LIPID DEPOSITION AND USE BY BLACK-TAILED PRAIRIE DOGS, CYNOMYS-LUDOVICIANUS, IN THE NATURAL-ENVIRONMENT

Fatty acid synthase (FAS) activity was measured in black-tailed prairie dogs (Cynomys ludovicianus), nonhibernators or facultative hibernators, to compare their enzyme activity associated with fattening to that reported earlier (Turner et al. 1989) in Richardson's ground squirrels (Spermophilus richardsonii), obligate hibernators. In both species nearly all FAS activity was in white adipose tissue (WAT). Maximum FAS activity/mg of protein in WAT occurred after reproduction in both species and was about three times as great in ground squirrels as in prairie dogs. When rate of fat deposition was at its peak (June-August in ground squirrels, fall in prairie dogs), total FAS in WAT in ground squirrels was twice that in prairie dogs. Richardson's ground squirrels deposited approximately 9 g of lipid/wk during peak fattening (Turner et al. 1989) versus approximately 5 g of lipid/wk in prairie dogs. These observations support the hypothesis that obligate hibernators fatten more rapidly than nonhibernators. During 3 wk of cold in the winter of 1990-1991 (air temperature less than -20-degrees-C), prairie dogs lost 30% of body weight, nearly all of which was lean body mass. Lipid mass was depleted during the reproductive season, from March through June. As a result of this observation, the following year lipolytic activity in liver, WAT, and brown adipose tissue (BAT) as well as body and tissue masses was measured monthly in free-roaming prairie dogs. Liver and WAT were the principal sites of lipolytic activity. Although 1991-1992 was not as severe as the previous winter, use of lipid stores was similar. Fat deposits remained intact through fall and early winter, and lipolytic activity was low in all tissues. Reproductive activity began in February and March in males and females, respectively. Between january and March lipolytic activity in liver tripled in both sexes. During the same period lipolytic activity in WAT doubled in females and quadrupled in males. During the reproductive season males lost 85% and females lost 91% of lipid stores. Black-tailed prairie dogs foraged throughout the year but during severe cold remained underground and catabolized primarily lean body mass. Lipolytic activity and amount of lipid present supported the hypothesis that lipid reserves are conserved through winter and supply energy for reproduction.