The Darwinian fitness of mammals living in a rhythmic environment depends on endogenous daily (circadian) rhythms in behavior and physiology. Here, we discuss the mechanisms underlying the circadian regulation of physiology and behavior in mammals. We also review recent efforts to understand circadian flexibility, such as how the phase of activity and rest is altered depending on the encountered environment. We explain why shifting activity to the day is an adaptive strategy to cope with energetic challenges and show how this can reduce thermoregulatory costs. A framework is provided to make predictions about the optimal timing of activity and rest of non-model species for a wide range of habitats. This Review illustrates how the timing of daily rhythms is reciprocally linked to energy homeostasis, and it highlights the importance of this link in understanding daily rhythms in physiology and behavior.
The authors declare no competing or financial interests.
This work was supported by a Dutch Technology Foundation STW grant ‘OnTime’ 12185 to R.A.H. and an Ubbo Emmius scholarship to S.J.R., awarded by the faculty of Mathematics and Natural Sciences, University of Groningen.
- © 2017. Published by The Company of Biologists Ltd