Meeting Abstract
Disease has been attributed to significant declines in populations of ectothermic vertebrates, including the gopher tortoise (Gopherus polyphemus), which is a keystone species native to the southeastern United States. Across ectothermic vertebrates, climatic instability has been suggested to drive patterns of disease susceptibility, as individuals are often most susceptible during periods of thermal instability. The objective of this study was to experimentally test the seasonal lag hypothesis in G. polyphemus, which predicts rapid temperature changes cause a miss-alignment of realized and optimal immune function. We measured one parameter of innate, constitutive immune function, bactericidal ability (BA), in G. polyphemus during seasonal acclimation states of winter dormancy and summer activity. Additionally, we measured BA in winter-acclimated animals (N = 22) exposed for 48 hours to the summer-acclimated temperature (32.5°C) and summer-acclimated animals (N = 17) exposed for 48 hours to the winter-acclimated temperature (12.5°C). We found support for the seasonal lag hypothesis, and that this effect is context dependent on acclimation state. Specifically, we found no effect of the rapid temperature increase on winter-acclimated individuals exposed to 32.5°C (P = 0.325), but we did find a significant reduction in BA in summer-acclimated animals exposed to a rapid temperature decrease (P = 0.040). Results from this study generally support a process by which thermal variability may increase disease susceptibility in ectothermic vertebrates. Specifically, this study highlights the constraints that rapid temperature decreases may impose on individuals acclimated to warm temperatures.
