A Direct Comparison between Circadian and Noncircadian Rhythms in Neurospora crassa

A method has been devised for observing both circadian and noncircadian rhythms in a single wild type strain of Neurospora crassa. This method allows a direct comparison of the properties of the two types of rhythm. The circadian rhythm of conidiation always entrains to a light-dark cycle, damps out in constant light, and has a temperature-compensated period length. The noncircadian rhythm of hyphal branching, expressed by the same strain under different environmental conditions, does not entrain to a light-dark cycle, persists in constant light, and its period length is temperature-dependent. These results suggest that the two rhythms have different underlying mechanisms and demonstrate that the differences in the rhythms previously observed in different strains (patch, band, and clock) are not due to genetic differences between these strains but rather are inherent properties of the rhythms themselves.