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 an anorexic state followed by torpor in early fall. The black-tailed prairie dog is a facultative hibernator that enters torpor only when deprived offood and water in the winter. The physiological state of hibernation is similar to a Phase II euthermic fast characterized by elevated fat catabolism, increased blood ketone bodies, and conservation ofprotein tissues. It was hypothesized that these spontaneous and facultative hibernators use fat and protein differently during a fast prior to the hibernation season. Weekly blood and urine samples were taken from both species during a 5-wk period offood and water deprivation. The black-tailed prairie dog lost mass at a greater rate and had a larger daily urine volume and urea, ammonia, and potassium excretion, as well as a higherplasma urea/creatinine ratio, all of which define a greater rate 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 during a Phase Il fast typical of hibernation starvation. Ketone bodies do not appear to regulate protein catabolism directly. But the greater 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 evolved from populations of ancestral prairie dogs that have retained the ability to hibernate spontaneously. It is hypothesized that the black-tailed prairie dogs may not have maintained the capacity for a deep Phase II, protein-conserving state t'pical of hibernation starvation but keep an active profile throughout winter, relying to a greater extent on protein catabolism in response to selective pressures of greaterpredation, higher food abundance, and perhaps a need to preserve fat stores for reproduction. Physiological Zoology 68(5):915-934. 1995. c 1995 by The University of Chicago. All rights reserved. 0031-935X/95/6805-9454$02.00