Hormonal Control of Male Reproductive Behaviour in Fishes: A Stickleback Perspective

Abstract

Male three-spined sticklebacks Gasterosteus aculeatus, show pronounced reproductive behaviour including paternal care, and go through a number of nesting cycles during their breeding season. Each nesting cycle consists ofa sexual phase followed by a parental phase. In common with other studied fishes showing parental care, plasma levels of 11-ketotestosterone (llkT) in stickleback males are high during the sexual phase and low during the subsequent parental phase. Gonadectomy-replacement studies have clearly demonstrated that those male reproductive behaviours expressed during the sexual phase, including territoriality, nest-building and courtship, are strongly influenced by androgens, notably 11kT. However, while androgens play an important role in initiating the onset of reproductive behaviour, they appear to play a more permissive role once the males have entered their nesting cycle. More so, present evidence indicates that paternal behaviour such as fanning occurs independent of the androgens. The very high plasma 11kT levels (300-400 ng/ml) observed in male sticklebacks during the sexual phase stimulates both sexual behaviour and the development of the pronounced male secondary characters, notably kidney hypertrophy and spiggin production. In contrast to the three-spined stickleback, male fifteen-spined sticklebacks, Spinachia spinachia, which also exhibit pronounced kidney hypertrophy, show much lower plasma 11kT levels (c. 12 ng/ml) during the nest-building period. This suggests that the unusually high 11kT levels shown by the three-spined stickleback males is not a function of spiggin production alone, and possibly reflects more the pronounced differences in sexual behaviour shown between the two species. While a role for androgens in the control of sexual (courtship) behaviour in the stickleback is unequivocal, further studies are needed to determine the role of other hormones/neuropeptides in the control of parental behaviour.