In vertebrates, the East African cichlid radiations represent arguably the most dramatic examples of adaptive speciation. In the great lakes Victoria, Malawi and Tanganyika and within the last few million years, one or a few ancestral lineages of haplochromine cichlid fish have given rise to over 1500 species exhibiting an unprecedented diversity of morphological and ecological adaptations. Such explosive phenotypic diversification of East African cichlids is unparalleled among vertebrates and implies the rapid evolution of regulatory regions and networks underlying the traits under selection.
Comparative functional genomics, transcriptomics and epigenomics are powerful tools to study the evolution of tissue and species divergence. We recently developed Arboretum, an algorithm to identify modules of co-expressed genes across multiple species in a phylogeny. By integrating inferred modules with nucleotide variation, predicted cis regulatory elements and miRNA profiles from five East African Cichlids, we investigated the evolution of tissue-specific gene regulation. Our analyses identified modules with tissue-specific patterns for which we reconstructed the evolutionary gene regulatory networks across the five cichlids species. We report striking cases of rapid network rewiring for genes known to be involved in traits under natural and/or sexual selection such as jaw morphology (dlx2a), visual systems (rho) and pigmentation (ednrb1a). Our unique integrative approach that interrogates the evolution of regulatory networks allowed us to identify the rapid regulatory changes associated with certain traits under selection in cichlids.