PARENTAL CARE AND THE PROLACTIN SECRETION PATTERN IN THE KING PENGUIN- AN ENDOGENOUSLY TIMED MECHANISM

The King penguin (Aptenodytes patagonicos) has been studied on Possess ion Island, Crozet Archipelago (46 degrees 25'S-51 degrees 45'E). It i s an offshore feeder, but it breeds on land. Its breeding cycle is unu sually long (about 14 months). It starts at the beginning of spring, i s interrupted during 5 months of winter, and ends in the next spring. Furthermore, it is characterized by a long parental care period, of ab out 11 months, including the winter interruption. In fact, care given to the egg and the chick is biparental, which supposes that parental b ehavior includes both parents. Each parent alternates care given to th e egg and to the chick on land and foraging bouts at sea. An incubatio n bout, or a chick care bout, is called a shift. Prolactin is the hypo physeal hormone known to be correlated with incubation and chick care. We studied the mechanism of the maintenance of prolactin during the p arental care period in the King penguin, a period which is unusually l ong. In many species, prolactin secretion has been shown to be stimula ted by the presence of eggs and/or chicks, but in the King penguin, pr olactin secretion is observed throughout the entire period of parental care, despite the fact that the birds leave the egg and the chick rep eatedly and for extended periods of time to feed. Prolactin levels ris e significantly at the beginning of courtship; females have significan tly higher prolactin levels than males during courtship, copulation, a nd the period of waiting for egg laying. In both sexes, prolactin leve ls remain high during incubation and the first part of chick rearing, before winter. Prolactin concentrations decline somewhat during the wi nter period of minimal parental care, but remain that level in spring when parental care starts again. The level returns to basal value duri ng molt. Prolactin levels rise during the incubation shifts but not ov er the course of contact with young. Prolactin values remain high in u nsuccessful breeders, possibly preventing the birds from relaying, but remain low in immature birds. These data raise questions about how pr olactin secretion is controlled in this species. The hypothesis of a p rogrammed secretion of prolactin is advanced. (C) 1996 Academic Press, Inc.