Circadian Rhythms: Insights from Mathematical Models

Circadian oscillations are universal, controlling 24-hour rhythms of metabolism, physiology and behaviour in organisms ranging from humans to cyanobacteria. The circadian clock controls the expression of many genes, in a proportion between 10% (in the fruit fly) and 100% (in cyanobacteria). Circadian rhythms share similar basic properties – they can be entrained by light and temperature signals, for example. Temperature is interesting as an environmental time cue as, on the one hand, the clock is sensitive to temperature to the extent that it can act as an entraining signal, while on the other it is insensitive in that the period of the rhythm is largely invariant across the physiological temperature range. This latter phenomenon (temperature compensation) is one of the defining properties of the clock, and recent work has suggested that the small variation observed is a specific, adaptive control of period which contributes to the seasonal adjustment of entrainment phase.