SELECTION FOR INCREASED FEMALE SEXUAL RECEPTIVITY IN RAISED STOCKS OFDROSOPHILA-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 produ ce the courtship song, which functions to increase female receptivity to copulation. As expected, rsd males are less successful when courtin g wild-type females. However, females from long-established rad stocks are more receptive to courtship stimuli and mate more readily with bo th rsd and wild-type males than do wild-type females. Genetic analysis reveals dominant factors on the X and third chromosomes that, in comb ination, are responsible for the increased receptivity of rsd females. These observations suggest that the lack of courtship song in rsd sto cks, which would be expected to reduce the vigor of the stock, may hav e functioned as a selective force, favoring mutations that increased f emale receptivity. Possible consequences of selection favoring the dev elopment of differential female receptivity on speciation are discusse d.