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

Abstract

Oxygen consumption ([(V)\dot]O2 )(\dot V_{O_2 } ) was measured at rest and during spontaneous activity at body temperatures of 25 and 35C in 14 fasting Savanna monitor lizards,Varanus exanthematicus ranging in weight from 172 to 7500 g. The allometric relationship between metabolic rate at 25C and body weight (W) is given by: [(V)\dot]O2 \dot V_{O_2 } (ml O2 STPDg–1hr–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 [(V)\dot]O2 \dot V_{O_2 } between 2400 and 0800 h (Fig. 1). Spontaneous activity and [(V)\dot]O2 \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 ([(V)\dot]/[(V)\dot]O2 )(\dot V/\dot V_{O_2 } ) and perfusion ([(Q)\dot]/[(V)\dot]O2 )(\dot Q/\dot V_{O_2 } ) requirements.