SYMPOSIUM Re-examining ‘‘Temporal Niche’’

Synopsis The circadian system temporally organizes physiology and behavior throughout the 24-h day. At the core of this organization lies a network of multiple circadian oscillators located within the central nervous system as well as in virtually every peripheral organ. These oscillators define a 24-h temporal landscape of mutually interacting circadian rhythms that is known as the temporal niche of a species. This temporal niche is constituted by the collective phases of all biological rhythms emerging from this multi-oscillatory system. We review evidence showing that under different environmental conditions, this system can adopt different harmonic configurations. Thus, the classic chronobiological approach of searching for ‘‘the’ ’ circadian phase of an animal—typically by studying circadian rhythms of locomotor activity—represents a narrow look into the circadian system of an animal. We propose that the study of hormonal rhythms may lead to a more insightful assessment of a species ’ temporal niche. Temporal niche The circadian system regulates daily oscillations in physiology and behavior, defining a 24-h temporal landscape of mutually interacting biological rhythms across and within organisms. The ‘‘temporal niche’’ of a species is defined as the conjunction of thes