The Elaborate Postural Display of Courting Flies Produces Substrate-Borne Vibratory Signals.

Sexual selection has led to the evolution of extraordinary and elaborate male courtship behaviors across taxa, including mammals and birds, as well as some species of flies. flies perform complex courtship behaviors found in most species, which consist of visual, air-borne, gustatory and olfactory cues. In addition, courting males also perform an elaborate postural display that is not found in most other species. This postural display includes an upwards contortion of their abdomen, specialized movements of the head and forelegs, raising both wings into a "wing-posture" and, most remarkably, the males proffer the female a regurgitated droplet. Here, we use high-resolution imaging, laser vibrometry and air-borne acoustic recordings to analyse this postural display to ask which signals may promote copulation. Surprisingly, we find that no air-borne signals are generated during the display. We show, however, that the abdomen tremulates to generate substrate-borne vibratory signals, which correlate with the female's immobility before she feeds onto the droplet and accepts copulation.