| Hibernators fed diets high in the polyunsaturated fatty acid (PUFA) linoleic acid have reduced energy demand during hibernation relative to those fed diets high in saturated fats, and may preferentially feed on diets high in linoleic acid during prehibernation fattening. In 1991-1994, I followed body composition dynamics of Townsend's ground squirrels (Spermophilus townsendii), and essential fatty acids (EFAs) in their plant foods and adipose tissue, on the Snake River Birds of Prey National Conservation Area in southwestern Idaho, to test for differences in fattening and EFA availability among years and habitats. Adult ground squirrels were smaller, yet fatter at hibernation in a drought year and in habitats with low apparent food availability. Mass and body composition at emergence from hibernation did not differ between years. I developed a model to demonstrate that energy expenditure in hibernation varied among years and habitats, accounting for apparent differences in mass loss overwinter. Diets of S. townsendii were low in fat, and low in linoleic acid. Diets and adipose tissues of ground squirrels varied in EFA content according to the availability of green vegetation in different habitats and among years. In contrast to other hibernators, S. townsendii, and perhaps other more strictly herbivorous hibernators, do not fatten on diets high in linoleic acid, and do not have a shift in EFA content of adipose tissue between mid- and late-active season.; Experiments with S. townsendii, testing effects of varying amounts of linoleic acid on hibernation, demonstrated that ground squirrels fed a low-PUFA diet experienced greater mortality during hibernation than those fed a high-PUFA diet. Survivors on the low-PUFA diet did not terminate hibernation spontaneously, and their torpor bouts were longer than those of ground squirrels fed the high-PUFA diet.; Experiments with the long-tailed pocket mouse, Chaetodipus formosus, testing effects of varying levels of linoleic acid on their ability to use daily torpor to maintain mass with decreasing temperature and food availability, demonstrated that pocket mice fed low-PUFA diets lost mass at the highest temperature, died at the lowest temperature, and tended to have shorter torpor bouts than mice on the high-PUFA diet. Linoleic acid appears to be important for pocket mice to be able to use torpor in their natural environment. |
