Relationship between the daily rhythms of locomotor activity and body temperature in eight mammalian species

The relationship between the daily rhythms of locomotor activity and body temperature was studied by telemetry in four nocturnal and four diurnal mammalian species. The results showed that the two rhythms are very closely synchronized, as they 1) ascend past the daily mean at the same time, 2) reach the daily acrophase at the same time, and 3) are best correlated at time lags approaching zero. The rhythms of nocturnal animals crossed the daily mean at the transition between the light and dark phases of the light-dark cycle and reached their acrophases during the dark phase, whereas the rhythms of diurnal animals crossed the daily mean at the transition between the dark and light phases and reached their acrophases during the light phase. Despite the close synchrony of the two rhythms, the results indicate that the temperature rhythm is not a byproduct of the activity rhythm, as body temperature during the active phase of the daily cycle was higher than body temperature during the inactive phase in all species irrespective of the activity level prevailing during each phase.