Water flux and field metabolic rate (FMR) were measured by the doubly labelled water (DLW) method in free-living male and female rufous rat-kangaroos Aepyprymnus rufescens near Drake in northern New South Wales. The mean FMR of 499 kJ kg-1 day-1 was similar in winter and summer even though the difference in mean minimum temperatures between the two seasons was 20-degrees-C. Furthermore, we did not find any differences in FMR between males and females even though several females carried large pouch young or had young-at-foot. A poor understanding of the diet and the behavioural ecology of A. rufescens makes ft difficult to explain the similarities between sexes and seasons.
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.
Field metabolic rates (FMRs) and water-flux rates of free-living male and female long-nosed potoroos (Potorous tridactylus) were measured in two seasons near Warrnambool in southern Victoria, Australia, using the doubly labelled water technique. Potoroos, which weighed about 835 g, expended 30% more energy (590 kJ day-1) in early spring than they did in midsummer (463 kJ day-1 ), despite mean minimum temperatures in the two seasons differing by only 4C. We did not find any difference in the FMRs of males and females even though all females carried pouch young or had young at foot. The mean water flux rates followed a similar seasonal trend to that of FMR with the summer mean influx rate (131 mL day-1 ) being 30% lower than that in spring (174 mL day-1 ). This difference in water-turnover rate may reflect changes in the seasonal water status of the environment. Hypogeous fungi constitute a major part of the diet of potoroos and the role played by this food source in supplying amino acids is discussed.
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