Drosophila song as a species-specific mating signal and the behavioural importance of Kyriacou & Hall cycles in D. melanogaster song

Abstract

‘Species-specific’ mating signals may not make a significant contribution to sexual isolation if differences between species are not matched by narrowly tuned differences in female preferences. The courtship song of the melanogaster species group of Drosophila has been studied by several researchers as a potential factor in sexual isolation, but there are few clear demonstrations that species differences are behaviourally significant. We played synthetic song with typical pulse interval parameters for D.melanogaster, D.simulans orD.sechellia to D.melanogaster or D.simulans females in the presence of mute males. Females mated most quickly when stimulated by song typical of their own species, confirming that song can influence sexual isolation between these species. This effect was greater in D.melanogaster than D.simulans, which correlates with reduced variability in mean interpulse interval within D.melanogaster. We also examined the role of ‘Kyriacou & Hall cycles’ (periodic cycling of mean interpulse intervals) in D.melanogaster. Contrary to some predictions, the presence of the Kyriacou & Hall cycle was more important in increasing mating speed than the increased variability of interpulse intervals that is inevitably present in song containing a cycle. The large stimulatory effect of cycles on mating speed is curious, given that the periodicity of cycles would probably be difficult for females to detect during courtship in field conditions.