Metabolic physiology of the north-western marsupial mole, Notoryctes caurinus (Marsupialia : Notoryctidae)

Abstract

We studied the thermal and metabolic physiology of a single specimen of the north-western marsupial mole, Notoryctes caurinus , an almost completely fossorial Australian marsupial, and compared it with the morphologically convergent Namib desert golden mole, Eremitalpa granti namibensis . This was the first study of any aspect of the physiology of this rare marsupial. Mean body mass of the marsupial mole was 34 g. Body temperature (Tb) was low and labile, ranging from 22.7 to 30.8°C over a range of ambient temperature (Ta) from 15 to 30°C. The highest Tb of 30.8°C was significantly lower than expected for a marsupial of this body mass. Metabolic rate varied with Ta in an attenuated fashion for an endotherm, because of the labile Tb. Basal metabolic rate (BMR) was 0.63 mL O2 g–1 h–1, at a Ta of 30°C. This was lower than expected for a 34-g marsupial, but was not different from expected for a marsupial when corrected to a Tb of 35°C (0.94 mL O2 g–1 h–1). Evaporative water loss increased from 0.8 mg g–1 h–1 at 15°C to 3.7 at 30°C. Wet thermal conductance was 0.2 mL O2 g–1 h–1 °C–1 at 15°C and 0.6 at 25°C; these values were higher than expected for a marsupial. The net metabolic cost of transport (NCOT) for running (0.0022 mL O2 g–1 m–1 at a mean velocity of 484 m h–1) was similar to expected values for walking and running mammals. The NCOT for sand-swimming (0.124 mL O2 g–1 m–1 at a mean velocity of 7.6 m h–1) was substantially higher, and at a much lower velocity than for running, but was similar to NCOT for sand-swimming by the Namib golden mole. We conclude that the marsupial mole differs in some aspects of thermal and metabolic physiology from other marsupials, most likely reflecting its almost completely fossorial existence.