Paired fruit flies synchronize behavior: Uncovering social interactions in Drosophila melanogaster.

Social behaviors are ubiquitous and crucial to an animal's survival and success. The behaviors an animal performs in a social setting are affected by internal factors, inputs from the environment, and interactions with others. To quantify social behaviors, we need to measure both the stochastic nature of the behavior of isolated individuals and how this behavioral repertoire changes as a function of the environment and interactions between individuals. We probed the behavior of male and female fruit flies in a circular arena as individuals and within all possible pairings. By combining measurements of the animals' position in the arena with an unsupervised analysis of their behaviors, we define the effects of position in the environment and the presence of a partner on locomotion, grooming, singing, and other behaviors that make up an animal's repertoire. We find that geometric context tunes behavioral preference, pairs of animals synchronize their behavioral preferences across shared trials, and paired individuals display signatures of behavioral mimicry. Author summary It is often difficult to describe why an animal behaves the way it does. This is particularly true when we watch several animals at once. We can intuit from watching interactions in different species, from humans to insects, that an individual does not behave the exact same way in a social context as when completely alone. One aim of studying social behavior is to discover underlying principles that are responsible for the behaviors we observe. While we know animals communicate and engage each other, summarizing social interactions is difficult because each individual, much less each each grouping of animals, is different. Here we measure the interactions of paired fruit flies in a systematic way, and capture how different social pairings affect the behavior of the animals. We find males and females pay attention to their environments and what their partners do at different distances, and paired individuals tend to synchronize behavior with their partners across all types of pairings.