Authors

Discussion

Parasite infections are generally considered ‘stressful’ to their vertebrate host species, although the role of parasites as a physiological stressor is unclear. Stress hormone responses of vertebrates to parasites appear contradictory in the literature, hence, our overall aim in this study was to assess variation in stress hormone responses across vertebrate species, with a focus on glucocorticoid responses following experimental infections. Our meta-analysis encompassed 31 parasite species, 32 host species, and 146 effect sizes. We found that glucocorticoids in the infected groups, relative to the control groups, showed an overall increase in response to parasite infection, when based on the largest effect size observed for studies with single and multiple samples taken. We next investigated the effect of time since infection on the glucocorticoid response using those studies that had multiple glucocorticoid measurements for varying time periods following infection. Glucocorticoids are associated with important anti-inflammatory responses and increasing glucocorticoids following experimental infections would demonstrate an acute stress response to parasite infection in vertebrates in general, but this relationship could change under the chronic stress possibly imposed by some parasite infections. Furthermore, we present results showing that glucocorticoid responses following the time course post infection appears to depend on the type of parasite considered.