Thermoregulatory Set Points of the Eurythermic Lizard Elgaria multicarinata

Abstract

The lizard Elgaria multicarinata exhibits extremely variable body temperatures during ac- tivity (eurythermy). I used operant conditioning to investigate whether this lack of thermoregulatory precision could be attributed to some aspect of the underlying thermoregulatory mechanism. Estimates of upper and lower set point temperatures (USP and LSP, respectively) were obtained by allowing lizards to control the activation of an overhead heat lamp for thermoregulation in an otherwise cool environment. The influence of shelter availability on thermoregulatory behavior was examined by observing lizards with and without a shelter available under the heat lamp. When a shelter was available for the lizard to hide in under the lamp while heating, USP was estimated to be 33.1 (?0.46 SE) C, and LSP 26.0 (?0.62) C, for a difference of 7.1 C. When no such shelter was available, USP was 31.1 (+0.75) C and LSP 25.0 (+0.55) C, for a difference of 6.1 C. The average standard deviation for each set point within individuals was 1.75 for USP and 2.33 for LSP with a shelter available, and 1.31 for USP and 3.15 for LSP when the shelter was not available. These values indicate minor effects of varying levels of exposure while basking, most notably slight declines in set points. The most important finding of the study was that the thermoregulatory set points for E. multicarinata are similar to those estimated for lizards having much narrower ranges of field body temperatures (stenotherms). My findings did not support the hypothesis that the variance in field body temperatures observed for E. multicarinata is largely attributable to an imprecise thermoregulatory mechanism, either due to a large difference between USP and LSP, variation between individuals in the value of either set point, or the poor definition of the set points at the individual level. Instead, the eurythermy observed for this species must be due to responses to one or more proximate environmental conditions.