Final Report Summary - CICHLIDX (An integrative approach towards the understanding of an adaptive radiation of East African cichlid fishes)
More than 160 years after Darwin and Wallace jointly introduced their theory of evolution by natural selection, the identification of the processes that govern the emergence of novel species remains a fundamental problem to biology. Why is species richness so unequally distributed across the tree of life? Why did some organismal lineages diversify into new forms in a seemingly explosive manner, whereas others have lingered phenotypically unvaried over millions of years? And what is the molecular basis of adaptation and diversification? A key to these and related questions is the comparative study of exceptionally diverse yet relatively recent species assemblages. Owing to their taxonomic, phenotypic, ecological and behavioral diversity and propensity for explosive diversification, the assemblages of cichlid fish in the East African Great Lakes Victoria, Malawi and Tanganyika are important role models in evolutionary biology and highly suited to address these questions. In this project, we scrutinized the cichlid fish assemblage of Lake Tanganyika, which represents the morphologically, ecologically and behaviorally most diverse cichlid adaptive radiation. More specifically, we have sequenced the genomes of two representatives of each of the roughly 250 Tanganyikan cichlid species; we have compiled gene expression profiles in more than 2500 tissue samples; we have quantified the morphology of these species on the basis of 2D and 3D x-ray scans; and have assessed their ecology on the basis of underwater census data and carbon and nitrogen stable isotope measurements. In combination, these data reveal a strong connection between adaptive phenotypes such as body shape and mouth morphology and the environment in which a species lives and forages. Furthermore, the reconstruction of morphological evolution taking into consideration the phylogenetic relationships of the species and the environmental history of the lake highlights the progression of the adaptive radiation in discrete stages. Finally, we are able to link features in the genomes of the Tanganyikan cichlids to elevated rates of diversification. Taken together, our findings help redefine our understanding of adaptive radiation and explosive organismal diversification.