Abstract
White-nose syndrome (WNS) is a new disease of bats that has devastated populations in eastern North America. Infection with the fungus, Geomyces destructans, is thought to increase the time bats spend out of torpor during hibernation, leading to starvation. Little is known about hibernation in healthy, free-ranging bats and more data are needed to help predict consequences of WNS. Trade-offs presumably exist between the energetic benefits and physiological/ecological costs of torpor, leading to the prediction that the relative importance of spring energy reserves should affect an individual's use of torpor and depletion of energy reserves during winter. Myotis lucifugus mate during fall and winter but females do not become pregnant until after spring emergence. Thus, female reproductive success depends on spring fat reserves while male reproductive success does not. Consequently, females should be “thrifty” in their use of fat compared to males. We measured body condition index (BCI; mass/forearm length) of 432 M. lucifugus in Manitoba, Canada during the winter of 2009/2010. Bats were captured during the fall mating period (n = 200), early hibernation (n = 125), and late hibernation (n = 128). Adult females entered hibernation with greater fat reserves and consumed those reserves more slowly than adult males and young of the year. Consequently, adult females may be more likely than males or young of the year to survive the disruption of energy balance associated with WNS, although surviving females may not have sufficient reserves to support reproduction.
Highlights
Organisms must balance energy intake against expenditure in order to survive, and available energy must be partitioned between maintenance, somatic growth and reproduction
To test Humphries et al.’s (2003) prediction that the need for spring fat reserves should influence energy expenditure during hibernation we examined the effect of age/sex class on the use of energy reserves in an uninfected population of the species which appears most susceptible to White-nose Syndrome (WNS), the little brown bat (Myotis lucifugus)
We captured a total of 432 little brown bats (72 adult females, 137 adult males, 100 YOY females and 123 YOY males)
Summary
Organisms must balance energy intake against expenditure in order to survive, and available energy must be partitioned between maintenance, somatic growth and reproduction. White-nose Syndrome (WNS) is a new disease of bats which appears to cause just such an increase in energy expenditure leading to perhaps the most rapid wildlife population declines ever recorded [4,5]. The direct cause of mortality is poorly understood, affected bats are emaciated and have presumably used their hibernation energy stores too rapidly [6]. In addition to understanding the proximate causes of mortality, there is a need to generate hypotheses about how WNS may affect populations on a longer timescale. This requires the study of reference populations that have not yet been impacted by the disease [5,11]
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