FASTING BIOCHEMISTRY OF REPRESENTATIVE SPONTANEOUS AND FACULTATIVE HIBERNATORS - THE WHITE-TAILED PRAIRIE DOG AND THE BLACK-TAILED PRAIRIE DOG

The white-tailed prairie dog is a spontaneous hibernator that enters a rt anorexic state followed by torpor in early fall. The black-tailed p rairie dog is a facultative hibernator that enters torpor only when de prived of food and water in the winter. The physiological state of hib ernation is similar to a Phase II euthermic fast characterized by elev ated fat catabolism, increased blood ketone bodies, and conservation o f protein tissues. It was hypothesized that these spontaneous and facu ltative hibernators use fat and protein differently during a fast prio r to the hibernation season. Weekly blood and urine samples were taken from both species during a 5-wk period of food and water deprivation. The black-tailed prairie dog lost mass at a greater rate and had a la rger daily urine volume and urea, ammonia, and potassium excretion, as well as a higher plasma urea/creatinine ratio, all of which define a greater rare of protein catabolism for this species than for the white -tailed prairie dog. The black-tailed prairie dog, therefore, does not conserve protein to the same extent as the white-tailed prairie dog d uring a Phase II fast typical of hibernation starvation. Ketone bodies do not appear to regulate protein catabolism directly. But the greate r protein catabolism by the black-tailed prairie dog may be related to pH and water balance requirements that are circumvented in the white- tailed prairie dog by engaging in spontaneous torpor. Both species evo lved from populations of ancestral prairie clogs that have retained th e ability to hibernate spontaneously. It is hypothesized that the blac k-tailed prairie dogs may not have maintained the capacity for a deep Phase II, protein-conserving state typical of hibernation starvation b ut keep an active profile throughout winter, relying to a greater exte nt on protein catabolism in response to selective pressures of greater predation, higher food abundance, and perhaps a need to preserve fat stores for reproduction.