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Temperature Dependence of Circadian Rhythms in Golden-Mantled Ground Squirrels

Department of Psychology, University of California, Berkeley, California 94720

Warren G. Homes

Department of Psychology, University of California, Berkeley, California 94720

Irving Zucker

Department of Psychology, University of California, Berkeley, California 94720

We tested the hypothesis that the free-running period and phase angles of entrainment of circadian locomotor activity rhythms of golden-mantled ground squirrels (Spermophilus lateralis) vary as a function of body temperature (T_b). Animals were maintained in a light-dark cycle (LD 14: 10), and at 6-week intervals ambient temperature (Ta) was changed from 20° to 30°C, or vice versa. Data were collected during the animals' homeothermic and heterothermic phases. Subsequently, squirrels were housed in dim constant illumination with the same alternating temperature sequence. In heterothermic ground squirrels (those capable of T_b < 34°C), a decrease in T_a from 30° to 20°C caused phase delays in activity onset, phase advances in activity termination, and a decrease in duration of the active phase; increases in T_a from 20° to 30°C produced the opposite effect on each of these parameters. The free- running period of the activity rhythm of heterothermic squirrels increased and decreased in response to 10°C decreases and increases in T_a, respectively. Changes in T_a did not affect circadian parameters in homeothermic squirrels. Seasonal variations in circadian organization previously observed in this species appear to reflect the influence of endogenous fluctuations in body temperature. Tissue temperature has a major influence on circadian rhythms of golden-mantled ground squirrels.

Journal of Biological Rhythms, Vol. 5, No. 1, 25-34 (1990)
DOI: 10.1177/074873049000500103


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