ABNORMAL SPERMIOGENESIS IS ASSOCIATED WITH THE X-LINKED SEX-RATIO TRAIT IN DROSOPHILA-SIMULANS

The sex-ratio trait, known in several Drosophila species, results from X-linked meiotic drive that affects Y-bearing sperm and causes males to produce female-biased progeny. We describe spermiogenesis in three types of D, simulans males: wild-type, sex-ratio, and males that bear driver X chromosomes but do not express the sex-ratio trait because of autosomal and Y-linked suppression, Sex-ratio males show numerous spe rmatid nuclei in abnormal positions throughout their cysts, which occu rs rarely, if ever, in the two other types, The degree of the spermiog enic failure in sex-ratio males is correlated with the bias towards fe males in their progeny. This proves that: the trait is a case of meiot ic drive and strongly suggests that the abnormal spermatids are Y-bear ing ones, The number of cysts per testis, hence the production of X-be aring sperm. is not increased in sex-ratio males. Implications for the spread of the sex-ratio trait in natural populations of D. simulans a re discussed.