Metabolic Physiology of Euthermic and Torpid Honey Possums, Tarsipes-Rostratus

Euthermic honey possums have a higher body temperature (Tb), basal metabolic rate and wet thermal conductance than other marsupials of similar mass. Honey possums enter torpor when cold-stressed and deprived of food. The pattern of decline in body temperature and oxygen consumption during torpor generally resembles that of other heterothermic endotherms. The duration of torpor bouts in honey possums was about 10 h; torpor bouts longer than one day were not observed. The Tb declined during torpor to within 1-2�C of ambient temperature (Ta>5�C) and oxygen consumption rate declined dramatically. The minimal body temperature (Tb,min) measured for torpid honey possums was about 5�C, because Tb was regulated at about 5�C by honey possums torpid at Ta<5�C, by an elevation of oxygen consumption rate. Previous studies of small marsupials have delineated two basic patterns of torpor: (1) shallow (Tb,min>10-15�C) and short-term torpor cycles (e.g. in dasyurids); (2) deep (Tb,min<10�C) and multi-day torpor cycles (e.g. in burramyids). Honey possums appear to have a third pattern of deep (Tb,min=5�C) but short-term torpor. The ecological reasons for this pattern of deep torpor and the apparent absence of multi-day torpor in honey possums may be related to their nectarivorous diet and lack of extensive fat stores.