Aerobic metabolism of the lizardVaranus exanthematicus: Effects of activity, temperature, and size

Summary

Oxygen consumption$(\dot V_{O_2 } )$ was measured at rest and during spontaneous activity at body temperatures of 25 and 35°C in 14 fasting Savanna monitor lizards,Varanus exanthematicus ranging in weight from 172 to 7500 g. The allometric relationship between metabolic rate at 25°C and body weight (W) is given by:$\dot V_{O_2 }$ (ml O₂ STPD·g⁻¹·hr⁻¹)=0.88W ^−0.43 (Fig. 2). Although statistical comparisons are equivocal, this intraspecific size dependence exceeds that reported for interspecific comparisons among reptiles and other vertebrate groups (Fig 3). A reproducible diurnal pattern of activity was observed in undisturbed animals with minimum values of$\dot V_{O_2 }$ between 2400 and 0800 h (Fig. 1). Spontaneous activity and$\dot V_{O_2 }$ generally reached peak values between 1200 and 2000 hrs. The average ratio of active aerobic metabolic rate (AMR) to minimum (standard) aerobic metabolic rate (SMR) was 8.2. This voluntary AMR/SMR inVaranus exceeds the AMR/SMR for most reptiles stimulated to exhaustion. The high aerobic capacity is consistent with other evidence for efficient exchange and transport of respiratory gases inV. exanthematicus; e.g., low or absent intracardiac shunt flow resulting in high arterial saturation and low ventilation$(\dot V/\dot V_{O_2 } )$ and perfusion$(\dot Q/\dot V_{O_2 } )$ requirements.