Behavioural pleiotropy of theyellowgene inDrosophila melanogaster

SUMMARY Theyellowmutant (y− 1:0·0) ofDrosophila melanogastershows a reduction in body pigmentation associated with a decrement in locomotor activity and in male competitive mating ability. The effects of the mutant gene are specific to locomotor activity in the adult fly, measures of larval activity being unaffected. In the presence of active femalesyellowmales offer a reduced intensity of sexual stimulation because they are less able to maintain contact during courtship. However, the impaired locomotor performance ofyellowmales is not the general cause for their reduced competitive mating ability, since the stimuli provided byyellowmutants courting inactive females appear to be both quantitatively and qualitatively indistinguishable from those of their wild-type male sibs. Nor is there any good evidence, as measured by the frequency of rejection responses, that the courtship stimulation offered by theyellowmales is less acceptable to the females. The mutant males are nevertheless unsuccessful in achieving copulation with such females. It is suggested that impairment of mating ability inyellowmales may be caused by changes in the efficiency for mating of their secondary sexual structures due to the effect of theyellowgene on the properties of the cuticle.