Parental care and the prolactin secretion pattern in the King penguin: an endogenously timed mechanism?

The King penguin (Aptenodytes patagonicus) has been studied on Possession Island, Crozet Archipelago (46 degrees 25'S-51 degrees 45'E). It is an offshore feeder, but it breeds on land. Its breeding cycle is unusually long (about 14 months). It starts at the beginning of spring, is interrupted during 5 months of winter, and ends in the next spring. Furthermore, it is characterized by a long parental care period, of about 11 months, including the winter interruption. In fact, care given to the egg and the chick is biparental, which supposes that parental behavior includes both parents. Each parent alternates care given to the egg and to the chick on land and foraging bouts at sea. An incubation bout, or a chick care bout, is called a shift. Prolactin is the hypophyseal hormone known to be correlated with incubation and chick care. We studied the mechanism of the maintenance of prolactin during the parental care period in the King penguin, a period which is unusually long. In many species, prolactin secretion has been shown to be stimulated by the presence of eggs and/or chicks, but in the King penguin, prolactin secretion is observed throughout the entire period of parental care, despite the fact that the birds leave the egg and the chick repeatedly and for extended periods of time to feed. Prolactin levels rise significantly at the beginning of courtship; females have significantly higher prolactin levels than males during courtship, copulation, and the period of waiting for egg laying. In both sexes, prolactin levels remain high during incubation and the first part of chick rearing, before winter. Prolactin concentrations decline somewhat during the winter period of minimal parental care, but remain that level in spring when parental care starts again. The level returns to basal value during molt. Prolactin levels rise during the incubation shifts but not over the course of contact with young. Prolactin values remain high in unsuccessful breeders, possibly preventing the birds from relaying, but remain low in immature birds. These data raise questions about how prolactin secretion is controlled in this species. The hypothesis of a programmed secretion of prolactin is advanced.