Effect of Temperature on Metabolism during Running in the Lizard Uromastix aegyptius

Oxygen consumption of the lizard Uromastix aegyptius was determined at body temperatures of 35, 38, and 42 C, while the lizard ran on a treadmill for 10 min at speeds of 0.5-1.5 km·h⁻¹. Oxygen consumption increased linearly with running speed as the lizard doubled its speed from 0.5 to 1.1 km·h⁻¹ (fig. 1). At this speed range no significant difference in oxygen consumption was found when the lizards ran at 35, 38, or 42 C. When the running speed increased from 1.1 to 1.5 km·h⁻¹, V̇o, did not increase at TB of 35 or 38 C. However, when TB was 42 C, V̇o2 increased with this increase in speed. The highest V̇o2 was observed in lizards running at 1.5 km·h⁻¹ at a TB of 42 C. The V̇o2 remained elevated above pre-run levels for long periods (20-40 min) after the lizards stopped running (fig. 2). This was assumed to represent a repayment of an oxygen debt acquired during the run. The contribution of the oxygen debt to total metabolic power (O₂ consumption during the run plus repayment of the oxygen debt) was significant. There was no difference in its contributions at any speed when TB was 35 or 38 C. The contribution of the repayment of the oxygen debt to total power was 2-3 times greater when TB was 42 C (fig. 3). Two types of locomotion were used alternately by the running Uromastix (fig. 4). The switch point between the gaits depends on both body temperature and running speed (fig. 5). The higher the temperature the lower is the running speed at which the lizard changes its locomotion type.