Contrasting thermal strategies of montane Neotropical bats at high elevations

Abstract

In the Neotropics, captive vespertilionid bats substantially reduce their metabolic rate at low ambient temperatures, similar to their temperate counterparts, whereas the ability of phyllostomids to lower metabolic rate seems to be more limited, even in mountain species. Nevertheless, field data on the thermal behaviour of syntopic individuals from these two families is lacking. Consequently, we aimed to test whether torpor was more common and deeper in vesper bats compared to leaf-nosed bats by studying skin temperature (Tsk) variation in individuals experiencing the same environmental conditions at a mountain area. Bats experienced ambient temperatures below 15°C. Average Tsk was 10ºC in Myotis oxyotus gardneri (Vespertilionidae) during the day, while Sturnira burtonlimi (Phyllostomidae) regulated diurnal Tsk above 30ºC. Constant food availability may explain why diurnal Sturnira burtonlimii pay the high energetic cost required to remain normothermic and to defend a wide Ta-Tsk gap but further studies are needed to elucidate additional strategies that may be employed by these bats to reduce the energetic demands of normothermy. Our study shows that the contrasting thermal strategies and torpor use adopted by vespertilionid insectivores and phyllostomid frugivores in captive settings also occur in free-ranging conditions, thus providing a basis to develop further studies with predictions more accurately rooted in field data.

Body mass affects short‐term heterothermy in Neotropical bats

“…The lowest post‐exposure T b s were recorded from small insectivorous bats; however, the lowest pre‐exposure T b s were recorded from larger frugivorous bats. While the low post‐exposure T b in smaller bats is expected due to higher conductance (McNab, 1980), and torpor being commonly employed by small tropical insectivorous bats (Garin et al., 2018; Machado & Soriano, 2007; McNab, 1969; Soriano et al., 2002; Studier & Wilson, 1970), the low pre‐exposure T b of larger frugivorous bats was unexpected. Previous data regarding thermoregulation of Neotropical frugivorous bats are scant and considerably variable between studies and sometimes within the same species (McNab, 1969; Studier & Wilson, 1970).…”

“…When comparing free‐ranging bats from the same area, Garin et al. (2018) found that Myotis oxyotus defended T b nearly 20°C cooler than did S. burtonlimi, which only allowed a decrease in T b by 5–6°C. In other phyllostomids, a mere 6°C reduction in T b upon exposure to cool T a translates to an energy savings of up to 30% (Audet & Thomas, 1997).…”

“…And if so, what are the parameters that best outline the magnitude of heterothermic bouts? Recent work has shifted the paradigm for mammalian heterothermy from being an adaptation exclusively for temperate‐zone species to cope with cold temperatures to an understanding that heterothermy is widespread among phylogenetically diverse tropical and subtropical mammalian taxa (Cory Toussaint & McKechnie, 2012; Czenze & Dunbar, 2017; Dausmann, Glos, Ganzhorn, & Heldmaier, 2004; Garin, Chaverri, Jimenez, Castillo‐Salazar, & Aihartza, 2018; Geiser & Stawski, 2011; Hallam & Mzilikazi, 2011; Lovegrove, 2012; Ruf & Geiser, 2015; Ruf, Streicher, Stalder, Nadler, & Walzer, 2015; Turbill, Law, & Geiser, 2003); however, the majority of these studies were conducted on subtropical and tropical Australasian and African species. Likewise, the body of literature demonstrating the utility of heterothermy in warm‐climate bats is growing (Busse, Lutter, Heldmaier, Jastroch, & Meyer, 2014; Czenze & Dunbar, 2017; Garin et al., 2018; Machado & Soriano, 2007); however, nearly all available studies focus on insect‐eating species (but see; Audet & Thomas, 1997; Ayala‐Berdon, Vázquez‐Fuerte, Beamonte‐Barrientos, & Schondube, 2017; Kelm & Von Helversen, 2007).…”