Meeting Abstract

94.5  Wednesday, Jan. 7  Circadian rhythms in free-living arctic ground squirrels. BARNES, BM; Univ of Alaska, Fairbanks ffbmb@uaf.edu

The persistence and function of circadian rhythms in hibernators is controversial. Hibernating mammals withdraw from the environment and undergo profound changes in body temperature (Tb), yet individuals require and demonstrate precise seasonal timing. We are examining expression of circadian and seasonal rhythms in free-living arctic ground squirrels under arctic field conditions by use of internal temperature-sensitive dataloggers and telemetry collars that indicate the timing of use of burrows. Prior to immergence into their hibernacula, ground squirrels showed robust diurnal rhythms of Tb and activity. After ground squirrels become sequestered in their dark burrows but prior to becoming heterothermic, circadian rhythms in Tb continued, but with lower amplitudes, declining averages, and freerunning periods. In some animals, indications of a circadian signal occurred during entry into the first torpor bout, but during the next 5-7 months there were no circadian or other rhythms expressed during torpor or during euthermic phases of arousal episodes. In spring after males resume euthermy but remain in their burrows for 1-3 weeks, the lack of circadian organization continued. Circadian (diurnal) rhythms abruptly resumed when animals first emerged on the surface. Throughout the active season, diurnal rhythms of Tb and activity remained remarkably well entrained to 24 h, despite 3 months without sunrise or sunset. We suggest that expression of circadian timing in arctic ground squirrels is suppressed during hibernation and reactivated in spring on first exposure to light. Thus timing of arousal episodes and termination of hibernation requires mechanisms separate from the circadian clock. Entrainment during the arctic summer appears to be sensitive to subtle light cues and may act to synchronize activity to minimize thermoregulatory costs.