On the origin of Lake Malawi cichlid species: A population genetic analysis of divergence

The cichlid fishes of Lake Malawi are famously diverse. However, phylogenetic and population genetic studies of their history have been difficult because of the great amount of genetic variation that is shared between species. We apply a recently developed method for fitting the "isolation with migration" divergence model to a data set of specially designed compound loci to develop portraits of cichlid species divergence. Outgroup sequences from a cichlid from Lake Tanganyika permit model parameter estimates in units of years and effective population sizes. Estimated speciation times range from 1,000 to 17,000 years for species in the genus Tro-pheops. These exceptionally recent dates suggest that Malawi cichlids as a group experience a very active and dynamic diversif ication process. Current effective population size estimates range form 2,000 to near 40,000, and to > 120,000 for estimates of ancestral population sizes. It appears that very recent speciation and gene flow are among the reasons why it has been difficult to discern the phylogenetic history of Malawi cichlids.