Influencer in flies: Socially interactive individuals shape group-level characteristics

Group living is a widespread adaptive strategy observed across the animal kingdom. Social interactions between individuals within a group often promote behavioral conformity, forming group-level characteristics that correspond to the groups phenotypic and genotypic composition. However, for large-scale groups observed in non-social invertebrates, a theoretical framework establishing how genotypic composition influences group-level characteristics and their intergroup variation has not been verified. Here, we elucidated the mechanism governing activity conformity in multiple Drosophila strains. Furthermore, by combining various strains, we revealed the mechanism by which group-level characteristics are formed as a function of genotype composition. In single-strain groups, image analysis and causal analysis based on information theory revealed that all strains conformed their walking behavior to others behavior. In contrast, mixed-strain groups exhibited emergent group-level characteristics, with some individuals from certain strains displaying non-conforming behavior. Interestingly, these individuals exhibited high sociality and exerted strong social influence on others, suggesting that specific individuals (genotypes) acting as "influencers" within the group plays a crucial role in shaping group-level characteristics. In the wild, each group may develop phenotypic variation influenced by the presence of these individuals.