Metabolic, hygric and ventilatory physiology of a hypermetabolic marsupial, the honey possum (Tarsipes rostratus)

Abstract

The honey possum is the only non-volant mammal to feed exclusively on a diet of nectar and pollen. Like other mammalian and avian nectarivores, previous studies indicated that the honey possum's basal metabolic rate was higher than predicted for a marsupial of equivalent body mass. However, these early measurements have been questioned. We re-examined the basal metabolic rate (2.52 ± 0.222 ml O 2 g -1 h -1 ) of the honey possum and confirm that it is indeed higher (162%) than predicted for other marsupials both before and after accounting for phylogenetic history. This, together with its small body mass (5.4 ± 0.14 g; 1.3 % of that predicted by phylogeny) may be attributed to its nectarivorous diet and mesic distribution. Its high basal metabolic rate is associated with a high standard body temperature (36.6 ± 0.48 °C) and oxygen extraction (19.4%), but interestingly the honey possum has a high point of relative water economy (17.0°C) and its standard evaporative water loss (4.33± 0.394 mg H 2 O g -1 h -1 ) is not elevated above that of other marsupials, despite its mesic habitat and high dietary water intake.

The physiology of the honey possum, Tarsipes rostratus, a small marsupial with a suite of highly specialised characters: a review

“…Part of the reason for these unusual data may be that the seven animals in Cooper and Cruz-Neto's (2009) study, although listed as "adult honey possums" only weighed an average of 5.4 g. Male honey possums are not sexually mature until they reach 7-7.5 g, and typically weigh 8-12 g, with females being heavier at 10-14 g Russell and Renfree 1989;Bradshaw et al 2000). The individuals in Cooper and Cruz-Neto's (2009) study were thus juveniles and their mass-speciWc rate of oxygen consumption in the thermoneutral zone could reasonably be expected to be higher than that of fully grown adults.…”

“…This high value has been questioned (McNab 2005), given that marsupials traditionally have been found to have a BMR some 30% lower than that of similar-sized eutherian mammals (Dawson and Hulbert 1969;Dawson and Hulbert 1970). The question was re-examined by Cooper and Cruz-Neto (2009) who also reported a lower, but still elevated BMR of 2.52 § 0.22 mL O 2 g ¡1 h ¡1 (=6.56 kJ day ¡1 or 329 kJ kg ¡0.75 day ¡1 ). This Wgure is 162% of that predicted allometrically from BMR values of other marsupial species and 118% of that predicted for an eutherian mammal of the same mass (McNab 2008).…”

Ecological consequences of temperature regulation: Why might the mountain pygmy possumBurramys parvusneed to hibernate near underground streams?

“…16 Many small mammals, even tropical and mesic species, have a favorable relative water economy (i.e., they make more metabolic water than they lose by evaporation) when euthermic at moderate to low ambient temperatures. [23][24][25][26] However during torpor, their metabolic rate (and therefore metabolic water production) decreases proportionally more than their evaporative water loss, and so the relative water economy becomes more unfavorable, and water balance is typically negative. 16,[27][28][29][30] Water loss equivalent to about 5% body mass appears to be a critical limit requiring arousal from torpor, 31 and so it is likely that hibernating mammals reaching this limit must arouse to drink.…”