Abstract
Threat displays are a common form of social communication. In flying species, such displays often involve stereotypical, choreographed wing and leg movements. How the brain coordinates characteristic movements of these appendages to transmit social signals is poorly understood. In male Drosophila, threat displays flexibly combine wing displays with rapid turns and charges. Here we identify two brain modules downstream of a superordinate threat command center. Each contains two neurons that combinatorially generate threat-specific appendicular movements: one comprises two descending neurons synergistically controlling wing threat; the other contains two interneurons that antagonistically control turns and charges. Within-module neuronal coactivation evokes appendage-specific actions recapitulating those evoked by the upstream center. These data uncover a hierarchical combinatorial circuit that coordinates wing and leg movements during a terrestrial social display. More generally, our findings identify an instantiation of a Tinbergenian hierarchical behavioral control system for social communication and reveal a novel underlying implementation logic.