Meeting Abstract
48.5 Saturday, Jan. 5 Using stable isotopes to monitor lean mass loss in an extreme hibernator, Spermophilus parryii LEE, Trixie N.**; O’BRIEN, Diane M.; BUCK, C. Loren; BARNES, Brian M.; Univ. of Alaska, Fairbanks; Univ. of Alaska, Fairbanks; Univ. of Alaska, Anchorage; Univ. of Alaska, Fairbanks fttnl@uaf.edu
Arctic ground squirrels (Spermophilus parryii) are small hibernators in the extreme arctic environment. Although lipid is the sole fuel source during hibernation in many species, S. parryii also utilizes considerable amounts of lean mass to meet the high energetic demands of maintaining a large thermal gradient in subzero ambient temperatures. Changes in stable nitrogen isotope ratios can reflect protein metabolism during fasting and may be useful in hibernators as a way of tracking changes in lean mass over winter. We divided S. parryi hibernating in captivity at 2°C into two thermal regimes, -10°C (thermally regulating) and 2°C (thermally neutral), and monitored plasma and red blood cell (RBC) nitrogen isotope ratios. Hibernation temperatures of -10°C invoke an 8-fold increase in metabolic rate during torpor and a shift toward metabolism of glucose and amino acids. As predicted, plasma of hibernators switched to -10°C was significantly enriched in 15N compared to that of animals maintained at 2°C, while nitrogen isotope ratios of RBC�s remained constant over the season and similar between groups. Unexpectedly, plasma nitrogen isotope ratios decreased toward the end of hibernation in both -10°C and 2°C groups, suggesting a change in the source of lean mass used over time. A comparison of nitrogen isotope ratios among tissues of animals in the two temperature treatments is underway to elucidate the source of lean mass loss during hibernation. The importance of the annual lean mass cycle in S. parryii is not well understood, but may play a critical role in overwinter survival in this extreme environment.
