Abstract
A growing number of mammal species are recognized as heterothermic, capable of maintaining a high-core body temperature or entering a state of metabolic suppression known as torpor. Small mammals can achieve large energetic savings when torpid, but they are also subject to ecological costs. Studying torpor use in an ecological and physiological context can help elucidate relative costs and benefits of torpor to different groups within a population. We measured skin temperatures of 46 adult Rafinesque's big-eared bats (Corynorhinus rafinesquii) to evaluate thermoregulatory strategies of a heterothermic small mammal during the reproductive season. We compared daily average and minimum skin temperatures as well as the frequency, duration, and depth of torpor bouts of sex and reproductive classes of bats inhabiting day-roosts with different thermal characteristics. We evaluated roosts with microclimates colder (caves) and warmer (buildings) than ambient air temperatures, as well as roosts with intermediate conditions (trees and rock crevices). Using Akaike's information criterion (AIC), we found that different statistical models best predicted various characteristics of torpor bouts. While the type of day-roost best predicted the average number of torpor bouts that bats used each day, current weather variables best predicted daily average and minimum skin temperatures of bats, and reproductive condition best predicted average torpor bout depth and the average amount of time spent torpid each day by bats. Finding that different models best explain varying aspects of heterothermy illustrates the importance of torpor to both reproductive and nonreproductive small mammals and emphasizes the multifaceted nature of heterothermy and the need to collect data on numerous heterothermic response variables within an ecophysiological context.
Highlights
Heterothermic small mammals are notable for their ability to enter a state of metabolic suppression known as torpor (Geiser 2004; Storey et al 2010; Geiser and Brigham 2012)
Torpor is often recognized as hibernation, a winter survival strategy essential to many temperate zone species. It is becoming increasingly apparent, that torpor is used throughout the year for numerous physiological purposes, revising our understanding of the costs and benefits associated with torpor outside of hibernation (Geiser and Brigham 2012; Dzal and Brigham 2013)
Torpor is undeniably a powerful adaptation, an adaptation frequently used in response to internal stressors such as energetic demands, as well as environmental stressors such as weather (McLean and Speakman 1999; Willis et al 2006; Schmid and Speakman 2009; Dzal and Brigham 2013)
Summary
Heterothermic small mammals are notable for their ability to enter a state of metabolic suppression known as torpor (Geiser 2004; Storey et al 2010; Geiser and Brigham 2012). Torpor is often recognized as hibernation, a winter survival strategy essential to many temperate zone species. It is becoming increasingly apparent, that torpor is used throughout the year for numerous physiological purposes, revising our understanding of the costs and benefits associated with torpor outside of hibernation (Geiser and Brigham 2012; Dzal and Brigham 2013). Torpor use by reproductive females (Willis et al 2006; Dzal and Brigham 2013) is an emerging example of how we must revise our understanding of the costs and benefits of torpor.
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