Effects of Light and Ambient Temperature in a Diurnal Rodent, the Nile Grass Rat

Changes in environmental conditions often result in changes in the display of circadian rhythmicity and locomotor activity levels of mammals. In previous experiments, day active (diurnal) grass rats (Arvicanthis niloticus) have been shown to switch to a night active (nocturnal) pattern of activity after the introduction of a running wheel. However, it is not yet known the mechanism by which animals switch from being diurnal to nocturnal. Here, we used grass rats to examine activity levels following manipulations of varying ambient temperatures and lighting intensities. Animals were singly housed with running wheels and data were collected in 12:12 light-dark (LD) conditions. First, we examined how a warmer ambient temperature during the day (25 degrees Celsius) and a cooler night (21 degrees Celsius) would affect wheel running activity. We found that 100% of grass rats in this condition were diurnal. The ambient temperature was then raised to a warmer condition (constant 32 degrees Celsius). Diurnality was still expressed by 100% of the subjects following the temperature increase, yet overall wheel running activity significantly decreased (p \u3c .05). Next, we plan to adjust the ambient temperature to a colder condition. We predict that grass rats will maintain diurnal patterns of activity in cold conditions, but will exhibit higher overall wheel running activity. Finally, we plan to adjust the room temperature back to a baseline temperature of 25 degrees Celsius, and dim the intensity of light in the environment. Altogether, we predict that changes in ambient temperatures will affect overall activity levels while maintaining diurnality, whereas changes in lighting intensity will affect the display of diurnal activity patterns. Our results will allow us to predict how lighting and temperature maintain diurnality, which is important in light of the growing evidence that humans that become night-active have significant health consequences