The ecological and genetic basis of convergent thick‐lipped phenotypes in cichlid fishes

Abstract

The evolution of convergent phenotypes is one of the most interesting outcomes of replicate adaptive radiations. Remarkable cases of convergence involve the thick‐lipped phenotype found across cichlid species flocks in the E ast A frican G reat L akes. Unlike most other convergent forms in cichlids, which are restricted to E ast A frica, the thick‐lipped phenotype also occurs elsewhere, for example in the C entral A merican M idas C ichlid assemblage. Here, we use an ecological genomic approach to study the function, the evolution and the genetic basis of this phenotype in two independent cichlid adaptive radiations on two continents. We applied phylogenetic, demographic, geometric morphometric and stomach content analyses to an A frican ( L obochilotes labiatus ) and a C entral A merican ( A mphilophus labiatus ) thick‐lipped species. We found that similar morphological adaptations occur in both thick‐lipped species and that the ‘fleshy’ lips are associated with hard‐shelled prey in the form of molluscs and invertebrates. We then used comparative I llumina RNA sequencing of thick vs. normal lip tissue in E ast A frican cichlids and identified a set of 141 candidate genes that appear to be involved in the morphogenesis of this trait. A more detailed analysis of six of these genes led to three strong candidates: A ctb , C ldn7 and C opb . The function of these genes can be linked to the loose connective tissue constituting the fleshy lips. Similar trends in gene expression between A frican and C entral A merican thick‐lipped species appear to indicate that an overlapping set of genes was independently recruited to build this particular phenotype in both lineages.

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