Heterothermy in pouched mammals - a review

Abstract

Hibernation and daily torpor (i.e. temporal heterothermy) have been reported in many marsupial species of diverse families and are known to occur in ~15% of all marsupials, which is a greater proportion than the percentage of heterothermic placentals. Therefore, we aimed to gather data on heterothermy, including minimal body temperature, torpor metabolic rate and torpor bout duration for marsupials, and relate these physiological variables to phylogeny and other physiological traits. Data from published studies on 41 marsupial species were available for the present analysis. Heterothermic marsupials ranged from small species such as planigales weighing 7 g to larger species such as quolls weighing up to 1000 g. We used the marsupial phylogeny to estimate various heterothermic traits where the current dataset was incomplete. The torpor metabolic rate in relation to basal metabolic rate (%) ranged from 5.2 to 62.8% in daily heterotherms and from 2.1 to 5.2% in marsupial hibernators, and was significantly correlated with the minimum body temperature in daily heterotherms (R² = 0.77, P < 0.001), but not in hibernators (R² = 0.10, P > 0.05). The mean torpor bout duration ranged from 2 to 15 h in daily heterotherms and from 85 to 342 h in hibernators, and decreased significantly with increasing minimum body temperature in daily heterotherms (R² = 0.31, P < 0.001), but was not significant in hibernators. Our results show that phylogeny has a significant influence on nearly all analysed individual traits and relationships between traits in daily heterotherms (n = 35), but not in hibernators (n = 6). However, allometric analyses show that many of the physiological parameters scale differently between hibernators and daily heterotherms.