Electronic Thesis and Dissertation Repository


Master of Science




Staples, James F.

2nd Supervisor

McKenzie, Charles A.

Joint Supervisor


Obligate hibernators express circannual patterns of body mass and hibernation, which persist under constant laboratory conditions. I hypothesized that in the 13-lined ground squirrel (Ictidomys tridecemlineatus) thermogenic brown adipose tissue (BAT) and lipid storing white adipose tissue (WAT) volume would follow a circannual pattern. I housed animals at either 25°C (thermoneutral) or 5°C with 12h L:12h D photoperiods for an entire year. I determined volume and water-fat ratio of WAT and BAT using magnetic resonance imaging (MRI). BAT volume follows a circannual pattern in both conditions, increasing prior to winter, decreasing in late winter with no change in water-fat ratio. Both body mass and WAT volume of cold-housed animals declined throughout the winter and recovered after hibernation. By contrast, thermoneutral housing produced no circannual pattern in body mass even though WAT volume declined in late winter. Warm-housed animals never entered torpor indicating that they might not be obligate hibernators.

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