RNAseq of New and Old World thick-lipped cichlid fishes
The ecological and genetic basis of convergent thick-lipped phenotypes in cichlid fishes
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 East African Great Lakes.  Unlike most convergent forms in cichlids, which are restricted to East Africa, the  thick-lipped phenotype also occurs elsewhere, e.g. in the Central American Midas  Cichlid 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 African (Lobochilotes  labiatus) and a Central American (Amphilophus labiatus) thick-lipped species and  observed the feeding behavior in East Africa. We found that the thick-lipped species  evolved at an early stage of the respective radiation, that its evolution was associated  with similar morphological adaptations, and that the ‘fleshy’ lips are associated with  hard-shelled prey in the form of mollusks and invertebrates. We then used  comparative Illumina RNA sequencing of thick versus normal lip tissue in East  African 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: Actb, Cldn7 and Copb. The function of these genes can be  linked to the loose connective tissue constituting the fleshy lips. Similar trends in gene  expression between African and Central American thick-lipped species appear to  indicate that an overlapping set of genes was independently recruited to build this  particular phenotype in both lineages.