Aerobic and anaerobic metabolism during activity in the lizard Dipsosaurus dorsalis

Summary. 1. Oxygen consumption and lactate content of the lizard Dipso-saurus dorsalis were determined under standard conditions and for a bout of maximal activity induced by a 2-min period of electrical stimulation. Observations were made between 25 ~ and 45 ~ C. 2. Maximal aerobic scope, 2.27 cm a 02/(g • occurred at 40 ~ (Figs. 2, 4). The increase in oxygen consumption during activity at the various temperatures between 25 ~ and 45 ~ represented 7- to 17-fold of corresponding resting levels. 3. Lactate content of resting Dipsosaurus i independent of temperature and averages 0.25 mg/g body weight. Maximal lactate production during the activity induced by a 2-rain period of electrical stimulation occurred at 40 ~ (Fig. 3). The capacity of Dipsosaurus for anaerobic metabolism exceeds that of other lizards investigated, both in its magnitude and in its thermal dependence. 4. The total amount of energy mobilized by Dipsosaurus in the activity induced by a 2-min period of electrical stimulation was maximal at 40 ~ (Fig. 4). An-aerobiosis accounts for a minimum of 58-83 % of the total energetic expenditure. 5. It is postulated that the principal physiological daptations to preferred thermal evels in reptiles have involved energy mobilization during and rapid recovery after activity