Repeatable behavioural and immune defence strategies against infection are not traded off

Abstract

Disease exposure is a threat to all organisms, but there are a number of methods of self-defence. First, individuals can proactively prevent disease through avoidance behaviours. If they become infected, individuals can activate an immune response to control the infection. A trade-off between avoidance behaviours and immune response activation has been hypothesized to occur because of costs associated with each strategy. Individuals may balance behavioural and immunological strategies to provide optimal protection against disease. To test this hypothesis in a captive population of zebra finches, Taeniopygia guttata, we conducted behavioural trials to determine how much time focal birds associated with stimulus birds that were either healthy or displayed sickness behaviours. We then inoculated focal birds with lipopolysaccharide (LPS) and measured levels of natural antibodies, complement and haptoglobin. One physiological mechanism that may mediate the proposed trade-off between behavioural and immunological defences is the glucocorticoid hormone corticosterone (CORT). Therefore, we experimentally manipulated CORT in another subset of birds. Finally, it is unknown whether individuals are consistent in their strategy choice over time or whether strategy choice changes based on environmental context or life history stage. Thus, we tested behavioural and immunological responses multiple times. We found limited evidence that zebra finches trade off between behavioural avoidance and immune responses as protection against infection, instead these defences were unrelated or positively correlated in control birds. CORT changed the relationships between behavioural and immunological defences and these defences were traded-off after acute CORT exposure. Some behavioural and immunological defences were repeatable over three months. Thus, even though individuals may be consistent in behavioural and immunological defence strategies, these defences are not generally traded off. Further research is encouraged to determine whether behavioural and immunological trade-offs persist across contexts, life history stages, or in wild populations, and the degree to which strategies are influenced by selection.