Dual Threshold Control of Peripheral Temperature in the Lizard Dipsosaurus dorsalis

A mathematical analysis of continuously proportional and neutral zone (dual threshold) temperature regulation leads to criteria for experimentally distinguishing between these differing controls. Colonic, skin, and head temperatures were measured in a lizard as it shuttled between hot and cold environments. An analysis of body temperature when hot-environment temperature was 65 C shows that the lizard was thermoregulating (P < .05). A further analysis of behavior at a hotenvironment temperature of 47 C shows that the body temperatures initiating exit from the hot and cool environments were significantly (P < .05) different. Furthermore, shuttling ceased when cool-environment temperature was increased to 36 C or hot-environment temperature was lowered to 43 C. Therefore, it was concluded (P < .05) that thermoregulation was not single set-point continuously proportional. Our results, when combined with those of field and gradient observations, support a dual stochastic threshold (DST) control hypothesis. Exit skin temperature was unaffected by different hot-environment temperatures; however, as hot-environment temperature was increased exit colonic and brain temperatures decreased linearly, suggesting that peripheral temperature was regulated. We conclude (P < .001) that deep body temperature is not the major directly regulated variable.