No Effect in Plasma Corticosterone Levels After Observation of Diseased Conspecifics

Organisms commonly respond to stressors in their environment by increasing the secretion of corticosterone (CORT). While increased CORT is acknowledged as a response to predation risk by organisms inhabiting a landscape of fear, new research raises the potential for changes in CORT as a response to the risk of infection by organisms in their environment. An increase in CORT of a healthy, uninfected individual in response to their perception of the risk of infection in their environment could change their susceptibility to infection, highlighting a significant role for CORT to alter host-pathogen dynamics. To investigate the effects of infection risk on host CORT levels, we conducted an experiment where healthy domestic canaries (Serinus canaria) observed canaries either infected with Mycoplasma gallisepticum (MG), which present behavioral and visual symptoms of infection, or symptom-free, sham-infected controls. We measured CORT from blood samples collected after either long-term (6 days) or short-term (1 h) observation of MG or sham-infected individuals. We found no difference in CORT levels between observers of MG or sham-infected birds at either time point, with the limitation of small sample size in the short-term observation (12 birds). We suggest further research should investigate changes in CORT at finer scales to ensure a complete picture of CORT profiles in response to infection risk.