Role of 11-ketotestosterone and prolactin in the control of reproductive behaviour in the male three-spined stickleback, Gasterosteus aculeatus

Sammanfattning: The male three-spined stickleback, Gasterosteus aculeatus, builds a nest by glueing plant material together using an 11-ketotestosterone (11kT) induced protein (spiggin) secreted from the kidney. When females have been induced to lay eggs in the nest, male sexual (zigzag) behaviour decreases and parental care (fanning) increases. The overall aim of this thesis was to investigate the hormonal background to the changes in reproductive behaviour and to the possible changes in the secondary sexual character - the kidney, over the male stickleback nesting cycle. The main focus has been on 11kT and the following three major questions have been addressed: a) How do hormones, particularly circulating 11kT, change during the male stickleback nesting cycle? b) Are changes in hormones, particularly 11kT, related to changes in kidney size and spiggin production during the nesting cycle? c) Are changes in 11kT and PRL responsible for the changes in reproductive behaviour during the nesting cycle?Plasma 11kT levels were measured using radioimmunoassay and were found to be c. 30 times higher during the sexual phase (in nesting, non-spawned males) than at the end of the paternal phase (in spawned males). Males that spawned three or more times showed a decline in 11kT levels and a cessation in zigzags, which both occurred earlier than in males that only spawned once. Compared to non-spawned males, kidney size and spiggin-mRNA levels decreased and glueing behaviour eventually ceased in spawned males, consistent with the decrease in 11kT levels following spawning. Castration removed 11kT, while androgen replacement using Silastic® implants prevented the natural decline in 11kT levels in spawned fish. Fanning remained low and zigzags were present in all non-spawned treatments, regardless if being sham-operated, castrated or castrated/androgen treated. However, zigzags did eventually decline in castrated non-spawned males, but later and to a far lesser extent than in all spawned treatments (as above). In all spawned treatments there was a decline in zigzags and an increase in fanning. In castrated spawned males, however, the decline in zigzags came earlier than in the other spawned treatments. PRL injections stimulated fanning in nesting, non-spawned sticklebacks, while zigzags decreased following salmon PRL treatment. However, the behavioural changes following PRL injections were far smaller than the natural changes that occur in the presence of eggs.Since androgen treatment did not prevent the decline in zigzags/increase in fanning in spawned males, the natural decline in 11kT cannot be responsible for the main part of the behavioural changes over the nesting cycle. The limited effects of castration in non-spawned fish also exclude other gonadal hormones from being responsible for most of these changes. The drastic decrease in 11kT levels during the later parental phase could, however, result in an energy-saving decrease in spiggin-production, when this is no longer needed. A more probable mechanism by which the eggs regulate the changes in reproductive behaviour over the nesting cycle involves PRL. However, since the behavioural changes in nesting, non-spawned fish following PRL injections were comparatively small, there is likely to be other factors besides PRL levels alone that are responsible for the behavioural changes over the nesting cycle.