Abstract
The tuco-tuco Ctenomys aff. knighti is a subterranean rodent which inhabits a semi-arid area in Northwestern Argentina. Although they live in underground burrows where environmental cycles are attenuated, they display robust, 24 h locomotor activity rhythms that are synchronized by light/dark cycles, both in laboratory and field conditions. The underground environment also poses energetic challenges (e.g. high-energy demands of digging, hypoxia, high humidity, low food availability) that have motivated thermoregulation studies in several subterranean rodent species. By using chronobiological protocols, the present work aims to contribute towards these studies by exploring day-night variations of thermoregulatory functions in tuco-tucos, starting with body temperature and its temporal relationship to locomotor activity. Animals showed daily, 24 h body temperature rhythms that persisted even in constant darkness and temperature, synchronizing to a daily light/dark cycle, with highest values occurring during darkness hours. The range of oscillation of body temperature was slightly lower than those reported for similar-sized and dark-active rodents. Most rhythmic parameters, such as period and phase, did not change upon removal of the running wheel. Body temperature and locomotor activity rhythms were robustly associated in time. The former persisted even after removal of the acute effects of intense activity on body temperature by a statistical method. Finally, regression gradients between body temperature and activity were higher in the beginning of the night, suggesting day-night variation in thermal conductance and heat production. Consideration of these day-night variations in thermoregulatory processes is beneficial for further studies on thermoregulation and energetics of subterranean rodents.
Highlights
24 h rhythmic variations in body temperature (Tb) are found in most mammals studied to date [1] and result from the association between daily rhythms of body heat ‘‘production’’ and heat ‘‘loss’’ [2,3]
These might be adaptive for homoeothermic surface-dwellers, which face the daily challenge of maintaining their Tb within narrow limits, in an environment where ambient temperature varies on a day-night basis [4]
Tb rhythm was strongly associated with motor activity rhythms, with identical period and stable phase relationship
Summary
24 h rhythmic variations in body temperature (Tb) are found in most mammals studied to date [1] and result from the association between daily rhythms of body heat ‘‘production’’ (endogenous increase of Tb) and heat ‘‘loss’’ (due to thermal conductance changes) [2,3]. These might be adaptive for homoeothermic surface-dwellers, which face the daily challenge of maintaining their Tb within narrow limits, in an environment where ambient temperature varies on a day-night basis [4].
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