Torpor and basking in a small arid zone marsupial

Abstract

The high energetic cost associated with endothermic rewarming from torpor is widely seen as a major disadvantage of torpor. We tested the hypothesis that small arid zone marsupials, which have limited access to energy in the form of food but ample access to solar radiation, employ basking to facilitate arousal from torpor and reduce the costs of rewarming. We investigated torpor patterns and basking behaviour in free-ranging fat-tailed dunnarts Sminthopsis crassicaudata (10 g) in autumn and winter using small, internal temperature-sensitive transmitters. Torpid animals emerged from their resting sites in cracking soil at approximately 1000 h with body temperatures as low as 14.6 degrees C and positioned themselves in the sun throughout the rewarming process. On average, torpor duration in autumn was shorter, and basking was less pronounced in autumn than in winter. These are the first observations of basking during rewarming in S. crassicaudata and only the second direct evidence of basking in a torpid mammal for the reduction of energetic costs during arousal from torpor and normothermia. Our findings suggest that although overlooked in the past, basking may be widely distributed amongst heterothermic mammals. Therefore, the energetic benefits from torpor use in wild animals may currently be underestimated.

Torpor in Dark Times: Patterns of Heterothermy Are Associated with the Lunar Cycle in a Nocturnal Bird

“…3 predation risk or variable environmental temperatures) might also be important determinants of heterothermy in endotherms (Bieber and Ruf 2009;Mzilikazi et al 2002;Stawski and Geiser 2010;Warnecke et al 2008). Efforts have been made to generalize all factors affecting the expression of T b , whether well studied or not, into an adaptive framework (Angilletta et al 2010;Humphries et al 2003).…”

Basking hamsters reduce resting metabolism, body temperature and energy costs during rewarming from torpor

“…However, basking has been observed in wild dasyurid marsupials not only during rest in the afternoon but also in the morning when animals are rewarming from torpor and therefore must remain concealed from diurnal predators (Geiser et al, 2002;Warnecke et al, 2008;Rojas et al, 2012), as would be the case for white P. sungorus on or near snow. Important in this regard is that in the past, differences in fur colour among dasyurid populations were considered to be of little importance from energetic, thermal and camouflage points of view because animals were considered to be nocturnal.…”

“…It appears that during thermal and energetic challenges, a metabolic feedback affects the organisation of the circadian rhythm and induces diurnality in small nocturnal rodents (van der Vinne et al, 2014). For Australian carnivorous dasyurid marsupials, considered nocturnal in the past, radio-telemetry has shown that some are in fact entirely or to a large extent diurnal in winter (Warnecke et al, 2008;Körtner et al, 2010). We predict that such studies on P. sungorus in the wild will reveal not only that the species is partially diurnal but also that it uses basking near or on snow for energy conservation.…”

“…However, recent data show that the high energetic costs required for rewarming from torpor can be largely avoided by behavioural thermoregulation and specifically basking in the sun. Basking behaviour in the morning has been observed in several torpid desert or savanna mammals with T b as low as 15°C (Geiser et al, 2002(Geiser et al, , 2004Warnecke et al, 2008;Thompson et al, 2015). This is despite the fact that many of these species are widely considered to be entirely nocturnal and risk predation during the day, especially when movement is slowed (Rojas et al, 2012).…”

Effects of Solar Radiation on Animal Thermoregulation

“…By decreasing T B and metabolic rate, small animals can substantially reduce energy expenditure. Though it requires energy to arouse from torpor, some mammals can choose sites exposed to solar radiation during the day and are able to bask in sunlight, using the passive absorption of radiant heat to rewarm their body and profit from the energy saved while torpid (Warnecke et al, 2008).…”