The Effect of Mating and the Male Sex Peptide on Group Behaviour of Post-mated Female Drosophila melanogaster.

Sleep is a highly conserved state in animals, but its regulation and physiological function is poorly understood. Drosophila melanogaster is an excellent model for studying sleep regulation and has been used to investigate how sex and social interactions can influence wake-sleep profiles. Previously we have shown that copulation has a profound effect on day time activity and quiescence (siesta sleep) of individual post-mated females. Here we have the studied the effect of mating and the transfer of the 36 amino acid sex peptide in the seminal fluid on the behavior of mated female Drosophila populations, where there will be on-going social interactions. The locomotor activity and sleep patterns of virgin and post-mated female D. melanogaster from three laboratory strains (Oregon-R, Canton-S and Dahomey) were recorded in social groups of 20 individuals in a 12-12 h light-dark cycle. Virgin female populations from all three fly strains displayed consolidated periods of low activity in between two sharp peaks of activity, corresponding to lights-on and lights-off. Similar light-correlated peaks were recorded for the mated female populations, however, the low afternoon activity and siesta seen in virgin populations was abolished after mating in all three strains. In contrast, night activity appeared unaffected. This post-mating effect was sustained for several days and was dependent on the male SP acting as a pheromone. Evidence from mixed populations of virgin and mated females suggests that the siesta of non-mated females is not easily disturbed by the presence of highly active post-mated females.