Meeting Abstract

50.2  Monday, Jan. 5  Using stable isotopes to track tissue catabolism during hibernation in an extreme arctic hibernator, Spermophilus parryii LEE, Trixie N.*; BUCK, C. Loren; BARNES, Brian M.; O’BRIEN, Diane M.; Univ. of Alaska, Fairbanks; Univ. of Alaska, Anchorage; Univ. of Alaska, Fairbanks; 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 to elucidate the source of lean mass loss during hibernation. Ambient hibernation temperatures of -10C invoke an 8-fold increase in metabolic rate during torpor and a shift toward metabolism of glucose and amino acids. We divided S. parryi hibernating in captivity at 2C into two thermal regimes, -10C (thermally regulating) and 2C (thermally neutral), and measured nitrogen isotope ratios in a suite of tissues collected at the beginning of hibernation and after 45, 68, and 90 days of hibernation. Tissues varied dramatically in nitrogen isotope ratios: organs, including heart, liver, brown adipose tissue, and small intestine, enriched during hibernation while four skeletal muscles did not. The pattern of enrichment differed with thermal stress as animals at -10C were generally more enriched. Plasma reflected organ metabolism while red blood cells remained stable. These results indicate that muscles are not a source of protein during early hibernation. By pairing this knowledge with field measurements of thermal regime, lean mass loss, and isotope enrichment, we hope to arrive at a more complete understanding of protein catabolism and its physiological impact on these extreme hibernators.