Ventilation, Gas Exchange, and Aerobic Scope in a Small Monitor Lizard, Varanus gilleni

Standard rates of O₂ consumption (V̇o2) in the dark of Varanus gilleni (mean mass = 30 g) were measured at 25, 31, 34, and 37 C. At 37 C, the mean value (195 ml O₂ STPD kg⁻¹ h⁻¹) was 22% lower than that predicted by a regression equation for lizards as a group (Bennett and Dawson 1976). Despite appearing to be asleep, three-to fourfold elevations in standard V̇o2 were seen in lizards with lightweight, transparent respiratory masks. V̇o2 was also measured during treadmill exercise at speeds from 5 to 15 m min⁻¹ and during bouts of maximal exercise. Varanus gilleni has the highest factorial aerobic scope (27.5) of any lizard examined to date. The cost of transport in V. gilleni is relatively high and may relate to short limb length. Pulmonary ventilation and gas exchange (V̇e, V̇o2, V̇co2) were simultaneously measured at 25 C, during warming from 25 to 35 C, and again after several hours at 35 C. Air-convection requirements for CO₂ and O₂ were independent of temperature. The patterns of lung ventilation suggest that arterial PCO₂ and pH are constant with rising temperature, behavior that is common to that in large varanids and in contrast to that in other reptiles.