Ontogeny and allometry of metabolic rate and ventilation in the marsupial: Matching supply and demand from ectothermy to endothermy

The ‘supply’ of substrates should match ‘demand’ for energy utilization and not limit it. Integration of supply to demand would be expected to occur during ontogeny. As a result of a short gestation and protracted lactation most development in marsupials occurs ex utero in a thermally stable pouch, hence there is an early reliance on atmospheric oxygen. This paper explores through allometry the matching of ventilation (supply) and rate of oxygen consumption (demand) in the tammar wallaby from birth to adulthood, covering four orders of magnitude and the transition from ectothermy to endothermy. The allometric exponent for the scaling equation for the rate of oxygen consumption in the ectothermic and endothermic phases of development was 0.78, the difference in intercept between the two equations being approximately 2.5-fold. A similar exponent and factorial increase in intercept was found for ventilation. Hence, convective requirement is mass independent throughout development, from ectothermy to endothermy, being similar to previously published values for the class Mammalia. Altogether, these results support the notion that, at rest, supply by ventilation is matched to demand for oxygen during postnatal development in the marsupial.