Seasonal changes in oxygen consumption and body composition of Sceloporus occidentalis

Abstract

1. 1. Oxygen consumption in the iguanid lizard Sceloporus occidentalis was recorded every hour at 25°C for at least 3 consecutive days by a coulometric technique, the principle of which is discussed. 2. 2. Metabolic data of 154 male and female lizards captured at 150 and 1500m in the Central Sierra Nevada of California are reported. Data on body composition were obtained from 489 lizards captured at 150m. 3. 3. All lizards displayed circadian changes in oxygen uptake whether placed in continuous darkness or light; the daily metabolic patterns were unimodal during spring and fall, but became bimodal in summer. 4. 4. Regardless of elevation, minimum oxygen consumption bears the same power function to body mass in both sexes, with mass exponent equal to 0.67 ± 0.03. 5. 5. Minimum oxygen consumption, expressed per body mass to the power 2 3 , displayed seasonal changes (32%) with a peak in May–June and a low level in fall. These changes appear to reflect a true metabolic phenomenon rather than only changes in body mass or composition. 6. 6. The allometric relations between body mass, fat-free dry mass, body water, fat and snout-vent length are reported. 7. 7. Body mass and body composition at constant snout-vent length display seasonal changes.