Giant males or dwarf females: what determines the extreme sexual size dimorphism in Lamprologus callipterus?

In the Lake Tanganyika cichlid Lamprologus callipterus, males were >12 times heavier than females, the most extreme sexual size dimorphism in this direction among animals. L. callipterus males construct nests of empty snail shells in which the females breed. If the ancestors of L. callipterus were small cichlids, both sexes may have used shells for shelter. If the ancestors were larger, snail shells could not be used as shelters and would be important only for reproduction. In the field and the laboratory, females bred only in shells and the largest spawned in the largest shells. In the field, females chose larger shells than the average available in males’ territories and did not copy the mate choice of other females. They never hid from predators in snail shells and they occurred commonly in areas without any potential shell shelters. In laboratory experiments females used shells only for reproduction and hardly for shelter. Therefore, it seems unlikely that L. callipterus descended from small shell-brooding cichlids which used shells for shelter, but more likely that the ancestors were of large or intermediate size, and that female size is constrained by the sizes of snail shells, which appear to be optimal breeding substrata. 2000 The Fisheries Society of the British Isles