Development of thermoregulation in the sugar glider Petaurus breviceps (Marsupialia : Petauridae)

Young, relatively undeveloped sugar gliders Petaurus breviceps have been ob served to be left alone in the nest while the mother forages and may be sub ject to considerable thermal or energetic stress. As no information is avai lable on the development of thermoregulation in this species, which begins reproduction in winter, we measured resting metabolic rate (RMR), body temp erature (T-b) and thermal conductance over a range of ambient temperatures (T-a) in 10 sugar gliders from c. 55 days of age until they had grown to ad ult size. Sugar gliders were unable to maintain a stable T-b over a T-a ran ge of 30-15 degreesC until the age of 95-100 days, although they raised RMR somewhat as T-a decreased. Further growth resulted in a steady decrease in mass-specific RMR, an increase in Tb and a substantial decrease in thermal conductance. Our study shows that young gliders below the age of 100 days rely largely on heat produced by adults to maintain a high T-b, but are wel l able to cope with regular falls in T-b of > 10 degreesC and a concomitant decrease of RMR. This thermal tolerance and reduction in energy expenditur e should allow the mother to forage and replenish her own body fuels while her offspring are left alone in the nest.