Genetic population structure indicates sympatric speciation of Lake Malawipelagic cichlids

Allopatric processes of speciation have routinely been presented to explain the extraordinary radiation of the East African Great Lakes cichlid fish s pecies flocks. The 21 or more species of pelagic cichlids within the Lake M alawi flock appear to have lake-wide distributions that challenge such a co ncept. Data from six microsalellite DNA loci indicate single, panmictic pop ulations across the lake of three Diplotaxodon species. Levels of variabili ty) at these loci suggest that populations have been large and stable. mito chondrial DNA sequence data (872bp of control region + 981 bp of the NADH-2 ) from 90 species, representing all major clades within the Lake Malawi flo ck, indicate reciprocal monophyly of the pelagic clade. We suggest that the se data support a hypothesis that speciation in sympatry is more plausible land widespread) within the cichlid species flocks than previously thought.