Cool echidnas survive the fire

Abstract

Fires have occurred throughout history, including those associated with the meteoroid impact at the Cretaceous-Palaeogene (K-Pg) boundary that eliminated many vertebrate species. To evaluate the recent hypothesis that the survival of the K-Pg fires by ancestral mammals was dependent on their ability to use energy-conserving torpor, we studied body temperature fluctuations and activity of an egg-laying mammal, the echidna (Tachyglossus aculeatus), often considered to be a 'living fossil', before, during and after a prescribed burn. All but one study animal survived the fire in the prescribed burn area and echidnas remained inactive during the day(s) following the fire and substantially reduced body temperature during bouts of torpor. For weeks after the fire, all individuals remained in their original territories and compensated for changes in their habitat with a decrease in mean body temperature and activity. Our data suggest that heterothermy enables mammals to outlast the conditions during and after a fire by reducing energy expenditure, permitting periods of extended inactivity. Therefore, torpor facilitates survival in a fire-scorched landscape and consequently may have been of functional significance for mammalian survival at the K-Pg boundary.

A new cue for torpor induction: charcoal, ash and smoke

“…Importantly, yellow-footed antechinus employed more torpor in this denuded landscape than in a laboratory study (Geiser, 1988) and also in free-ranging individuals (Rojas et al, 2014). Similar field observations with an increase in torpor use were also made for brown antechinus (Antechinus stuartii) and echidnas (Tachyglossus aculeatus) after management burns (Nowack et al, 2016a;Stawski et al, 2016). We therefore hypothesised that yellow-footed antechinus will increase torpor use in response to a decrease in food availability, but that smoke and a charcoal/ash substrate will further enhance torpor expression.…”

“…In contrast, for most terrestrial animals, food and water resources will be reduced once a fire has passed through an area (VanTassel et al, 2015;Coleman and Rieske, 2006) and ground cover and refuges will be scant or completely obliterated (Matthews et al, 2016;Stawski et al, 2016). Consequently, in terrestrial mammals, torpor has been shown to be an important energy-saving mechanism that can increase the chances of post-fire survival (Matthews et al, 2016;Nowack et al, 2016a;Stawski et al, 2016). While energy savings by using torpor can compensate for food shortage, they can potentially also reduce foraging requirements and other above-ground activities.…”

“…Previous studies on the response of free-ranging terrestrial mammals to fire have suggested that food reduction is likely to be an important, if not the primary cause of the increase in torpor use (Matthews et al, 2016;Nowack et al, 2016a;Stawski et al, 2016). A decrease in food abundance is indeed a well-known trigger for torpor induction in many heterothermic species, and other environmental cues, such as low ambient temperature (T a ) and a change in photoperiod, are often precursors to a reduction in food availability (Ruf et al, 1991;Song and Geiser, 1997;Stawski and Geiser, 2010;Levy et al, 2012;Williams et al, 2014;Vuarin et al, 2015).…”

“…The physiological and behavioural responses of individual mammals to fire have attracted some recent scientific attention (Scesny, 2006;Dickinson et al, 2010;Doherty et al, 2015;Perry and McDaniel, 2015;Doty et al, 2016;Matthews et al, 2016;Nowack et al, 2016a;Stawski et al, 2016). For example, volant bats employed less torpor, characterised by reduced metabolic rate and body temperature (T b ), shortly after a wildfire in comparison to 2 years later (Doty et al, 2016).…”

Daily energy expenditure in the face of predation: hedgehog energetics in rural landscapes

“…Another possibility is that hedgehogs compensated for the loss of food intake in the face of predation by decreasing their energy use in some way. Studies of predation risk after wildfires in echidnas and antechinuses have found that individuals compensated for loss of foraging opportunity by increasing torpor use (Nowack et al, 2016;Stawski et al, 2015). It could be that hedgehogs lower their body temperature in order to conserve energy when food intake is reduced owing to predation risk.…”