Thermal biologists often investigate the thermal properties of physiological processes using thermal performance curves (TPCs). However, these studies have largely been conducted on endothermic organisms which maintain stable, warm body temperatures, and the effects of body temperature on critical physiological processes, like immune function, have been understudied. In ectotherms, body temperature directly reflects that of their environment, and physiological performance, from a molecular to whole organism scale, is highly influenced by the temperatures they experience. Knowing this, we posed two hypotheses: (1) TPCs for immune function would vary between summer and winter- active ectotherms due to seasonal acclimation, and (2) TPCs would vary between a subtropical (pygmy rattlesnake) and temperate (northern water snake) ectotherm species, due to variation in thermal environments experienced at different latitudes. To examine this, bacteria killing ability (BKA) assays were performed on two species of snake to assess the function of complement proteins and natural antibodies in the innate immune system when exposed to a gram negative bacterium, E.coli. Resulting BKA scores were compared across a range of temperatures (10-45℃), after which nonlinear curves were constructed to describe thermal performance of immune function in each species and season. Results indicated that thermal effects on immune function were different in summer compared to winter pygmy rattlesnakes. However, there was no statistical support for the hypothesis that differences in latitude affect the thermal performance of immune function. These results suggest that seasonal acclimation in the thermal performance of immune processes should be explored further in
future studies.