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Abstract
Immunity is a physiological process crucial to survival. Thus, identifying factors influencing immunity is important for understanding variation in an organism’s fitness across contexts. In this thesis, I used microbial killing assays to examine temperature and hormonal drivers of immune performance across vertebrates. First, by testing testosterone-immunity relationships in alligators, I found that interactions with co-circulating hormones and temperature may be important mediators of testosterone-immunity trade-offs. Second, by assessing immune performance of endotherms and ectotherms across temperatures, I found that immune performance across temperatures depended on thermoregulatory strategy and that thermoregulatory strategy determined whether temperature imposed trade-offs on immunity. Third, I showed that variability in immune performance depended on microbial context, with the presence of testosterone-immunity tradeoffs and temperature-dependent shifts in immune performance varying across the different microbes used to quantify immune performance. In aggregate, this work provides insights into immunological trade-offs and intrinsic and extrinsic factors influencing these trade-offs.