Meeting Abstract
Physiological function, and specifically immunological function, in ectothermic vertebrates is often constrained by thermal environments that may negatively affect performance. North American tortoises (genus Gopherus) have been the source of numerous studies investigating baseline immunological parameters (specifically related to upper respiratory tract disease, URTD), yet little is known regarding the nature of acute immune responses and how immune responses are constrained by thermal environments in this taxon of high conservation concern. Herein, we measured immune responses in gopher tortoises (Gopherus polyphemus) to simulated acute bacterial infection (lipopolysaccharide, LPS). We performed assays in G. polyphemus that had been acclimated to two different seasonal (and thus thermal) acclimation states of winter and summer to test the hypothesis that seasonal context determines the scope of an immunological response. We measured body temperature, bactericidal ability (BA), plasma iron, total and relative circulating leukocyte proportions, and baseline corticosterone in response to LPS injection in tortoises acclimated to winter and summer conditions. We found that LPS caused a significant increase in BA and the number of circulating heterophils, and a decrease in plasma iron. However, we did not find that G. polyphemus increased their set body temperature, a pattern which would be consistent with behavioral fever. The lack of behavioral fever in this species is similar to earlier studies in testudinids in which tortoises were not shown to increase body temperature in response to acute infection. In general, we found that the immune responses were not affected by seasonal acclimation state, and that both winter- and summer-acclimated tortoises generated significant immune responses to LPS.
