Abnormal spermiogenesis is associated with the X-linked sex-ratio trait in Drosophila simulans

MontchampMoreau, CJ, D.,  Heredity,  79:24-30. 1997.

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 spermatid nuclei in abnormal positions throughout their cysts, which occurs rarely, if ever, in the two other types, The degree of the spermiogenic failure in sex-ratio males is correlated with the bias towards females in their progeny. This proves that: the trait is a case of meiotic drive and strongly suggests that the abnormal spermatids are Y-bearing ones, The number of cysts per testis, hence the production of X-bearing sperm. is not increased in sex-ratio males. Implications for the spread of the sex-ratio trait in natural populations of D. simulans are discussed.