By Kate Sabey, Ezenwa Lab
Wild animals commonly experience trade-offs in their investment among different physiological processes, including reproduction, nutrition, and immune function. In particular, given its importance for pathogen defense, many studies have sought to measure when and why animals modulate their investment in immunity. However, since animals encounter a range of conditions in natural environments, the observation of these physiological trade-offs are likely shaped by a variety of intrinsic and extrinsic factors.
Through her masters thesis research, Ashley explored such context-dependence in immune dynamics. In her first chapter, she examined variation in relationships between testosterone and immunity in free-ranging American alligators, finding that the effects of testosterone on microbial killing depended on levels of co-circulating hormones, the microbe of interest, and temperature. In her second chapter, Ashley further explored relationships between immune performance and temperature across vertebrate species, finding that the effects of temperature on immune performance depended on host thermoregulation strategy. For example, ectotherms experienced trade-offs between immune performance at the host’s optimal temperature and the consistency of immune performance across temperatures, but these trade-offs were absent in endotherms. Together, Ashley’s work emphasizes the importance of considering both intrinsic and extrinsic variation when assessing the immune performance of wild vertebrates. Importantly, accounting for this context-dependence will be crucial in understanding the relevance of physiological trade-offs across animal systems.