Physiological Thermoregulation in the Lizard Dipsosaurus dorsalis

Physiological capacity for altering rates of heat exchange in the iguanid lizard, Dipsosaurus dorsalis, was determined by measuring the rate of temperature change as animals heated from 20? to 38? C and cooled from 40? to 22? C at wind velocities of 0, 90, 200 and 400 ft/min. Rates of heating exceeded rates of cooling by as much as 27% in live animals, while dead animals heated and cooled at the same rate. The percentage increase in the rate of heating was independent of body weight (range: 20-90 g) but was lower at the two highest wind velocities. Maximum rates of endogenous heat production during both heating and cooling could account for 44% of the difference in rate of temperature change at a body temperature of 30? C. The remainder of the difference was attributed to changes in the rate of blood flow between the core and the periphery.