Fig 1. A schematic of ways in which individuals may alter behavior during social interaction.

(A) A hypothetical ethogram and behavioral density for a lone fly (blue). (B) Ethograms and behavioral frequency in the presence of a social partner when the two flies synchronize their behaviors in time. (C) The presence of the second fly alters the frequency of the different behaviors without synchronization. (D) A new social behavior (#4) arises in the presence of the partner.