Direct mate choice maintains diversity among sympatric cichlids in Lake Victoria

Mate choice may play an important role in animal speciation. The haplochrom ine cichlids of Lake Victoria are suitable to test this hypothesis. Diversi ty in ecology, coloration and anatomy evolved in these fish faster than pos tzygotic barriers to gene Bow, and little is known about how this diversity is maintained. It was tested whether recognizable forms are selection-main tained morphs or reproductively isolated species by investigating in the fi eld reproductive timing, location of spawning sites, and mate choice behavi our. There was a large interspecific overlap in timing of breeding and loca tion of spawning sites, which was largest in members of the same genus. Beh avioural mate choice of such closely related taxa was highly assortative, s uch that it is likely that they are sexually isolated species and that dire ct mate choice is the major force that directs gene flow and maintains form diversity. The results differ from what is known about recent radiations o f other lacustrine fish groups where speciation seems to be driven by diver ging microhabitat preferences or diverging timing of reproduction, but are in agreement with predictions from models of speciation by diverging mate p references. (C) 1998 The Fisheries Society of the British Isles.