title: The flexible clock: predictive and reactive homeostasis, energy balance and the circadian regulation of sleep-wake timing.
abstract: 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.
authors.affiliation: Groningen Institute for Evolutionary Life Sciences, Chronobiology Unit, University of Groningen, Groningen 9747AG, The Netherlands.
authors.forename: Sjaak J
authors.initials: SJ
authors.lastname: Riede
authors.affiliation: Groningen Institute for Evolutionary Life Sciences, Chronobiology Unit, University of Groningen, Groningen 9747AG, The Netherlands.
authors.forename: Vincent
authors.initials: V
authors.lastname: van der Vinne
authors.affiliation: Groningen Institute for Evolutionary Life Sciences, Chronobiology Unit, University of Groningen, Groningen 9747AG, The Netherlands r.a.hut@rug.nl.
authors.forename: Roelof A
authors.identifier: 0000-0003-4552-0985
authors.initials: RA
authors.lastname: Hut
mesh_terms: D000818:Animals; D001833:Body Temperature Regulation; D002940:Circadian Rhythm; D004734:Energy Metabolism; D006706:Homeostasis; D006801:Humans; D012890:Sleep; D013493:Suprachiasmatic Nucleus / Q000502:physiology*; D013696:Temperature; D014851:Wakefulness
keywords: Adaptation; Circadian rhythm flexibility; Circadian thermo-energetics; Energy homeostasis; Peripheral clock phase