Winter torpor expression varies in four bat species with differential susceptibility to white-nose syndrome

Abstract

Studies examining the overwintering behaviors of North American hibernating bats are limited to a handful of species. We deployed temperature-sensitive transmitters on four species of bat that exhibit differences in their susceptibility to white nose syndrome (WNS; Myotis grisescens, M. leibii, M. sodalis, and Perimyotis subflavus) to determine if these differences are correlated with behavior exhibited during hibernation (i.e., torpor expression and arousal frequency). Mean torpor skin temperature (Tsk) and torpor bout duration varied significantly among species (P ≤ 0.024), but arousal Tsk and duration did not (P ≥ 0.057). One of the species with low susceptibility to WNS, M. leibii, had significantly shorter torpor bout durations (37.67 ± 26.89 h) than M. sodalis (260.67 ± 41.33 h), the species with medium susceptibility to WNS. Myotis leibii also had significantly higher torpor Tsk (18.57 °C ± 0.20) than M. grisescens (13.33 °C ± 0.60), a second species with low WNS susceptibility. The high susceptibility species, Perimyotis subflavus, exhibited low torpor Tsk (14.42 °C ± 0.36) but short torpor bouts (72.36 ± 32.16 h). We demonstrate that the four cavernicolous species examined exhibit a wide range in torpid skin temperature and torpor bout duration. Information from this study may improve WNS management in multispecies hibernacula or individual species management by providing insight into how some species may differ in their techniques for overwinter survival.

Roost thermal stability influences winter torpor patterns in a threatened bat species

“…Tri-colored bats at SRS exhibited winter torpor patterns nearer the short-term torpor end of the torpor continuum with characteristics reminiscent of daily heterotherms and as a result, might be less susceptible to WNS than populations nearer the hibernation end. Although tricolored bat's Tsk often fell within the optimal temperature growth range of Pd (Verant et al 2012), similar to susceptible subterranean populations (Sirajuddin 2018;Jackson et al 2022), PdBD was responsive to Ta and torpid Tsk often rose above 20°C due to passive fluctuations.…”

Emergence activity at hibernacula differs among four bat species affected by white‐nose syndrome

“…Additionally, data from these sites post‐WNS establishment indicate that these larger‐bodied species have longer torpor bouts than the smaller species examined, with eastern small‐footed and tricolored bats arousing more frequently than Indiana bats (Jackson et al, 2022). Evidence suggests that gray bats may benefit from their inherent behaviors of long torpor bouts in cold temperatures at the low end of the thermal growth optimum for Pd (~12.5–15.8°C; Jackson et al, 2022; Verant et al, 2012). In comparison to gray bats, Indiana bats may be suffering the effects of WNS due to their hibernation behavior.…”

“…In comparison to gray bats, Indiana bats may be suffering the effects of WNS due to their hibernation behavior. Although Indiana bats have long torpor bouts and seem to arouse infrequently, data from this region indicate that the species hibernates at much warmer body temperatures, just outside the upper thermal optimum of Pd growth (Jackson et al, 2022; Verant et al, 2012). The medium–high susceptibility exhibited by Indiana bats may be an artifact of long periods spent in torpor in prime Pd growing conditions, increasing their chances for Pd infection (Langwig et al, 2016).…”

“…The large clusters formed by gray bats and Indiana bats during hibernation reduce energy expenditure and total evaporative water loss, which could limit the need for numerous arousals (Barbour & Davis, 1969;Boratynski et al, 2015;Boyles et al, 2008Boyles et al, , 2020Tuttle, 1979). Additionally, data from these sites post-WNS establishment indicate that these larger-bodied species have longer torpor bouts than the smaller species examined, with eastern small-footed and tricolored bats arousing more frequently than Indiana bats (Jackson et al, 2022). Evidence suggests that gray bats may benefit from their inherent behaviors of long torpor bouts in cold temperatures at the low end of the thermal growth optimum for Pd (~12.5-15.8°C; Jackson et al, 2022;Verant et al, 2012).…”

“…Multiple mechanisms influencing susceptibility to WNS are being explored, mainly in relation to hibernation ecology, torpor physiology, skin microbiota, and immune function (Hoyt et al, 2021). Periodic winter activity, one aspect of hibernation ecology, has been hypothesized to minimize susceptibility to Pd invasion and WNS infection (Bernard et al, 2017; Jackson et al, 2022; Moosman et al, 2015; Reynolds et al, 2017), as repeated arousals throughout hibernation may allow bats to groom more frequently, likely removing fungal conidia in the process and reducing Pd loads (Brownlee‐Bouboulis & Reeder, 2015). This episodic activity also raises body temperature, activating the immune system, and possibly slowing Pd growth, potentially resulting in milder infections (Prendergast et al, 2002; Dobony et al, 2011; Rowley & Alford, 2013; Verant et al, 2014).…”