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Thermoregulatory changes anticipate hibernation onset by 45 days: data from free-living arctic ground squirrels

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Abstract

Hibernation is a strategy of reducing energy expenditure, body temperature (T b) and activity used by endotherms to escape unpredictable or seasonally reduced food availability. Despite extensive research on thermoregulatory adjustments during hibernation, less is known about transitions in thermoregulatory state, particularly under natural conditions. Laboratory studies on hibernating ground squirrels have demonstrated that thermoregulatory adjustments may occur over short intervals when animals undergo several brief, preliminary torpor bouts prior to entering multiday torpor. These short torpor bouts have been suggested to reflect a resetting of hypothalamic regions that control T b or to precondition animals before they undergo deep, multiday torpor. Here, we examined continuous records of T b in 240 arctic ground squirrels (Urocitellus parryii) prior to hibernation in the wild and in captivity. In free-living squirrels, T b began to decline 45 days prior to hibernation, and average T b had decreased 4.28 °C at the onset of torpor. Further, we found that 75 % of free-living squirrels and 35 % of captive squirrels entered bouts of multiday torpor with a single T b decline and without previously showing short preliminary bouts. This study provides evidence that adjustments in the thermoregulatory component of hibernation begin far earlier than previously demonstrated. The gradual reduction in T b is likely a component of the suite of metabolic and behavioral adjustments, controlled by an endogenous, circannual rhythm, that vary seasonally in hibernating ground squirrels.

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Acknowledgments

We would like to thank all who have worked with us on the arctic ground squirrel project over the past 16 years. Funding for this study was provided by the National Science Foundation to CLB and BMB (EF 07-32763/07-32755), the US Army Medical Research and Materiel Command Grant to BMB (05178001) and a National Science and Engineering Research Council post-doctoral fellowship to MJS.

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Authors and Affiliations

  1. Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AK, 99775, USA

    Michael J. Sheriff & Brian M. Barnes

  2. Department of Biological Sciences, University of Alberta, Edmonton, AB, T6G 2R3, Canada

    Cory T. Williams

  3. Burke Museum and Department of Biology, University of Washington, Seattle, WA, 98195, USA

    G. J. Kenagy

  4. Department of Biological Sciences, University of Alaska Anchorage, 3101 Science Circle, Anchorage, AK, 99508, USA

    C. Loren Buck

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  1. Michael J. Sheriff
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  2. Cory T. Williams
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  3. G. J. Kenagy
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  4. C. Loren Buck
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  5. Brian M. Barnes
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Correspondence to Michael J. Sheriff.

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Communicated by H. V. Carey.

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Sheriff, M.J., Williams, C.T., Kenagy, G.J. et al. Thermoregulatory changes anticipate hibernation onset by 45 days: data from free-living arctic ground squirrels. J Comp Physiol B 182, 841–847 (2012). https://doi.org/10.1007/s00360-012-0661-z

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  • DOI: https://doi.org/10.1007/s00360-012-0661-z

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