IAB Research Project Description
IPY: Collaboration Research: Extremes of Hibernation Physiology: Patterns of Expression, Regulation, and Limits
Trixie Lee, graduate student in the Department of Biology and Wildlife at the University of Alaska Fairbanks, releases arctic ground squirrels near the Institute of Arctic Biology Toolik Field Station, North Slope, Alaska. Credit: Oivinid Toien/IAB/UAF
The arctic environment is characterized by extremes in photoperiod and temperature, short growing seasons, prolonged winters and extensive permafrost. Mammals overwintering in the Arctic either remain active, changing range and foraging strategies, or they enter hibernation by withdrawing to thermal refugia and surviving on stored energy while hypometabolic and hypothermic.
Although widespread among mammalian species as an adaptation to seasonal periods of poor food availability, hibernation perhaps has evolved to its physiological limits in arctic species due to the severity of the Arctic seasonal environment. Indeed, the arctic ground squirrel is the exemplar of one component of the hibernation phenotype at its extreme, as it is capable of supercooling to -2.9°C (the lowest body temperature (Tb) adopted by any mammal and reducing metabolism to 2% of basal metabolic rate for up to many days at a time.
This project investigated the physiological limits to hibernation in the arctic ground squirrel, using a variety of field and lab-based studies. We tested a new method for evaluating lean mass use and conservation during fasting using variations in the nitrogen stable isotope ratio. These data revealed that squirrels use muscle tissue preferentially as fuel during hibernation, while conserving heart, liver, small intestine, and thermogenic (heat generating) tissue. We investigated the expression of key genes involved in severe metabolic reduction and characterized the metabolic profile of summer active and hibernating squirrels. Finally, we continued our ongoing investigation of free-living arctic ground squirrels at Toolik Field Station. These studies have been ongoing for decades, and recent analysis of these long data records have shown that the timing and duration of the season of hibernation are related to snow-cover, and that differences in the length and depth of hibernation relate to reproduction. Other studies are using these data to examine at biological rhythms; how they are suppressed during hibernation and re-set at the end of winter.
31 Aug 2007 – 31 Jul 2010
IAB Proposal #07-063
UAF Grant #G4307
IAB Project #139
302A Irving I
University of Alaska Fairbanks
Fairbanks, AK 99775-7000