Seasonal and Fasting-Related Changes in Circulating Gonadal Steroids and Prolactin in King Penguins,Aptenodytes patagonicus

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Abstract
Temporal correlations between reproductive endocrinology and the breeding and molt cycle of the king penguin were studied at the Crozet Islands, in the southern Indian Ocean. This species is unique in having a long cycle (14-15 mo), mainly due to a prolonged fledging period (11 mo), which includes the austral winter. Plasma gonadal steroids and prolactin were at their minimum levels during the prebreeding molt. However, circulating testosterone (males) and estradiol and progesterone (females) were already elevated at the time of arrival at the colony to breed, and the levels peaked during copulation. After laying plasma steroids decreased but remained above basal levels during the following months. Prolactin was low during the sexual phase of the reproductive cycle of both males and females. It reached high plasma concentrations in incubating birds and remained elevated during the whole fledging period. Possible roles for sustained high prolactin levels in winter and spring, which involve the care of the single chick and the prevention of a new cycle, are discussed. The effect of nutritional status of birds on plasma reproductive hormones was also investigated in relation to brief (brooding shifts) and prolonged (incubation spells)fasting. No major effect of food deprivation on plasma hormones was found in incubating and brooding king penguins during normal shifts. However, birds with a low body mass (<9 kg), which progressively mobilized their body protein, presented higher progesterone levels and lower plasma testosterone and prolactin. The decrease in plasma prolactin may be involved in the spontaneous abandon of reproduction previously described in penguins that have depleted their fat stores.

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