Activity and oxygen consumption during hypoxic exposure in high altitude and lowland sceloporine lizards

Summary

Resting rates of O₂ consumption$\dot V_{O_2 }$ against$P_{O_2 }$, exercise endurance times and$\dot V_{O_2 }$ during recovery from vigorous exercise were measured inSceloporus occidentalis captured near sea level and inS. graciosus captured above 2850 m. Oxygen consumption against$P_{O_2 }$ was also measured inS. occidentalis captured above 2850 m. When$\dot V_{O_2 }$ was recorded continuously, as ambient$P_{O_2 }$ was slowly reduced from 155 Torr, it became directly dependent upon ambient$P_{O_2 }$ between 110 and 120 Torr. The critical$P_{O_2 }$ for the high altitude lizards was lower than that for the lowland lizards, which enabled the former to maintain relatively higher$\dot V_{O_2 }$ 's when ambient$P_{O_2 }$ was reduced below 120 Torr. The high altitude lizards also had significantly greater endurance when stimulated to exercise at 1600 m ($P_{O_2 }$∼130 Torr). Both the higher$\dot V_{O_2 }$ under hypoxia and the greater endurance roughly parallel a significantly greater maximum$\dot V_{O_2 }$ in the high altitude lizards. At a simulated altitude of 3600 m ($P_{O_2 }$∼100 Torr), maximum$\dot V_{O_2 }$ and rate of recovery of the O₂ debt calculated from post active$\dot V_{O_2 }$ were significantly reduced in the lowland but not the high altitude lizards. The effects of simulated altitude conditions on the lowland but not the mountaine animals indicate adaptations to altitude in these sceloporine lizards. We did not find any consistent relationship between organ/body weight ratios or hematocrit and our measures of$\dot V_{O_2 }$ endurance or the altitude at which the lizards were captured.