Factors influencing the prediction of metabolic rate in a reptile

Summary 1Measurements of the rate of oxygen consumption (V̇o2) in the field are usually impractical, so several studies of endotherms have utilized heart rate (fH) as a correlate of V̇o2 because of the tight relationship that often exists between the two variables. There have been several reports, however, where the relationship between fH and V̇o2 changes or disassociates under different physiological or psychological circumstances. This may be further confounded in ectothermic vertebrates, which experience relatively large fluctuations in body temperature (Tb).2The aim of the present study was to characterize in Rosenberg's Goanna (Varanus rosenbergi) the relationship that exists between Tb, fH and V̇o2 at rest and at different levels of exercise, during periods of heating and cooling, and following ingestion of a meal.3The combinations of Tb and fH were accurate at predicting V̇o2 of animals at different levels of exercise and recovery, and during the postprandial period.4Predictions of V̇o2 became less reliable during periods of relatively rapid heating when fH and blood flow increase for thermoregulatory purposes with no associated increase in V̇o2. To counter this, fH was excluded from the prediction equation when the rate of heating exceeded 20% of the predicted mass-dependent maximum attainable rate, and V̇o2 was predicted using Tb alone.5The resultant V̇o2 prediction equation was used to estimate V̇o2 of seven animals that were allowed to thermoregulate behaviourally, and the mean predicted V̇o2 (V̇o2pred) was not significantly different from the mean measured V̇o2 (V̇o2meas) for fasting or postprandial lizards.