Microsatellite data reveals weak population substructuring in Copadichromis sp 'virginalis kajose', a demersal cichlid from Lake Malawi, Africa

Small but significant differences were found in allele frequencies among fi ve populations (overall F-ST estimate (theta)=0.004, P=0.006; overall F-ST estimate (RHO)=0.019, P <0.00001) of the demersal cichlid Copadichromis sp. 'virginalis kajose', collected from five locations in Lake Malawi. Pairwis e FST estimates revealed significant differences between the most southerly population (Cape Maclear), and the three most northerly populations (Mbamb a Bay, Metangula and Chilola). Pairwise F-ST estimates also revealed signif icant differences between some populations, but no geographical pattern was discernible. There was no evidence of isolation by distance using either t he shortest straight-line distance between samples, or the distance around the shoreline following a 50 ra depth contour. F-ST estimates were consider ably lower than found in previous studies on the mbuna (rock-dwelling speci es), but higher than those found in a study of three pelagic cichlid specie s from Lake Malawi. Substructuring in C. sp. 'virginalis kajose' appears to be on a similar scale to the Atlantic cod.,C (C) 2001 The Fisheries Societ y of the British Isles.