The influence of bacterial lipopolysaccharide on the thermoregulation of the box turtle Terrapene carolina.

Ectotherms can adjust their thermoregulatory set points in response to bacterial infection; the result may be similar to endothermic fever. We examined the influence of dose on the set point of body temperature (T(b)) in Terrapene carolina. After acclimating postprandial turtles to 20 degrees C, we injected them with two doses of bacterial endotoxin (LPS; lipopolysaccharide from Escherichia coli), 0.0025 or 0.025 mg LPS/g nonshell body mass, or with reptilian saline (control group). We placed the animals singly in linear thigmothermal gradients and recorded their T(b)'s for 48 h. The turtles showed dose-influenced thermal selection. Turtles injected with the high dose had T(b)'s significantly higher than control turtles, whereas low-dose turtles had T(b)'s significantly lower than control turtles. Also, there was a low daily effect on the T(b) of the turtles injected with the high dose. High-dose turtles had significantly higher T(b)'s than the control turtles during the first day but not during the second. Our results support the prediction of Romanovsky and Székely that an infectious agent may elicit opposite thermoregulatory responses depending on quality and quantity of the agent and the host health status.