Continental diversification of an African catfish radiation (Mochokidae: Synodontis).

Despite African rivers containing high species diversity, continental-scale studies investigating the mechanisms generating biological diversity of African riverine faunas are limited compared with lacustrine systems. To investigate the build-up of diversity in a tropical aquatic continental radiation, we test different models of lineage diversification and reconstruct the biogeographic history in a species-rich siluriform genus, Synodontis (~130 species), with a broad distribution across all major tropical African drainage basins. The resulting robust species-level phylogeny (~60% complete, based on a multigene data set) exhibits a near constant rate of lineage accumulation throughout the mid-Cenozoic to recent, irrespective of missing species and despite the changing environmental conditions that were prevalent during this time period. This pattern contrasts with the findings for species-level diversification of large clades that commonly show an early burst of cladogenesis followed by declining rates through time. The identification of distinct biogeographic clades demonstrates a correlation between river hydrology and cladogenesis, although there is evidence of recent repeat dispersal into the southern range of the focal group. We conclude that diverse freshwater fish radiations with tropical continental distributions represent important organisms to test hypotheses of diversification and investigate the effects of palaeo-landscapes and climates on present day biodiversity.

Mastacembelid eels support Lake Tanganyika as an evolutionary hotspot of diversification.

BACKGROUND: Lake Tanganyika (LT) is the oldest of the African Rift Lakes and is one of the richest freshwater ecosystems on Earth, with high levels of faunal diversity and endemism. The endemic species flocks that occur in this lake, such as cichlid fishes, gastropods, catfish and crabs, provide unique comparative systems for the study of patterns and processes of speciation. Mastacembelid eels (Teleostei: Mastacembelidae) are a predominately riverine family of freshwater fish, occurring across Africa and Asia, but which also form a small species flock in LT. METHODS: Including 25 species across Africa, plus Asian representatives as outgroups, we present the first molecular phylogenetic analysis for the group, focusing particularly on the evolutionary history and biodiversity of LT mastacembelid eels. A combined matrix of nuclear and mitochondrial genes based on 3118 bp are analysed implementing different phylogenetic methods, including Bayesian inference and maximum likelihood. RESULTS: LT Mastacembelus are recovered as monophyletic, and analyses reveal the rapid diversification of five main LT lineages. Relaxed molecular clock dates provide age estimates for the LT flock at approximately 7-8 Myr, indicating intralacustrine diversification, with further speciation events coinciding with periods of lower lake level. Our analyses also reveal as yet undescribed diversity of lacustrine and riverine species. A Southern-Eastern African clade, that is younger than the LT flock, is also recovered, while West African taxa are basal members of the African mastacembelid clade. CONCLUSIONS: That the LT species flock of mastacembelid eels appears to have colonised and immediately diversified soon after the formation of the lake, supports the view of LT as an evolutionary hotspot of diversification. We find evidence for biogeographic clades mirroring a similar pattern to other ichthyological faunas. In addition, our analyses also highlight a split of African and Asian mastacembelid eels at approximately 19 Myr that is considerably younger than the split between their associated continents, suggesting a dispersal scenario for their current distribution.