Many animals exhibit an astonishing ability to form groups of large numbers of individuals. The dynamic properties of such groups have been the subject of intensive investigation. The actual grouping processes and underlying neural mechanisms, however, remain elusive. Here, we established a social clustering paradigm in Drosophila to investigate the principles governing social group formation. Fruit flies spontaneously assembled into a stable cluster mimicking a distributed network. Social clustering was exhibited as a highly dynamic process including all individuals, which participated in stochastic pair-wise encounters mediated by appendage touches. Depriving sensory inputs resulted in abnormal encounter responses and a high failure rate of cluster formation. Furthermore, the social distance of the emergent network was regulated by ppk-specific neurons, which were activated by contact-dependent social grouping. Taken together, these findings revealed the development of an orderly social structure from initially unorganised individuals via collective actions.

Age-dependent ectopic fat accumulation (EFA) in animals contributes to the progression of tissue aging and diseases such as obesity, diabetes, and cancer. However, the primary causes of age-dependent EFA remain largely elusive. Here, we characterize the occurrence of age-dependent EFA in Drosophila and identify HDAC6, a cytosolic histone deacetylase, as a suppressor of EFA. Loss of HDAC6 leads to significant age-dependent EFA, lipid composition imbalance, and reduced animal longevity on a high-fat diet. The EFA and longevity phenotypes are ameliorated by a reduction of the lipid-droplet-resident protein PLIN2. We show that HDAC6 is associated physically with the chaperone protein dHsc4/Hsc70 to maintain the proteostasis of PLIN2. These findings indicate that proteostasis collapse serves as an intrinsic cue to cause age-dependent EFA. Our study suggests that manipulation of proteostasis could be an alternative approach to the treatment of age-related metabolic diseases such as obesity and diabetes.