A test of the effects of androgens on immunity: no relationship between 11-keto testosterone and immune performance in bluegill sunfish (Lepomis macrochirus)

The posited immunosuppressive effects of androgens are a key component of the immunocompetence handicap hypothesis (ICHH). My thesis uses bluegill sunfish (Lepomis macrochirus) to test two predictions arising from this hypothesis: (1) natural concentrations of the androgen 11-keto testosterone (11-KT) will be negatively related with immunity, and (2) an immunochallenge will lower 11-KT concentration. I found no evidence for a relationship between natural 11-KT concentration and measures of immunity (leukocyte counts, respiratory burst, cytokine gene expression), and an immunochallenge with Vibrio vaccine did not affect 11-KT concentration. I performed a meta-analysis of immunochallenge studies to help interpret my results, and report evidence suggesting that immunochallenges have weaker effects on androgens in fishes compared to other vertebrates. These results suggest that the ICHH may not apply to all vertebrates, though it remains premature to state which factors specific to fish may account for the weaker evidence in favour of immunosuppressive androgens.