed of riverine southern African taxa, the diversification of which is very rapid, 0.8 Ma (95% HPD: 0.4-1.5) and infer a similar scenario for the diversification of this flock to southern African serrachromine cichlids in that they radiated in the now extinct lake Makgadikgadi. We also reveal that the biogeographic history of Synodontis catfish is more complex than previously thought, with nonmonophyletic geographic species groupings.