MALE EYE SPAN IN STALK-EYED FLIES INDICATES GENETIC QUALITY BY MEIOTIC DRIVE SUPPRESSION

In some species, females choose mates possessing ornaments that predic t offspring survival(1-5). However, sexual selection by female prefere nce for male genetic quality(6-8) remains controversial because conven tional genetic mechanisms maintain insufficient variation in male qual ity to account for costly preference and ornament evolution(9,10). Her e we show that females prefer ornaments that indicate genetic quality generated by transmission conflict between the sex chromosomes, By com paring sex-ratio distributions in stalk-eyed fly (Cyrtodiopsis) progen y we found that female-biased sex ratios occur in species exhibiting e ye-stalk sexual dimorphism(11,12) and female preferences for long eye span(13,14). Female-biased sex ratios result from meiotic drive(15), t he preferential transmission of a 'selfish' X-chromosome. Artificial s election for 22 generations on male eye-stalk length in sexually dimor phic C. dalmanni produced longer eye-stalks and male-biased progeny se x ratios in replicate lines. Because male-biased progeny sex ratios oc cur when a drive-resistant Y chromosome pairs with a driving X chromos ome(15), long eye span is genetically linked to meiotic drive: suppres sion. Male eye span therefore signals genetic quality by influencing t he reproductive value of offspring(16).