Effect of torpor on the water economy of an arid-zone marsupial, the stripe-faced dunnart ('Sminthopsis macroura')

Abstract

Metabolic rate and evaporative water loss (EWL) were measured for a small, arid-zone marsupial, the stripe-faced dunnart ('Sminthopsis macroura'), when normothermic and torpid. Metabolic rate increased linearly with decreasing ambient temperature (Ta) for normothermic dunnarts, and calculated metabolic water production (MWP) ranged from 0.85±0.05 (Ta=30°C) to 3.13±0.22 mg H2O g⁻¹ h⁻¹ (Ta=11°C). Torpor at Ta=11 and 16°C reduced MWP to 24–36% of normothermic values. EWL increased with decreasing Ta, and ranged from 1.81±0.37 (Ta=30°C) to 5.26±0.86 mg H2O g–1 h⁻¹ (Ta=11°C). Torpor significantly reduced absolute EWL to 23.5–42.3% of normothermic values, resulting in absolute water savings of 50–55 mg H2O h⁻¹. The relative water economy (EWL/MWP) of the dunnarts was unfavourable, remaining >1 at all Ta investigated, and did not improve with torpor. Thus torpor in stripe-faced dunnarts results in absolute, but not relative, water savings.