THE ENDOCRINE BASIS OF THE REPRODUCTIVE-CYCLE IN THE KING PENGUIN (APTENODYTES PATAGONICUS)

What is the breeding frequency of the king penguin? More than 30 years of study and five major investigations, did not answer this question owing to the length (14 months) and the spreading (four months of layi ng) of reproductive events. Following intensively during three consecu tive years nearly 1000 tagged birds in a small colony, we obtained the individual history of a large part of the population. To these demogr aphic and phenological studies, we have associated an endocrinological study validating blood samples and experiments in another colony. The success or failure of a breeding cycle determines the timing of the s ubsequent breeding attempt. At Crozet Islands, the king penguin can re ar one chick every two years at best: a successful breeding is Followe d by unsuccessful late breeding (or by non-breeding). So a large part of the population displays an annual periodicity of breeding attempts but with low individual breeding success. The restarting of the reprod uctive cycle appears basically to be annual, the pituitary responding to the photoperiod. Steroid patterns present classical variations df l evel according to the reproductive stage. Prolactin (PRL) and luteiniz ing hormone (LH) are antagonists but, in this species, PRL remains hig h without external stimulation. To relay after failure in the field, w e have experimentally to break down endogenous PRL. So, we have demons trated that PRL has a key role in the reproductive cycle. Paradoxicall y, the king penguin is an irregular breeder, quasi-biennial, although physiologically an annual breeder. In winter, there is not enough food at sea to rear the chick and during four months, the chick fasts. So a successful breeding cycle, which can be shortened to only nine month s in captivity, is extended to more than a year for ecological reasons .