Locomotor and feeding activity rhythms in a light-entrained diurnal rodent, Octodon degus

The wheel running (WR) and feeding activity (FA) of Octodon degus, a new laboratory rodent characterized by its diurnal habits, were recorded under different lighting conditions. Under 12:12-h light-dark (LD 12:12) cycles, WR activity exhibited a crepuscular pattern with two peaks, M and E, associated with "dawn" and "dusk," respectively. In both cases, an anticipatory activity was patent, suggesting that, beside the masking effect of LD transitions, both peaks have an endogenous origin. This pattern, which was also observed under a skeleton photoperiod (LD 0.5:11.5), became unimodal after LD 0.5:23.5 and constant darkness (DD) exposure. Simultaneously, FA showed an arrhythmic pattern in most animals, especially under DD, when none of the animals exhibited a significant circadian rhythm. The existence of two groups of oscillators, or two oscillators, would explain most properties of the WR rhythms noted in this species. Our results show that the degu's temporal feeding strategy seems mainly arrhythmic, whereas its WR pattern is driven by a strongly circadian bimodal rhythm.