Contrasting patterns of X-chromosome divergence underlie multiple sex-ratio polymorphisms in stalk-eyed flies

Sex-linked segregation distorters cause offspring sex ratios to differ from equality. Theory predicts that such selfish alleles may either go to fixation and cause extinction, reach a stable polymorphism, or initiate an evolutionary arms race with genetic modifiers. The extent to which a sex ratio distorter follows any of these trajectories in nature is poorly known. Here we used X-linked sequence and simple tandem repeat data for three sympatric species of stalk-eyed flies (Teleopsis whitei and two cryptic species of T. dalmanni) to infer the evolution of distorting X chromosomes. By screening large numbers of field and recently lab-bred flies we found no evidence of males with strongly female-biased sex ratio phenotypes (SR) in one species but high frequencies of SR males in the other two species. In the two species with SR males, we find contrasting patterns of X chromosome evolution. T. dalmanni - 1 shows chromosome-wide differences between sex-ratio (XSR) and standard (XST) X ch...