The effect of light intensity on the circadian rhythms of eclosion in Drosophila pseudoobscura

Abstract

1. The circadian system in Drosophila pseudoobscura responds to a non-recurrent change in light intensity in the same manner as to transitions from light to darkness or from darkness to light. 2. This simulation of the light "on" effect and light "off" effect by light intensities is more efficient when the ratio between the acclimation light intensity and the subsequent test light intensity is higher. 3. The rhythms initiated by the onset of light and continuing in it tend to wane after three or four cycles. Rhythms initiated by onset of darkness and free running in it are persistent over longer periods and better synchronized. In both cases, however, the system undergoes a transient of one cycle in duration. 4. The implications of these observations in the context of earlier work by other authors is discussed.