Abstract
BackgroundSqueaker catfishes (Pisces, Mochokidae, Synodontis) are widely distributed throughout Africa and inhabit a biogeographic range similar to that of the exceptionally diverse cichlid fishes, including the three East African Great Lakes and their surrounding rivers. Since squeaker catfishes also prefer the same types of habitats as many of the cichlid species, we hypothesized that the East African Synodontis species provide an excellent model group for comparative evolutionary and phylogeographic analyses.ResultsOur analyses reveal the existence of six major lineages of Synodontis in East Africa that diversified about 20 MYA from a Central and/or West African ancestor. The six lineages show a clear geographic patterning. Two lineages are endemic to Lake Tanganyika (plus one non-endemic representative), and these are the only two Synodontis lineages that diversified further into a small array of species. One of these species is the cuckoo catfish (S. multipunctatus), a unique brood parasite of mouthbrooding haplochromine cichlids, which seems to have evolved in parallel with the radiation of its cichlid host lineage, the Tropheini. We also detect an accelerated rate of molecular evolution in S. multipunctatus, which might be the consequence of co-evolutionary dynamics.ConclusionWe conclude that the ancestral lineage of today's East African squeaker catfish fauna has colonized the area before the Great Lakes have formed. This ancestor diversified rapidly into at least six lineages that inhabit lakes and rivers in East Africa. Lake Tanganyika is the only lake harboring a small species flock of squeaker catfishes.
Highlights
Squeaker catfishes (Pisces, Mochokidae, Synodontis) are widely distributed throughout Africa and inhabit a biogeographic range similar to that of the exceptionally diverse cichlid fishes, including the three East African Great Lakes and their surrounding rivers
In order to obtain a better understanding of the evolution, diversity and phylogeography of East African squeaker catfish, we aimed to reconstruct the phylogeny of East African Synodontis with special emphasis on the sequence and timing of colonization events of the East African Great Lakes Tanganyika, Malawi and Victoria, and the evolution of "cuckooing" behavior in Lake Tanganyika
While our analyses revealed highly consistent results for the most recent common ancestor (MRCA) of the first Tanganyikan clade and that of S. multipunctatus (Table 3), the estimates for the MRCA of S. njassae (Lake Malawi) and that of the second Tanganyikan clade are slightly older than expected based on the presumed formation of the truly lacustrine habitat in both lakes [46,47,48,49]
Summary
Squeaker catfishes (Pisces, Mochokidae, Synodontis) are widely distributed throughout Africa and inhabit a biogeographic range similar to that of the exceptionally diverse cichlid fishes, including the three East African Great Lakes and their surrounding rivers. An initially West African to Central African origin has been proposed for the East African representatives of many of these families [18] Such a scenario has only been confirmed with phylogenetic analyses for the Cichlidae [9,12,19,20,21,22], and Clupeidae (Wilson & Meyer, unpublished), while the Clariidae seem to have colonized Africa from the Arabian plate [23]. Eleven non-cichlid families with about 50 species have been described for Lake Malawi One of these families is not represented in lakes Tanganyika and Victoria: A single anguillid species, the African mottled eel (Anguilla bengalensis labiata), migrates to the area of Lake Malawi via the Zambezi and Shire River. Aside of the Cichlidae, nine other families are known to live in all three Great Lakes: Bagridae, Characidae, Clariidae, Cyprinidae, Cyprinodontidae, Mastacembalidae, Mochokidae, Mormyridae, and Protopteridae
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