The effect of activity on oxygen consumption, oxygen debt, and heart rate in the lizards Varanus gouldii and sauromalus hispidus

Abstract

Oxygen consumption and heart rate were measured during rest and activity in the lizards Varanus gouldii and Sauromalus hispidus . Oxygen debt was calculated from postactive oxygen consumption. Standard metabolic rates of the two animals are similar but Varanus consumes much more oxygen during activity than does Sauromalus (Fig. 1–3). The latter has a constant active metabolic rate above 30 ° C and accumulates a large oxygen debt, which is repayed slowly (Fig. 4). Varanus recovers rapidly from activity (Fig. 5), presumably because of the smaller lactacid debt incurred. Heart rate increment in Sauromalus is high (Fig. 8). This variable cannot be responsible for the limitation of active oxygen consumption; calculations of oxygen pulse suggest that an inability to increase A-V difference and/or stroke volume are implicated (Fig. 9). Varanus have evolved mechanisms to sustain high levels of oxygen consumption superior to those of other reptiles investigated. The role of anaerobiosis in the biology of both animals is discussed.