Daily Torpor and Thermoregulation in the Small Dasyurid Marsupials Planigale-Gilesi and Ningaui-Yvonneae

Abstract

Torpor in endotherms has only been observed in small species, suggesting that body mass determines the occurrence of torpor. The present study investigates the influence of body mass on the occurrence of torpor and also the pattern of torpor (i.e. minimum body temperature, metabolic rate, and the duration of torpor). The two small dasyurid marsupials Planigale gilesi (8.3 g) and Ningaui yvonneae (11.6 g) entered torpor frequently when food was available; withdrawal of food increased the occurrence of torpor to almost 100%. Minimum body temperatures during torpor in both species were lower and the torpor duration was longer than for most larger dasyurid species studied so far. These findings suggest that the thermal stress on these very small species exerts a strong selective pressure to enhance daily torpor episodes for reduction of heat loss to the environment.