Individual variation in feather corticosterone levels and its influence on haemosporidian infection in a Neotropical bird

Abstract

Corticosterone (CORT) is the main glucocorticoid hormone of amphibians, reptiles, birds and some mammals. This hormone may have evolved as an adaptive metabolic mechanism, in part because increased concentrations ofCORTare essential for individuals to manage energy resources and thus cope with negative perturbations such as predation and storms. The benefits ofCORTare offset by costs, because elevated levels can suppress inflammatory responses of individuals, making them more susceptible to parasites and pathogens. In this study, we investigated the relationships between featherCORTlevels, infection status and diversity of haemosporidian parasites in the Blue‐crowned ManakinLepidothrix coronata, considering possible effects related to the sex and age of individuals. We predicted higher levels of featherCORTin infected individuals. We observed that featherCORTlevels were similar among individuals of different sexes and ages. Although haemosporidian infection status did not vary among sexes, occurrence probability was higher among younger individuals, which may indicate that the less developed immune system of these individuals makes them more susceptible to avian malaria. Contrary to expectations, we found that featherCORTlevels were not associated with the infection status and diversity of haemosporidian parasites. That haemosporidian occurrence probability does not increase with elevated featherCORTlevels suggests that individuals are not immunosuppressed by elevated levels of this hormone, at least to the extent that featherCORTtruly reflects individual differences in the level of this hormone.