In search of the missing genomic link between two massive adaptive radiations in cichlid fishes:

Adaptive radiation, the phenomenon of rapid diversification of an ancestral lineage into a multitude of new species through ecological diversification, has fascinated evolutionary biologist for a long time. This is not least because adaptive radiation is considered to be responsible for much of the biodiversity on earth. Over the past decades, hybridization between diverging lineages as well as gene flow into the ancestral lineages of adaptive radiation have increasingly been recognized as triggers of this process. This is also true for the species assemblages of cichlid fishes in the African Great Lakes Victoria, Malawi and Tanganyika, which – because of their spectacular diversity – belong to the most celebrated examples of adaptive radiation. However, most available studies in African cichlid fishes have focused on the lacustrine adaptive radiations while paying only marginal attention to the riverine cichlid fauna of the surrounding drainage system. This is particularly true for recent genome-wide studies, in which literally hundreds of low-coverage genomes of lacustrine taxa but only few riverine taxa (e.g. Astatotilapia like cichlids) have sequenced. Consequently, many lineages which might have contributed to the genomic substrate of the massive adaptive radiations in lakes such as Lake Tanganyika and Lake Malawi have not been sampled at the level of genomes. A comprehensive examination of the riverine cichlid fauna of East Africa would, however, be crucial to fully understand the evolutionary mechanism and genomic features underlying the lacustrine adaptive radiations. This project aims at closing this “genome sampling gap" by focusing on the underexplored riverine cichlid diversity of the biogeographically important region situated between Lake Tanganyika and Lake Malawi. More precisely, I plan to sequence 96 draft-genomes of different haplochromine lineages expected to be present in this region, including representatives the ‘Pseudocrenilabrus-group’, the ‘serranochromines’ and Astatotilapia. This genomic data, in combination with an in-depth taxonomic evaluation of the taxa, will allow me to assess whether or not additional – yet undiscovered – ancient gene flow from riverine lineages into the ancestral lineages of the adaptive radiations of Lake Tanganyika and Lake Malawi have occurred, and, if so, to explore the genomic contribution of introgression-derived variants in these exceptionally species-rich vertebrate radiations.