Fasting-induced changes of immunological and stress indicators in breeding female eiders

One adaptive significance of immunosuppression during reproduction can be explained by the immunopathology-avoidance hypothesis. This hypothesis states that since heat shock proteins (HSP) are highly conserved proteins found in both pathogen and host, and are expressed at a higher level during reproduction, the risk of autoimmunity is then increased, HSP being the target of the host's immune response. Reduced immunocompetence has been attributed to hormonal regulation, in particular by glucocorticoids. The current study aimed at testing the immunopathology-avoidance hypothesis and the implication of corticosterone in incubating fasting common eiders (Somateria mollissima). To this end, we have measured immunological and stress indicators including immunoglobulin (IgY), HSP70, HSP60, and corticosterone levels in breeding females. A multivariate general linear model analysis showed that female body condition, IgY, HSP70, and HSP60 levels were the main variables explaining the model. Females showed a significant decrease by 15% of their IgY index during incubation. Conversely, HSP70 and HSP60 levels significantly increased by 12 and 10%, respectively throughout incubation. Moreover, there was a positive significant relationship between both HSP whereas HSP60 levels were negatively correlated to IgY index. Plasma corticosterone levels showed a tendency to decrease during incubation. We conclude that these findings are consistent with the immunopathology-avoidance hypothesis in breeding eiders. Nevertheless, the long-term reproductive costs and the underlying mechanisms of such an immunosuppression remain to be determined and will require further experiments.