A sexually dimorphic flight muscle functions in the generation of Drosophila male courtship song. Troy Shirangi, David Stern, James Truman. JFRC/HHMI, Ashburn, VA.

   Insects often utilize multiple acoustic signals to organize social interactions. Drosophila melanogaster males, for example, court females by vibrating a wing to produce two types of songs: trains of pulses and bursts of continuous tone called sine song. Currently, it is not known how the Drosophila nervous system generates the individual song types. Moreover, the neuromuscular mechanisms that generate courtship song have not been elucidated. Here, we identify a thoracic motoneuron in Drosophila melanogaster whose inactivation ablates sine song yet leaves pulse song unaffected. This motoneuron innervates a single, male-enlarged flight muscle, hg1, whose sexually dimorphic development is required specifically for maximal sine song amplitude. Furthermore, we demonstrate that males lacking sine song court females less effectively than do normal males. These results define hg1 and its motoneurons as a critical motor unit controlling sine song, provide insights into how the individual components of Drosophila song are generated, and set the stage to decipher the upstream neurons in the circuitry for sine song.