THE INFLUENCE OF DIETARY FATTY-ACIDS ON HIBERNATION BY GOLDEN-MANTLED GROUND-SQUIRRELS (SPERMOPHILUS-LATERALIS)

Golden-mantled ground squirrels (Spermophilus lateralis) are herbivores that hibernate during winter. A physiological limitation on hibernation may be the melting point of stored fat, since lipids must be fluid to be metabolizable and the body temperatures maintained during torpor are often 25-degrees-C below the melting point of mammalian fats. Previous analyses of depot fats from hibernating squirrel species revealed that they contained large amounts of polyunsaturated fatty acids, which greatly reduced the melting points of these lipids. Because polyunsaturated fatty acids cannot be synthesized by mammals but are commonly produced by plants, it was predicted that high dietary levels of polyunsaturates were required for proper hibernation. This hypothesis was tested in laboratory feeding and hibernation experiments involving captive S. lateralis maintained on diets of different polyunsaturate contents. Squirrels fed a high polyunsaturate diet (1) were more likely to hibernate, (2) had lower mortality during hibernation, and (3) defended lower body temperatures during torpor than those squirrels fed diets with lower concentrations of polyunsaturates. These results demonstrate that the ability of ground squirrels to hibernate depends on dietary polyunsaturate content.