1School of Biological Sciences, University of East Anglia, Norwich, U.K. NR4 7TJ

Population structure in the demersal cichlids of Lake Malawi

Lake Malawi boasts a spectacular cichlid fish fauna, probably exceeding 1000 species. These species have evolved at an unparalleled rate. Evidence from geological and molecular studies suggest that the entire haplochromine cichlid flock may have evolved from a single ancestor in less than 1 million years. Recent studies demonstrate that habitat discontinuities such as areas of deep water or stretches of sand can prevent gene flow between adjacent communities of rock dwelling mbuna. While the mbuna appear to have evolved in an allopathic manner with the presence of physical barriers to reproduction, there are many hundreds of sand-dwelling demersal cichlid species that live in an area apparently devoid of such barriers. Microsatellite markers were used to investigate whether demersal species are divided into reproductively isolated sub-populations. Levels of gene flow were calculated and the approximate geographic distance required to prevent or substantially reduce gene flow estimates.