Factors Affecting Plasma Concentrations of Prolactin in the Common Eider Somateria mollissima
Résumé
In the common eider only the females incubate while they fast for 25 days. Thus, since they rely entirely on their body reserves for successful incubation, they can be defined as capital incubators. To assess the po-tential effects of their initial body mass, the incuba-tion duration, and depletion in body reserves on pro-lactinemia, blood samples of eiders were analyzed during the breeding cycle and an experimental manipulation of the duration of incubation. Levels of circulating prolac-tin increased at the onset of incubation and then reached a high and stable level during incubation before increas-ing sharply before hatching. The prolactin level de-creased significantly upon hatching. Captive females de-prived from their eggs exhibited a rapid decrease in prolactinemia, suggesting that egg stimuli are necessary to prolactin secretion. Aunts, i.e., helper females caring for conspecific young, presented prolactin levels higher than nonbreeding captive females but not significantly different from those of females at hatching. Plasma pro-lactin at hatch was directly related to body mass loss. Birds with shortened incubation have higher body masses and showed higher levels of prolactinemia at hatching than the control group, in accordance with the idea that circulant prolactin at hatching is linked to body condition. Females which underwent an extended incu-bation (and started to eat again) displayed a low body mass and a high prolactinemia. These data therefore sug-gest that refeeding, albeit increasing the risk of preda-tion, enhances prolactin secretion and allows the bird to continue incubation despite that it has reached a poor body condition.