SELECTION FOR INCREASED FEMALE SEXUAL RECEPTIVITY IN RAISED STOCKS OF DROSOPHILA-MELANOGASTER

Two third-chromosome mutations in raised (rsd) stocks, when homozygous, cause the wings of Drosophila melanogaster adults to be held upright. Males expressing these mutations cannot vibrate their wings to produce the courtship song, which functions to increase female receptivity to copulation. As expected, rsd males are less successful when courting wild-type females. However, females from long-established rad stocks are more receptive to courtship stimuli and mate more readily with both rsd and wild-type males than do wild-type females. Genetic analysis reveals dominant factors on the X and third chromosomes that, in combination, are responsible for the increased receptivity of rsd females. These observations suggest that the lack of courtship song in rsd stocks, which would be expected to reduce the vigor of the stock, may have functioned as a selective force, favoring mutations that increased female receptivity. Possible consequences of selection favoring the development of differential female receptivity on speciation are discussed.