Different sensory modalities are required for successful courtship in two species of the Drosophila willistoni group

During courtship, specific signals are transmitted and received between the male and the female. To understand the evolution and function of courtship behaviours, these signals must be tested individually to determine their relative effects. Drosophila species have a variety of courtship patterns that use different sensory modalities, including chemosensory, tactile, visual and auditory cues, and thus provide an opportunity for exploring different sensory modalities. In most species of the Drosophila willistoni group, males produce an auditory cue (courtship song) through wing vibration. One species, Drosophila nebulosa, does not produce an auditory signal in courtship, although both sexes perform wing-lifting movements and males fan an anal droplet towards the female. We compared the sensory modalities important for mating success in D. nebulosa and D. willistoni through a series of phenotypic manipulation experiments in which individuals had disrupted transmission or reception of signals. In D. nebulosa, females had to be able to smell, presumably to detect the anal droplet, for successful mating to occur, whereas for males of the same species, vision was essential. In contrast, no single sensory modality was absolutely necessary for D. willistoni mating success, although hearing greatly increased mating success for females and courtship song greatly increased mating success for males. Thus, these species are divergent in the sensory modalities necessary for courtship success, indicating that courtship behaviour may change rapidly within species groups.