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

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 of CORT are essential for individuals to manage energy resources and thus cope with negative perturbations such as predation and storms. The benefits of CORT are 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 feather CORT levels, infection status and diversity of haemosporidian parasites in the Blue-crowned Manakin Lepidothrix coronata, considering possible effects related to the sex and age of individuals. We predicted higher levels of feather CORT in infected individuals. We observed that feather CORT levels 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 feather CORT levels were not associated with the infection status and diversity of haemosporidian parasites. That haemosporidian occurrence probability does not increase with elevated feather CORT levels suggests that individuals are not immunosuppressed by elevated levels of this hormone, at least to the extent that feather CORT truly reflects individual differences in the level of this hormone.
The field data collection was based upon research supported by the Conselho Nacional de Desenvolvimento Cientıfico e Tecnologico (UNIVERSAL number 471092/2012-6 Faixa C to M.A.) and by Fundacao de Amparo a Pesquisa do Estado do Amazonas (PRONEX proj. 003/2009, number 653/2009 to M.A. and Albertina Lima). Hormone analysis was funded by Conselho Nacional de Desenvolvimento Cientıfico e Tecnologico (Ciencia sem Fronteiras Chamada No. 71/2013 to M.A., D.G. and Regina Macedo). Haemosporidian laboratory work was funded by NSF DEB-1503804 to J.D.W. During the project, M.B. received a fellowship from Fundacao de Amparo a Pesquisa do Estado do Amazonas (FAPEAM) and Conselho Nacional de Desenvolvimento Cientıfico e Tecnologico (CNPq). A.F. was supported by a postdoctoral fellowship (PNPD scholarship) from Coordenacao de Aperfeicoamento de Pessoal de Nıvel Superior (CAPES).