Sleep in populations of Drosophila melanogaster Sleep in populations of Drosophila melanogaster

15 The fruit fly Drosophila melanogaster is a diurnal insect active during the day with 16 consolidated sleep at night. Social interactions between pairs of flies have been shown to 17 affect locomotor activity patterns, but effects on locomotion and sleep patterns have not been 18 assessed for larger populations. Here, we use a commercially available Locomotor Activity 19 Monitor (LAM25H) system to record and analyze sleep behavior. Surprisingly, we find that 20 same-sex populations of flies synchronize their sleep/wake activity, resulting in a population 21 sleep pattern which is similar, but not identical to that of isolated individuals. Like individual 22 flies, groups of flies show circadian and homeostatic regulation of sleep as well as sexual 23 dimorphism in sleep pattern and sensitivity to starvation and a known sleep-disrupting 24 mutation (amnesiac). Populations of flies, however, exhibit distinct sleep characteristics from 25 individuals. Differences in sleep appear to be due to olfaction-dependent social interactions 26 and change with population size and sex ratio. These data support the idea that it is possible 27 to investigate neural mechanisms underlying the effects of population behaviors on sleep by 28 directly looking at a large number of animals in laboratory conditions. 29 Significance Statement: Most species live in an interactive environment in their natural 30 habitats, and sleep can be affected by social cues. Although flies have been widely used to 31 understand the mechanisms of sleep in recent years, sleep in large populations has not been 32 systematically studied. Here we report both similarities and differences between sleep in 33 populations of flies compared to individuals as well as provide a new method for the study of 34 social behavior under constant environmental conditions. 35