Influence of Chemical Receptivity On Reproductive Behaviour of the Male Three-Spined Stickleback (Gasterosteus Aculeatus L.)

AbstractThe present investigation is concerned with chemoreceptivity in the male three-spined stickleback (Gasterosteus aculeatus L.) during reproductive behaviour. The functions of cranial nerves were studied with regard to nest building (N), the increase in the zigzag dance (a measure of the sexual tendency (S)) between N and the day of fertilization (F) of the eggs, the zigzag dance between F and the day of hatching (H), suppression of the zigzag dance (if still present) at H, and fanning activity (P) during these days of a reproductive cycle (F-H). The methods of quantifying S and P, as well as the methods of sectioning the olfactory nerves and the branches of cranial nerves possibly involved in the conduction of chemical stimuli are described. The behavioural changes observed after sectioning the olfactory nerves, branches of cranial nerves or combinations of these nerves are compared with behavioural data of unoperated fish. Special attention is given to behavioural changes following regeneration of transected nerves. Nest building is still possible after sectioning of the olfactory nerves, but occurs only in a few fish. The functioning of the olfactory nerves might influence the development of nest building behaviour by inducing hormonal changes, necessary to start such reproductive activities. During the period between N and F (the latter determined by the observer), the number of zigzags (S) increases from zero up to 100 or more per 5 minutes. The olfactory nerves are indispensable for the promotion of sexual behaviour during this period. It seems likely that these nerves are necessary to induce hormonal changes in such a way that the reproductive cycle can proceed from nest building to courtship stage. In the exceptional case that a nest was built by a fish in which the olfactory nerves had been sectioned, the zigzag score remaining low, all other reproductive activities still occurred, including fertilization. Fanning activity in such fish appeared to be quantitatively normal. When the olfactory nerves were sectioned between N and F, at a stage when the zigzag scores had reached an essential level ( 100 per 5 min), both sexual and fanning activity between F and H were normal. This is explained by the supplementary functioning of both the ramus posttrematicus IX and the ramus pretrematicus X1. Both eggs and embryos stimulate sexual behaviour between F and H. The olfactory nerves exert an exciting function with regard to sexual behaviour during th