Active accumulation of spawning substrate : a determinant of extreme polygyny in a shell-brooding cichlid fish

Abstract Abstract. Observations on the reproductive behaviour and polygynous mating system of an endemic shell-brooding cichlid fish, Lamprologus callipterus , revealed that territorial males actively transported and accumulated spawning substrate (empty gastropod shells) to make nests. In contrast to conventional resource defence polygyny, males of this species can therefore create a defensible resource distribution. Females successively visited the nests, chose one shell, spawned the whole clutch inside the shell and stayed inside until the young became independent. Males were freed from direct parental care but defended the territory. Nest usurpation by larger males and frequent shell stealing among males were observed; these resulted in cannibalism of the young fathered by the former males. Large males accumulated more shells and consequently monopolized more females than did smaller males. Maximum size of females was apparently limited by the size of available shells, resulting in extreme sexual dimorphism. Extreme polygyny in this species, associated with intense intra-sexual competition and extreme sexual dimorphism, was based mainly on transportability of spawning substrate and the specific behavioural competence of males to use it.