Abstract
Several rodent species that are diurnal in the field become nocturnal in the lab. It has been suggested that the use of running-wheels in the lab might contribute to this timing switch. This proposition is based on studies that indicate feed-back of vigorous wheel-running on the period and phase of circadian clocks that time daily activity rhythms. Tuco-tucos (Ctenomys aff. knighti) are subterranean rodents that are diurnal in the field but are robustly nocturnal in laboratory, with or without access to running wheels. We assessed their energy metabolism by continuously and simultaneously monitoring rates of oxygen consumption, body temperature, general motor and wheel running activity for several days in the presence and absence of wheels. Surprisingly, some individuals spontaneously suppressed running-wheel activity and switched to diurnality in the respirometry chamber, whereas the remaining animals continued to be nocturnal even after wheel removal. This is the first report of timing switches that occur with spontaneous wheel-running suppression and which are not replicated by removal of the wheel.
Highlights
The tuco-tuco (Ctenomys aff. knighti), a South American subterranean rodent, is among the several mammals described as having discrepant activity timing between field and laboratory conditions [1,2,3,4,5,6,7]
We report the first displays of diurnality in the lab, which occurred exclusively during our respirometry experiment (Fig 1)
The search for the critical factors which trigger the nocturnality/diurnality switch observed in other species often converge upon the issue of the meaning of the running-wheel activity in the laboratory [34,35,36,37]
Summary
The tuco-tuco (Ctenomys aff. knighti), a South American subterranean rodent, is among the several mammals described as having discrepant activity timing between field and laboratory conditions [1,2,3,4,5,6,7]. Knighti), a South American subterranean rodent, is among the several mammals described as having discrepant activity timing between field and laboratory conditions [1,2,3,4,5,6,7]. Differences in energy demand between field and laboratory conditions could be the fundamental feature leading to inversion in the timing of daily activity [7,11,17].
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