The effects of caloric restriction on the body composition and hibernationof the golden-mantled ground squirrel (Spermophilus lateralis)

In preparation for hibernation, golden-mantled ground squirrels (Spermophil us lateralis) must deposit sufficient amounts of lipid during the summer to survive winter hibernation. We conducted an experiment from May 1998 to Fe bruary 1999 to examine the effects of caloric restriction on the body compo sition (lipid and fat-free mass) and hibernation of golden-mantled ground s quirrels. Ground squirrels were either provided with food ad lib. (controls ) or with only enough food to maintain a constant body mass throughout the experiment (calorically restricted). Changes in body composition were follo wed using total body electrical conductivity (TOBEC). Implanted data logger s that recorded body temperature were used to determine when ground squirre ls entered their first torpor bout and the lengths of torpor bouts. Body co mposition did not change in the calorically restricted ground squirrels bet ween May and September, while both lipid and fat-free mass increased in the controls. However, from September to February, calorically restricted grou nd squirrels lost only fat-free mass, not lipid mass, but controls lost bot h lipid and fat-free mass. Calorically restricted ground squirrels entered their first torpor bout about 4 wk after controls, but the torpor bout dura tion (or length) during hibernation did not differ between the two groups. These results show that ground squirrels maintain body composition during c aloric restriction, and the limited quantities of stored lipid have an effe ct on when hibernation begins but not on torpor bout length.