Meeting Abstract
Circadian rhythms are ~24h-long endogenous cycles of physiology and behavior that are thought to be principally entrained by external light cues of dawn and dusk. Constant sunlight during the arctic summer leads to the loss of circadian rhythmicity for some resident animals. Arctic ground squirrels, however, maintain daily rhythms despite constant light during the polar day. We investigated the capacity of arctic ground squirrels to re-entrain their circadian rhythms under conditions of constant daylight after their circadian clocks were phase-shifted by an artificial light:dark cycle while temporally in captivity. Control animals were maintained in an environmental chamber for 28 days with lights on between 8:00 and 21:00, when they are typically aboveground. In contrast, experimental animals received two 6h phase delays such that lights were on between 20:00 and 9:00 for the 14 days prior to their release. Control animals remained entrained to the light cues while in the chamber and after release whereas rhythms of body temperature (Tb) in experimental animals free-ran with a period <24h until they were ~12h out of phase with controls. Within 3d of their release back into the natural environment, however, experimental animals had shifted their rhythms of Tb and behavior (time aboveground and movement) to match that of controls. Our results demonstrate that arctic ground squirrels are able to rapidly resynchronize their rhythms of physiology and behavior after a phase shift despite exposure to constant sunlight.
