Meeting Abstract
Circadian systems provide animals with the ability to coordinate their physiological and metabolic functions in anticipation of predictable daily changes in their environment. However, whether circadian rhythms persist during hibernation is contentious. We hypothesized that circadian clocks are arrested during hibernation and that the post-hibernation resumption of rhythmicity is triggered by exposure to light when ground squirrels first emerge to the surface. We investigated the association between timing of emergence and resumption of body temperature (Tb) rhythms in free-living arctic ground squirrels and experimentally assessed the responsiveness of rhythmicity by manipulating light exposure and hibernation in animals in the lab. During deep torpor, Tb of squirrels was arrhythmic within the 0.02ºC resolution of our data loggers and remained arrhythmic in males returning to high Tb in spring but remaining in their burrows for up to 3 weeks; Tb rhythms re-emerged coincident with emergence from the hibernacula, though some individuals developed weak, but significant, rhythms following exposure to low-intensity light from within the hibernacula. Squirrels maintained in the lab in constant darkness spontaneously developed weak, but significant, body temperature rhythms within three weeks of terminating hibernation. Individuals exposed to a 5-second pulse of light within 5 days of terminating hibernation, however, immediately developed robust circadian Tb rhythms. Our results are consistent with the hypothesis that low Tb during torpor inhibits clock function. Exposure to light following hibernation may be accelerating the resumption of circadian Tb rhythms by synchronizing loosely coupled circadian oscillators within the suprachiasmatic nucleus.
