Speciation within genomic networks: a case study based on Steatocranus cichlids of the lower Congo rapids

Hybridization in animals is a much more common phenomenon as previously thought and may have profound implications for speciation research. The cichlid genus Steatocranus (Teleostei: Cichlidae), a close relative to members of the East African cichlid radiations, radiated under riverine conditions in the lower Congo rapids and produced a small species flock. Previous phylogenetic analyses suggested that hybridization occurred and contributed to speciation in this genus. A re-analysis of an already published 2000 loci-AFLP data set explicitly testing for patterns of ancient gene flow provided strong evidence for a highly reticulate phylogenetic history of the genus. We provide, to our knowledge, the first example of a complex reticulate network in vertebrates, including multiple closely related species connected through ancient as well as recent gene flow. In this context, the limited validity of strictly bifurcating tree hypotheses as a phylogenetic basis for hypothesis testing in evolutionary biology is discussed.