Thermal performance and acclimatization of a component of snake (Agkistrodon piscivorus) innate immunity.

Complement-an immune protein cascade involved in pathogen lysis-was discovered as a temperature-labile component of vertebrate plasma, yet since that time the thermal performance of complement has not received much attention from a comparative or ecological perspective. We investigated two thermal hypotheses involving the complement system of the cottonmouth snake (Agkistrodon piscivorus). We tested whether complement performance would conform to optimal thermal reaction norms commonly observed in ectotherm ecophysiological studies, predicting that complement efficiency would be maximal at or near the cottonmouth's field body temperatures. We also tested thermal acclimatization of complement performance, by comparing temperature/performance curves from samples collected in three different seasons. Complement efficiency exhibited the same significant positive correlation with temperature in all three seasons. This seasonally invariable temperature-performance relationship may allow easy acquisition of behavioral fever, as well as trade-offs between immune performance and energy balance, ultimately endowing snakes with immunological flexibility not available to endotherms.