Auditory sensitivity, spatial dynamics, and amplitude of courtship song in Drosophila melanogaster

Acoustic communication is an important component of courtship in Drosophila melanogaster. It takes the form of courtship song produced by males through the unilateral extension and vibration of a wing. Following the paradigm of sender-receiver matching, song content is assumed to match tuning in the auditory system, however, D. melanogaster audition is nonlinear and tuning dependent upon signal amplitude. At low stimulus amplitudes or in the absence of sound the antenna is tuned into song frequency, but as amplitude increases the antenna's resonance is shifted up by hundreds of Hertz. Accurate measurements of song amplitude have been elusive because of the strong dependency of amplitude upon the spatial geometry between sender and receiver. Here, D. melanogaster auditory directional sensitivity and the geometric position between the courting flies are quantified. It is shown that singing occurs primarily from positions resulting in direct stimulation of the female antenna. Using this information, it is established that the majority of song is louder than theoretically predicted and at these sound levels the female antenna should not amplify or be tuned into song. The study implies that Drosophila hearing, and, in particular, its active mechanisms, could function in a broader context than previously surmised.