Identification Of Neural Circuit And Molecular Mechanisms For Regulation Of Social Clustering And Social Space In Drosophila

Conspecifics tend to aggregate to form a social group to attain effective social interactions,allowing sharing of resources and defence against predators.Social clustering is a general survival strategy from microorganisms to human beings,which enhances environmental sensing and decision-making in groups of animals.Studies on schooling fish,flocking birds and migrating locusts have demonstrated that simple rules of interactions between individuals contribute to the emergent dynamics of the group.However,limited by available experimental paradigms and applicable manipulations to the animals under study,how interactions between individuals drive the formation of social structures,especially at the molecular and neural circuit levels,are largely unknown.Although Drosophila melanogaster,a common animal model for neuroethology,is considered as a solitary species,a few studies had suggested certain type of innate social behaviors,the self-organized aggregation,exists in the fruit flies.Here,I established a paradigm of collective behavior in Drosophila,to take advantage of the powerful genetic and neuronal manipulation tools and to precisely control the experimental conditions and the animal's physiological states.The wild type flies spontaneously formed an aggregation without any external attractive cues,and the members in the social cluster maintained certain distance,about 1.5-2 body length,from each other.Further investigation showed that this collective behavior highly depends on multiple sensory inputs.The role of olfaction for social aggregation displays a sexual dimorphism,which mediates social aggregation only in females.Analysis on the dynamics of cluster-formation revealed that inter-fly interactions drive the aggregation,while the encounters happening at edge of clusters promoted the growth of the cluster.The mechanosensation played an important role during the dynamic process by mediating pair-wise interactions.Intriguingly,my results demonstrated that the social distance is regulated primarily by the wing-length,which has no effect on the dynamic properties of cluster formation.Last,ppk-specific mechanosensory neurons played important roles in this process as activation of these neurons resulted in shorter social distance,while inactivation of them suppressed the social cluster formation.Together,these findings revealed the driving mechanisms of how an orderly social structure emerges from highly dynamic collective actions of all individuals,and highlighted Drosophila as an appealing model system for unravelling neural basis of collective behavior.