NOCTURNAL ILLUMINATION DIMMER THAN STARLIGHT ALTERED THE CIRCADIAN RHYTHM OF ADULT LOCOMOTOR ACTIVITY OF A FRUIT FLY

Abstract

The effects of nocturnal irradiance tenfold dimmer than starlight intensity on the locomotor activity rhythm of Drosophila jambulina were investigated in two types of light-dark (12 h:12 h) cycles, in which light intensity of the photophase was 10 lux while that of the scotophase was either 0 lux for control flies or 0.0006 lux for experimental flies. Activity onset in the experimental flies was ∼5.4 h prior to lights-on, so it occurred around midnight. However, activity onset of the control flies coincided almost with the lights-on. Nevertheless, activity offset was the same in both groups, occurring at lights-off. Duration of the active phase (α) and activity passes/fly/cycle (APC) in the experimental flies was far greater than in controls. After-effects of the nocturnal illumination of the light-dark cycles when the flies were transferred to constant darkness were evident as the period of the free-running rhythm was shortened, α was lengthened, and APC was enhanced in the experimental compared to control flies. Thus, very low photic sensitivity of these flies appears to be a physiological adaptation to dim-light ambiance in its natural breeding site in the field. (Author correspondence: [email protected])

Keywords:

• Drosophila jambulina
• Light entrainment
• Nocturnal illumination
• Circadian activity rhythm

ACKNOWLEDGMENTS

The authors thank two anonymous referees for the constructive comments on the previous version of the manuscript.

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.