How does corticosterone affect parental behaviour and reproductive success? A study of prolactin in black-legged kittiwakes
Résumé
1. An emergency life-history stage is expressed in breeding vertebrates when the immediate survival is threatened by poor energetic conditions (i.e. allostatic overload). This emergency life-history stage shifts energy investment away from reproduction and redirects it toward immediate survival. 2. In birds, this emergency life-history stage is promoted by a release of the stress hormone corticosterone. However, how corticosterone reduces the expression of parental cares remains to be clarified. One hypothesis is that the release of corticosterone may also affect prolactin levels, a pituitary hormone widely involved in regulating parental behaviours. 3. We tested this hypothesis by experimentally increasing corticosterone levels of chick-rearing black-legged kittiwakes ( Rissa tridactyla ) over a 2-day period and by monitoring prolactin levels over an 8-day period. We also investigated whether this hormonal manipulation affected nest attendance, the motivation to come back to the nest after a short-term stress and breeding success. 4. Corticosterone treatment resulted in a significant increase in plasma corticosterone levels during the first 2 days, which returned to pre-treatment values at day 3. This short-term corticosterone increase was accompanied by a 30% decrease in prolactin levels. Prolactin levels were reduced in a progressive and persistent manner and did not return to their initial levels when corticosterone levels returned to pre-treatment levels. Moreover, although corticosterone levels had returned to pre-treatment values, low prolactin levels were associated with a reduced nest attendance and a greater latency to come back to the nest after a short-term stress. This hormonal treatment also significantly reduced breeding success. 5. This experimental treatment strongly supports the idea that the secretion of these two hormones might be mechanistically linked. Thus, we showed that even a relatively short-term increase in corticosterone levels can durably affect plasma prolactin levels. Therefore, the well-established suppressive action of corticosterone on parental behaviour is probably mediated and reinforced through an effect on prolactin levels. This study highlights the need to consider the potential synergistic effects of these two hormones when studying on the hormonal basis of parental decisions.