Sexual Dimorphism in Lamprologus Callipterus
Lamprologus callipterus is one of over 300 species of cichlid (a freshwater fish) found only in Lake Tanganyika in Africa. Most African cichlids, including L.callipterus , exhibit sexual size dimorphism-the males are larger than the females. What is unusual about L. callipterus is the magnitude of the size difference. The key to understanding the sexual dimorphism of L.callipterus lies in the reproductive behavior of the species, particularly spawning (release of eggs by females and release of sperm by males) and brooding (protection of eggs). Female L.callipterus spawn and brood their eggs in empty snail shells on the lake bottom. In all other shell-brooding cichlids, both sexes enter the shell to spawn and thus both must be small enough to fit into the shells available on the lake bottom. In L. callipterus , however, only the females enter the shell to spawn and brood their eggs. The males remain outside, releasing their sperm only at the entrance to the shell. Consequently, female L. callipterus are small enough to fit into the shells, but the males, unconstrained by the need to enter shells, are much larger.
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