This project assesses the costs and consequences for small hibernating mammals overwintering in an arctic environment. It investigates patterns of body temperature change and the phenology of hibernation in a natural population of arctic ground squirrels in Northern Alaska and tests hypotheses about the effect of diet and burrow choice for individual survivorship and reproduction. This project will test the diet hypotheses, in collaboration with Dr. C. L. Frank, which revolves around the role of plant-derived essential fatty acids in constraining hibernation physiology. Laboratory-based experiments will be conducted that quantify the metabolic costs of hibernating under arctic temperature conditions and investigate the fundamental basis for what limits how long mammals can stay hypothermic and hypometabolic during hibernation. The fieldwork continues a long-term physiological monitoring program of this arctic mammal population.
The project will focus on the following specific goals: (1a) Using automated sensing, describe the timing of immergence into and emergence from hibernation, natural limits to supercooling during torpor, pattern and duration of periodic arousals, and how sex, reproductive, and age cohorts of arctic ground squirrels differ in hibernation patterns and phenology. (1b) Measure annual soil temperature profiles at each individual's hibernaculum. Pilot data show that minimum hibernacula temperatures vary from -7 to - 25 0C determine the sources of this variation (surface and soil physical and climatological features) and the extent of spatial (among-burrow) and temporal (among-year) variation. Manipulate physical factors such as vegetation and snow cover over burrows by altering snowdrift and determine the thermal consequences for the hibernaculum and its occupant. (2) Correlate variation in overwinter survivorship or change in body condition in surviving individuals with thermal features of their hibernacula. Because they expend more energy maintaining larger thermal gradients between body and soil, ground squirrels occupying colder burrows should suffer more mortality or lose more body stores during hibernation than do animals occupying warmer burrows. These experiments investigate the effect of the winter physical environment and its spatial and temporal variation on fat and lean loss and survivorship and, since spring fecundity is affected by overwinter body mass loss, reproductive fitness of a key arctic mammalian species. (3) Test the effect of dietary lipids and polyunsaturated level of adipose tissue on the pattern and depth of hibernation and overwinter survivorship of individuals. The concentration of essential fatty acids obtained from arctic plants during fattening in arctic ground squirrels will be determined from a biopsy of depot fat taken when data loggers are implanted, and dietary lipids will be manipulated in captive animals. (4) Results from sampling animals as they enter and emerge from hibernation in successive years will add to our long-term data set on the physiological ecology, chronology, endocrinology, and life-history characteristics of this arctic population of ground squirrels. Set in the context of the other long-term ecological and physiological research done at the Toolik Field Station, these experiments can integrate the role of a key mammalian herbivore into the systems approach of study of this arctic community. The following laboratory experiments quantify the energetic costs of hibernation in arctic conditions and investigate the nature of limits to how long a mammal can stay in hibernation. (5) Determine steady-state metabolic rate, metabolic fuel use, and sources of thermogenesis in arctic ground squirrels hibernating at ambient temperatures of -20 to +20 0C. (6) Measure maximum torpor bout length (TBL) of animals hibernating in conditions of -20 to +20 0C and monitored for body and brain temperature. Maximum TBL should inversely reflect the rate by which an unknown process(es) deviates from homeostatic levels during hibernation. Since body temperature and metabolic rate become uncoupled in arctic ground squirrels hibernating over this temperature range, we can investigate the nature of this process, which may represent a fundamental constraint to continued homeostasis during hypothermia and hypometabolism in mammals. ***
