Diurnality in rodents is relatively rare and occurs primarily in areas with low nighttime temperatures such as at high altitudes and desert areas. However, many factors can influence temporal activity rhythms of animals, both in the field and the laboratory. The temporal activity patterns of the diurnal ice rat were investigated in the laboratory with, and without, access to running wheels, and in constant conditions with running wheels. Ice rats appeared to be fundamentally diurnal but used their running wheels during the night. In constant conditions, general activity remained predominantly diurnal while wheel running was either nocturnal or diurnal. In some animals, entrainment of the wheel running rhythm was evident, as demonstrated by free-running periods that were different from 24 h. In other animals, the wheel running activity abruptly switched from nocturnal to subjective day as soon as the animals entered DD, and reverted back to nocturnal once returned to LD, suggesting the rhythms were masked by light. Wheel running rhythms appears to be less robust and more affected by light compared to general activity rhythms. In view of present and future environmental changes, the existence of more unstable activity rhythms that can readily switch between temporal niches might be crucial for the survival of the species.
Supplemental material: Table S1. Dawn and dusk simulation.
Table S2. The mean ( ± SE) of individual animals with and without wheels for the general activity and wheel running activity for light (L; 10 hours) , twilight (T; 4 hours) and dark (D; 10 hours) and the % of activity that is exhibited during each temporal phase. The sex of the animals is indicated with m or f behind the ID. BW = body weight in g.
Table S3. Mean activity counts of individual animals in the light and dark phases of LD and the subjective day and night in DD , for general activity and wheel running activity. The percentage of activity during the light (LD), or subjective day (DD) and the period length (tau) during DD is provided. The sex of the animals is indicated with m or f behind the ID.