Socially-induced variation in physiological mediators of parental care in a colonial bird.

International audienceSocial facilitation of reproduction occurs in humans and animals, and may represent one of the bases of reproductionin groups. However, its underlying physiological mechanisms remain largely unexplored. Here, we found ina colonial bird, the Adélie penguin (Pygoscelis adeliae), that the number of parental interactions (nest relief ceremonies)performed by breeding individuals on the colony was positively related to prolactin levels in otherbreeding individuals exposed to these interactions (i.e. focal individuals). As prolactin is typically involved inthe expression of parental behaviour in birds, this suggests that parental interactions by conspecifics representsocial cues that might increase parental motivation in focal individuals. Moreover, parental interactions werenot related to corticosterone levels in focal individuals, suggesting that these social cues were not stressful forpenguins. However, social stimulation still had a cost for focal individuals, as itwas negatively related to their antioxidantdefences (a component of self-maintenance). As social stimulationwas also positively related to prolactinlevels, this highlights the fact that social stimulation acts on the trade-off between reproduction and selfmaintenance.For the first time, the results of the current study shed light on the physiological factors potentiallyunderlying social facilitation of parental care. Importantly, they suggest that, even though social facilitation of parentalcare may increase breeding performance, it can also negatively affect other fitness components