Thermal, metabolic, hygric and ventilatory physiology of the sandhill dunnart (Sminthopsis psammophila; Marsupialia, Dasyuridae)

Abstract

We present here the first physiological data for the sandhill dunnart (Sminthopsis psammophila), the second largest (35–44 g) sminthopsine dasyurid marsupial, and report torpor for this species. Their thermoneutral body temperature (34.4 °C), thermolability below thermoneutrality (0.062 °C °C− 1), and mild hyperthermia above thermoneutrality (35.5 °C) are typical of small dunnarts, and dasyurids. Basal metabolic rate (0.80 mL O2 g− 1 h− 1) is as predicted from mass. Sandhill dunnarts generally conform to the Scholander–Irving model of endothermy, although metabolism increases less than expected and extrapolates to a higher than actual body temperature. Wet (0.22 mL O2 g− 1 h− 1 C− 1) and dry (2.8 J g− 1 h− 1 °C− 1) thermal conductances were as predicted. Thermoneutral evaporative water loss (1.6 mg g− 1 h− 1) was only 54% of expected, but this is not significantly different, and more likely reflects variability in the marsupial dataset than an adaptation. Relative water economy resembles that of other small marsupials, rodents and birds, with a point of relative economy of 18 °C. Respiratory ventilation closely matches metabolic rate, with minute volume increased at low ambient temperatures by increased breathing rate rather than tidal volume; oxygen extraction was constant at about 17%, except during hyperthermia above the thermoneutrality. Torpor conferred significant energetic and hygric benefits. We found no evidence of deviation from allometrically- and phylogenetically-based expectations despite the sandhill dunnart's arid habitat and large (for a dunnart) body mass.