Seasonality and seasons out of time - The thermoregulatory effects of light interference

The change in photoperiod is the main environmental cue for seasonal function of the reproductive, thermoregulatory, and immune systems in rodents existing outside of the tropics. In Israel, the social vole Microlus socialis breeds mainly under short photoperiod (SP) conditions. Previous studies showed that exposing voles to light interference (LI) in the field during the winter resulted in death. The aim of the current study was to determine the thermoregulatory response of SP-acclimated voles to L1. Therefore, heat production (VO(2)) at different ambient temperatures (T(a)) and nonshivering thermogenesis (NST) were measured. Results show that LI of 15 min every 4 h during the dark period significantly (p < 0.02) decreased VO(2) at T(a) = 15 degrees C and significantly (p < 0.05) decreased NST-capacity. These results can at least partly explain why LI-voles died during the winter tinder field conditions, through eliminating winter acclimatization of the thermoregulatory system, or what is considered as seasons out of time.