Female preference for artificial courtship songs in 'Drosophila melanogaster' and 'D. simulans'

Abstract

Fertilisation between species may be prevented by differences in their mating systems, if a mating signal of one species is not recognised as such by another species. Closely related species are often most differentiated in their mating systems. Speciation may come about as a consequence of divergence of mating signals and preferences of species. Reinforcement of differences in mating systems may be a consequence of sympatry of sibling species. Understanding mating systems, particularly in terms of how they contribute to reproductive isolation, is therefore central to the study of speciation and animal diversity. Visual, chemical and auditory stimuli are required for mate-recognition in the Drosophila melanogaster complex. Among these stimuli is a species-specific male auditory signal, pulse song. Female preference for conspecific mean interpulse-interval (IPX) and IPI rhythm may contribute towards reproductive isolation of species, and divergence in this aspect of the mating system may be an important cause or effect of speciation of fruit flies. The two chapters of this thesis examine different aspects of female preference for pulse song. The first chapter considers the contribution made by female preference for conspecific pulse song towards the sexual isolation of the sibling species Drosophila melanogaster and D. simulans. Synthetic pulse songs are shown to be most effective in stimulating females when they are of conspecific mean IPI and IPI cycle length. Preferences for conspecific signals are found to be broad. In the second chapter, it is asked which element of IPI periodicity accounts for its property as a sexual stimulant in D. melanogaster. The most likely explanation, increased variation in IPI, is eliminated: female receptivity is not increased by playback of a novel synthetic song which varies to the same degree as rhythmic song but does not oscillate. In an appendix, some differences between D. sechellia and D. simulans in microsatellite loci are reported.