Physiological responses of the lizard Sauromalus obesus to changes in ambient temperature.

CRAWFORD, EUGENE C., JR., AND GEOFFREY KAMPE. Physiological responses of the lizard Sauromalus obesus to changes in ambient temperature. Am. J. Physiol. 220(5) : 12561260. 197 1 .-Animals were subjected to ambient temperatures from 26 to 43.5 C. Body temperatures remained 0.2-O. 7 C above ambient. Cutaneous evaporation increased from 2.0 to 9.5 mg HaO/cmz.day, with a & of 2.43. Respiratory evaporation increased with a & of 3.96 to 40 C (from 1.3 to 8.0 mg HsO/g l day). Between 40 and 43.5 C, respiratory evaporation increased abruptly to 38 mg HzO/g . day. A change in respiratory pattern was associated with the increase in respiratory evaporation. The mouth opened, tidal volume decreased to one-third its initial value, respiratory rate increased 5 times, and pulmonary ventilation doubled. At 43.5 C 45% of the metabolic heat production was dissipated by respiratory evaporation and 66a/, was dissipated by total evaporation. The thermal conductance of 1 cal/cm2= hr. OC is about 3 times that of mammals of comparable size. The respiratory pattern is similar to that observed in panting homeotherms.