Goodwin oscillator model explains different response of circadian rhythms to constant light

Light is the most important time-giver of the external environment for the circadian rhythms of organisms. Under different light conditions, changes in the rhythmic behavior of organisms are observed. When exposed to constant light, amplitude suppression was observed in wild-type strains of the microbe Neurospora, whereas the period of the circadian rhythms was shortened in vivid strains. In this study, an explanation was given for these observations by the Goodwin model. It is assumed that the degradation rate of the circadian oscillator in Neurospora differs between strains. We found that with a lower degradation rate, the larger constant light intensity leads to the suppression of amplitude. The low or moderate degradation rate results in a negative relationship between the oscillator period and constant light intensity. In addition, the analytical solutions explored by the asymptotic techniques confirmed our simulation results. This article sheds light on the mechanisms of light affecting the circadian clock as well as the analytical solutions were exhibited for both the period and the amplitude of the clock.