Correlates versus predictors of courtship success: courtship song in Drosophila silvestris and D-heteroneura

Males of the picture-winged flies Drosophila silvestris is and D. heteroneura produce a sound during courtship wing vibration; successful courtships include more time spent in wing vibration. We clipped male wings to test whether this sound is a necessary signal for the success of male courtship. We tested females in no-choice tests and also in choice tests in which each female was provided with a clipped and normal male simultaneously. We found no differences in the probability of copulation for either species in no-choice tests, and no difference for the choice tests with D. heteroneura. Surprisingly, clipped males were significantly more successful than control males in the choice tests with D. silvestris. The latencies to copulate did not differ by treatment in any tests. Consequently, the sound produced by courtship wing vibration does not influence male mating success and thus does not meet the most important criterion for being a sexual signal. We propose that the vibration of thoracic muscles, transmitted through the substrate or through the male's forelegs, could provide a sexual signal in these species. (C) 1997 The Association for the Study of Animal Behaviour.