The @entity1 circadian system synchronizes daily timing of activity and rest with the environmental light-dark cycle. Although the underlying molecular oscillatory mechanism is well studied, factors that influence phenotypic plasticity in daily activity patterns (temporal niche switching, chronotype) are presently unknown. Molecular evidence suggests that metabolism may influence the circadian molecular @entity16067 , but evidence at the level of the organism is lacking. Here we show that a metabolic challenge by cold and hunger induces diurnality in otherwise nocturnal @entity19 . Lowering ambient temperature changes the phase of circadian light-dark entrainment in @entity19 by increasing daytime and decreasing nighttime activity. This effect is further enhanced by simulated food shortage, which identifies metabolic balance as the underlying common factor influencing circadian organization. @entity16067 gene expression analysis shows that the underlying neuronal mechanism is downstream from or parallel to the main circadian pacemaker (the hypothalamic suprachiasmatic nucleus) and that the behavioral phenotype is accompanied by phase adjustment of peripheral tissues. These findings indicate that nocturnal mammals can display considerable plasticity in circadian organization and may adopt a diurnal phenotype when energetically challenged. Our previously defined circadian thermoenergetics hypothesis proposes that such circadian plasticity, which naturally occurs in nocturnal mammals, reflects adaptive maintenance of energy balance. Quantification of energy expenditure shows that diurnality under natural conditions reduces thermoregulatory costs in small burrowing mammals like @entity19 . Metabolic feedback on circadian organization thus provides functional benefits by reducing energy expenditure. Our findings may help to clarify relationships between @entity25 and metabolic phenotypes in @entity1 .

Cold and hunger induce diurnality in a nocturnal XXXX .

@entity1 :: ('9606', 'Species') :: ['mammalian', 'humans'] @entity19 :: ('10090', 'Species') :: ['mice'] @entity25 :: ('MESH:D012893', 'Disease') :: ['sleep-wake patterns'] @entity16067 :: ('9575', 'Gene') :: ['Clock', 'clock']
@entity1 :: (9606,Species) :: ['mammal']
