Energy metabolism in potoroine marsupials

Fasting and fed metabolic rates were measured in three species of potoroine marsupials, the rufous rat-kangaroo (Aepyprymnus rufescens), the long-nosed potoroo (Potorous tridactylus) and the brush-tailed bettong (Bettongia penicillata). There were no significant differences among potoroine species in fasting metabolic rate. The lowest fasting heat production for each species was 11-20% less than the interspecific value of 295 kJ.kg-0.75.day-1 for basal metabolism of mature, non-reproductive eutherian homeotherms. The respiratory quotient of all species was reduced significantly as starvation proceeded, but only for B. penicillata was there a significant effect of starvation duration on fasting heat production. The night-time activity of P. tridactylus and B. penicillata doubled their daytime fasting heat production; the corresponding increase for A. rufescens was only 25%. The calorimetric measurement of fed animals showed no differences in digestible energy or metabolisable energy between species. Nevertheless, P. tridactylus and B. penicillata produced more heat per unit metabolic body mass. The maintenance energy requirements (kJ.kg-0.75.day-1) were 479, 494 and 345 for P. tridactylus, B. penicillata and A. rufescens, respectively. The net availability of metabolisable energy was about 0.70 in the three species. The combined heat production of fed female A. rufescens and their pouch young stayed relatively constant for the first two-thirds of pouch life, after which it rose sharply (20%) in response to the rapid growth of the young. Only during the last week of pouch life did the female enter negative energy balance. There was no indication that the metabolism of the female increased in response to the presence of a pouch young. The presence of pouch young did not alter the efficiency of utilisation of metabolisable energy. The daily energy requirement for maintenance was 0.83 MJ.day-1 or 0.36 MJ.kg-0.75.day-1.