SEX-RATIO DISTORTION IN DROSOPHILA-SIMULANS - COOCCURRENCE OF A MEIOTIC DRIVE AND A SUPPRESSOR OF DRIVE

A sex-ratio distortion factor was found at high frequency in D. simula ns strains from Seychelles and New Caledonia. This factor is poorly or not expressed within those strains which are resistant to it. Its pre sence was detected by crossing females from New Caledonia or the Seych elles with males from a different geographic origin. Most of the Fl ma les obtained produced an excess of females (up to 99%) in their progen y. The two strains are infected with Wolbachia, but these micro-organi smms are not involved in the sex-ratio distortion. The sex-ratio facto r is shown to be an X-linked meiotic driver; nuclear resistance factor (s) act by suppressing the drive. It is likely that the same X-located driver invaded the two populations, which subsequently developed resi stance factor(s) against it.