Temperature-Independence of Circannual Variations in Circadian Rhythms of Golden-Mantled Ground Squirrels

Abstract

In golden-mantled ground squirrels, phase angles of entrainment of circadian locomotor activity to a fixed light-dark cycle differ markedly between subjective summer and winter. Achange in ambient temperature affects entrainment only during subjective winter when it also produces pronounced effects on body temperature (T_b). It was previously proposed that variations in T_b are causally related to the circannual rhythm in circadian entrainment. To test this hypothesis, wheel-running activity and T_b were monitored for 12 to 14 months in castrated male ground squirrels housed in a 14:10 LD photocycle at 21 °C. Animals were treated with testosterone implants that eliminated hibernation and prevented the marked winter decline in T_b; these squirrels manifested circannual changes in circadian entrainment indistinguishable from those of untreated animals. Both groups exhibited pronounced changes in phase angle and alpha of circadian wheel-running and T_b rhythms. Seasonal variation in T_b is not necessary for circannual changes in circadian organization of golden-mantled ground squirrels.

Keywords

circannual rhythm circadian rhythm body temperature circadian entrainment golden-mantled ground squirrel torpor hibernation testosterone

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