Activity Metabolism in the Lizard Sceloporus occidentalis

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Abstract
Standard levels of oxygen consumption and oxygen consumption and lactate production during and after burst activity were measured in the iguanid lizard Sceloporus occidentalis. The activity capacity of this animal is restricted; it sustains vigorous movement for only 1-2 min. The contribution of aerobic metabolism to that activity is strongly thermally dependent. Maximal levels of oxygen consumption are achieved during activity at 30-40 C. At lower temperatures, significant lags occur in oxygen uptake, which appear to result from restricted ventilation. The maximum aerobic increase above resting levels occurs at 35 C, preferred body temperature of this species. Repayment of the initial stages of oxygen debt is also most rapid at 35 C. Lactic acid concentration reaches high levels during activity, and its formation is greatest at 30 C. Anaerobic metabolism represents 62%-82% of the energy utilized during burst activity, accounting for nearly all of the carbohydrate catabolized. The combination of energy utilization in both aerobic and anaerobic modes gives Sceloporus its highest activity capacity at 30-35 C, the range of body temperatures normally experienced diurnally by this species throughout the year.