Meeting Abstract

58.2  Saturday, Jan. 5  Changes in resting metabolic rate of free-living arctic ground squirrels across the active season. FRIDINGER, R.W.*; TOIEN, O.; BARNES, B.M.; BUCK, C.L.; Univ. of Alaska Anchorage; Univ. of Alaska Fairbanks; Univ. of Alaska Fairbanks; Univ. of Alaska Anchorage asrwf5@uaa.alaska.edu

Arctic ground squirrels (Spermophilus parryii) exhibit an endogenously timed circannual rhythm of energy metabolism, body temperature, mass and condition. During the latter part of the active season, this rhythm is marked by rapid increases in both mass and adiposity as animals prepare to enter hibernation, which lasts for the next 6-9 months. Given the metabolic control that animals exhibit through hibernation, we wanted to investigate if and to what extent their resting metabolic rate (RMR) changes through the active season, particularly in relation to the pre-hibernatory fattening period. This study took place from April-September in 2006 and 2007 in the northern foothills of the Brooks Range, Alaska. Squirrels were trapped and transported to the nearby Toolik Lake Field Station where they were weighed, measured and assessed overnight for RMR using respirometry including rate of CO2 production. Animals were then released at the site of their capture. In 2007, we additionally estimated body composition using the total body electrical conductance method as well as by deuterium labeled water dilution; these analyses are forthcoming. As expected, arctic ground squirrels significantly increased in both mass and adiposity in July and August. During this period, mass specific RMR declined while absolute RMR remained constant or declined slightly concurrent with mass increases of 25-50%. Allometry predicts that mass specific RMR would decrease with increasing mass. However, absolute RMR was expected to increase as animals got larger. No change in RMR with increased body mass is suggestive of metabolic suppression that could contribute to squirrels� ability to achieve an energy surfeit that facilitates rapid weight gain prior to entry into hibernation.