Energetic relationships between field and laboratory woodchucks (Marmota monax) along a latitudinal gradient

Abstract

Hibernation is a strategy for energy conservation during periods of low food availability, but has energetic costs associated with arousal and maintenance of core body temperature above ambient temperature. Animals hibernating at low ambient temperatures generally exhibit low metabolic rates and reduced body mass loss, but little is known how these energetic costs differ in a single species in varying environments and temperatures. Also, it is unknown how populations along an extreme latitudinal gradient may alter energetic costs in a common environment. We investigated three free-living populations of woodchucks (Marmota monax) along a latitudinal gradient in the United States. In addition, animals obtained from the same three field populations were studied in the laboratory under a “common garden experimental design” to determine whether trends in energetic costs would be maintained. Based on calculated metabolic rates and body mass loss, animals from the northern most latitude exhibited a significantly higher total energetic cost (mlO2/g) over the hibernation season, but a significantly lower cost per day, compared with animals from more southern latitudes. Results from laboratory animals showed similar trends to those found in the field. However, the calculated energetic costs of hibernation in the laboratory were less than the freeliving populations. Energetic cost was compared among the laboratory populations during a period when food was removed and ambient temperature was 5 °C. The southern latitude population was torpid the least amount of time and incurred the highest energetic cost. We conclude that latitude has a significant effect on the energetic costs of hibernation.