The best way to observe a fish is to
become a fish sequence its genome.
– Adapted from Jacques Yves Costeau
The speciation of Coptodon cichlids might have been driven by smell.
African cichlids are a textbook example of rapid speciation. In the lakes of East Africa, thousands of species have originated in the geological blink of an eye (check these excellent reviews by Thomas Kocher and Ole Seehausen for more detailed information). A recent study in Molecular Ecology investigated one of the many cichlid radiations and uncovered a peculiar pattern of gene flow.
Three isolated lakes in Cameroon house four cichlid radiations. Two of these lakes are crater lakes, while the third one (Lake Ejagham) is probably the result of a meteor impact. The latter lake houses four species of Coptodon cichlids. Previous work found evidence for gene flow from river populations into this lake. Jelmer Poelstra and his colleagues explored the evolutionary history of these cichlids in more detail.
The researchers sequenced the genomes of three species in the lake (C. fusiforme, C. deckerti and C. ejagham) and two riverine species (C. guineensis and the undescribed C. sp. “Mamfé”). The comparison of these genomes confirmed the results from the previous study: there has been gene flow from riverine species into Lake Ejagham.
Further analyses revealed that a particular genomic region was transferred from C. sp. “Mamfé” into C. deckerti and C. ejagham. This transfer happened just before the divergence of the latter two species. Could this genomic region have initiated a speciation event?
Interestingly, this genomic regions contained a cluster of eight olfactory receptor genes. Olfactory receptors – “smell genes” if you will – have often been linked to the origin of new species. Several fish species use smell to recognize members from their species. Whether smell has also been important in the Coptodon radiation remains to be investigated, but it seems like a plausible scenario.
Poelstra, J.W., Richards, E.J. & Martin, C.H. (2018) Speciation in sympatry with ongoing secondary gene flow and a potential olfactory trigger in a radiation of Cameroon cichlids. Molecular Ecology.