Circadian clocks regulate the physiology and behaviour of organisms across a wide range of taxa. To keep track of local time, these clocks use a variety of time cues such as light-dark, temperature, food availability and social interaction cycles. This study assessed the role of social cues in modulating circadian clocks of the fruit fly Drosophila melanogaster. Using pair-wise interactions, we first estimated the percentage contribution of each interacting partner on the cumulative rhythmic behaviour of the pairs. Subsequently, we studied the effects of multi-individual (group-wise) interactions on the rhythmic behaviour of the group by estimating phase synchrony between individuals of different strains (having different circadian periods) maintained in both homogeneous and heterogeneous groups. Although it is known that social interactions improve synchrony between interacting individuals, we asked whether such interactions are able to synchronize the circadian rhythms of highly phase-desynchronized flies. We found that, although interactions between fly strains possessing different circadian periods failed to produce synchrony, social interactions among phase-desynchronized flies did enhance the phase synchrony of the interacting individuals. Differently phased individuals living in social groups displayed significantly greater phase synchrony than those living solitarily. Social synchronization is olfaction mediated as group-wise interactions among phase-desynchronized flies possessing compromised olfactory ability (Or83b(0)) did not improve phase synchrony. These results suggest that social cues synchronize the circadian clocks of Drosophila provided that the interacting individuals have similar clock periods.
