Weekday-Weekend Shifts of Light/Dark Regimen Extend Sleep and Lifespan of Drosophila melanogaster

Purpose: Daytime workers/learners report reduction of sleep duration on weekdays. However, this reduction can be partially compensated by an advance in circadian sleep timing caused by an advance in the phase of the circadian clock. This advance occurs in response to an advance in the 24-h pattern of exposure to light emitted by natural and artificial light sources. It is difficult to separate health impacts of weekday sleep reduction and weekday-weekend shifts in the circadian phase in human studies. Therefore, an animal model can be used to clarify the impact of these shifts. A limited number of previous studies on insects and rodents have yielded conflicting results. We used a Drosophila model to document the effects of weekday-weekend shifts in the dark-light cycle on sleep, development, and survival. Methods: Locomotor activity and sleep, fecundity, rate of imago emergence, and longevity were assessed under two pairs of control and experimental conditions in two generations of flies from two melanogaster strains with faster and slower speeds of the aging process, Harwich and Canton-S, respectively. Results: At least in one of these two pairs with the 4-h weekday-weekend shifts in the light/dark regimen as experimental condition, significant differences from the control condition were documented for the levels of locomotor activity and sleep, rate of development from eggs to imago, and longevity. In this experimental condition, two generations of Canton-S but not Harwich flies slept longer on weekdays than the control flies. Moreover, flies of both strains developed longer to imago stage and lived longer than the control flies in this experimental condition. Overall, any of such differences between conditions in lifespan and sleep were beneficial for the experimental flies. Conclusion: It is unlikely that the light-induced 4-h weekday-weekend shifts in circadian timing are detrimental to survival, reproductive health, and sleep in Drosophila melanogaster . Plain Language Summary: Weekday sleep duration is reduced in daytime workers/learners. This reduction can be partially compensated by an advance in circadian sleep timing caused by an advance in the phase of the circadian clock in response to an advance in the 24-h pattern of exposure to light emitted by natural and artificial light sources. Both weekday sleep reduction and weekday-weekend shifts in the circadian phase have been proposed to negatively impact health. However, it is difficult to separate their impacts in human studies. Therefore, an animal model can be used to clarify the impact of weekday-weekend shifts of the circadian sleep phase on sleep, reproductive health, and survival. We examined the effects of weekday-weekend shifts in the 24-h light/dark schedule on locomotor activity and sleep, fecundity, rate of development from eggs to imago, and longevity of fruit flies from two strains with faster and slower speeds of the aging process (Harwich and Canton-S, respectively). The results suggest that the daily levels of locomotor activity and sleep, development from eggs to imago, and longevity can be significantly changed in response to the 4-h weekday-weekend shifts in the light/dark regimen. Paradoxically, such changes are beneficial for weekday sleep duration in one of the strains (Canton-S) and for rate of development and lifespans in both strains. We concluded that, at least in the absence of additional stressors, the light-induced the 4-h weekday-weekend shifts of the circadian phase seem not to be detrimental to fly’s sleep, reproductive health, and survival. Keywords: animal model, fruit fly, life span, fertility, sleep duration, sleep-wake regulating processes