Biogeography and population genetics of the Lake Malawi cichlid Melanochromis auratus: habitat transience, philopatry and speciation

Migration rates among nine populations of the endemic Lake Malawi cichlid M elanochromis auratus were estimated along a 42-km stretch of habitat in the southern end of the lake. Allele frequencies were surveyed at four simple sequence repeat (SSR) loci. The data suggest migration rates among populati ons are quite low. Exact tests indicate that statistically detectable allel e frequency differences exist between many adjacent populations in the stud y. The Fs, value among all populations was estimated to be 0.151 (P < 0.000 2). A biogeographic survey suggests that the highest levels of genetic diff erentiation exist between populations separated by stretches of deep water. Migration is more common between populations separated by shallower water or with shoreline dispersal routes. Reduced allelic diversity was observed at more recently created habitat patches, suggesting that either bottleneck s are associated with the colonization of new habitat patches or that these shallower sites were all founded by genetically depauperate ancestral popu lations. The extreme philopatry of M. auratus, coupled with the patchy dist ribution and transient nature of its preferred habitat, provides opportunit ies for both selection and genetic drift to produce genetic differentiation among populations. Both processes may be important to the evolution of tax onomic diversity in the East African cichlid species flocks.