Molecular basis of a novel pigment trait in cichlid fishes

The genetics underlying the evolution of novel morphological structures is a fascinating topic that has attracted the attention of many evolutionary biologists. Among the East African cichlid fauna, the haplochromines represent the most species-rich group. One of their characteristics is the occurrence of egg-spots on the anal fins of males, which mimic real eggs and play a crucial role in the breeding cycle of these maternal mouthbrooding fish. These yellow to orange egg-spots serve as intra-specific sexual advertisement to attract females and to maximize breeding success. They are a novel trait that emerged only once in the evolution of the haplochromine lineage. The main goal of this doctoral thesis was to deepen our understanding of the genetics and developmental basis of the emergence and diversification of egg-spots, an evolutionary novelty in East African cichlid fishes. Further understanding of the molecular basis novelty requires the identification of the genes and mutations that underlie these major phenotypic changes. Here we report the identification of two genes that are involved in the development of the egg-spot trait Ð fhl2a and fhl2b Ð and one possible cis-regulatory mutation in fhl2b that might have played a role in the emergence of the egg-spot trait. We further described many more candidate genes via an RNAseq survey of Astatotilapia burtoni (haplochromine species) egg-spot and anal fin transcriptome. We generated hypotheses about their possible function using Gene Ontology definitions and inter-species gene expression, establishing a database that will serve as an important resource and useful resource for future research on the emergence and diversification the egg-spot trait.