Sexual behavior in laboratory strains of Drosophila mercatorum that have spontaneously adopted parthenogenesis

Three instances are described in which bisexual laboratory strains spontaneously adopted an exclusively parthenogenetic mode of reproduction, even in the presence of fertile, bisexual males. The few males produced by the parthenogenetic strains lack a Y chromosome and are sterile but, nevertheless, showed no correlated impairment of normal mating behavior. In contrast, females show a strong reluctance to accept copulation. This behavioral correlate of parthenogenesis also has been observed previously in experimentally produced parthenogenetic lines. We suggest that genetic breakdown in female mating behavior may contribute to an evolutionary stimulus that results in a selective increase in the frequency of diploidizing events in unfertilized eggs. This ultimately might lead to the origin of an exclusively parthenogenetic reproductive mode.