Simulating Season: The Effects of Photoperiod and Temperature on Thermogenesis in Deer Mice

Abstract

Ambient temperature is known to drive changes in the thermal physiology of mammals, such as an increase in the capacity for thermogenesis in winter. Previous work has shown that acclimation to chronic cold increases the capacity for non-shivering thermogenesis (NST) and thermogenic capacity (cold-induced maximal oxygen consumption, V̇O2max) in deer mice (Peromyscus maniculatus). Photoperiod, is an important driver of seasonal changes in physiology. In the wild, animals are attuned to seasonal changes in temperature and photoperiod. However, the independent and combined effects of temperature and photoperiod on the capacity for NST in small mammals, such as the deer mouse, are still not fully understood. To address this, we acclimated deer mice to long or short photoperiods (12h or 8h light), in either thermoneutral or cold conditions (30°C or 5°C). To simulate the fall conditions in their natural habitat (Nebraska) we gradually reduced either daylength, temperature, or both over 4 weeks and acclimated mice an additional 4 weeks at those conditions. After the 8 weeks of acclimation, we determined NST and V̇O2max. We found that cold and short photoperiod were necessary to increase NST, and either short photoperiod or cold was sufficient to increase V̇O2max. There were no corresponding differences in iBAT mass, lipid droplet morphology, nor in mitochondrial content. However, there was a corresponding increase in UCP1 content per unit mitochondria. These data highlight the importance of both photoperiod and temperature as cues to prepare thermogenic responses beneficial as winter approaches.