Keais, GraemeHanson, MarkGowen, BrentPerlman, Steve2017-07-312017-07-3120172017-06Keais, G.L., Hanson, M.A., Gowen, B.E., Perlman, S.J. (2017). X chromosome drive in a widespread Palearctic woodland fly, Drosophila testacea. Journal of Evolutionary Biology, 30(6), 1185-1194. doi: 10.1111/jeb.13089https://doi.org/10.1111/jeb.13089http://hdl.handle.net/1828/8385Selfish genes that bias their own transmission during meiosis can spread rapidly in populations, even if they contribute negatively to the fitness of their host. Driving X chromosomes provide a clear example of this type of selfish propagation. These chromosomes have important evolutionary and ecological consequences, and can be found in a broad range of taxa including plants, mammals and insects. Here, we report a new case of X chromosome drive (X drive) in a widespread woodland fly, Drosophila testacea. We show that males carrying the driving X (SR males) sire 80–100% female offspring and possess a diagnostic X chromosome haplotype that is perfectly associated with the sex ratio distortion phenotype. We find that the majority of sons produced by SR males are sterile and appear to lack a Y chromosome, suggesting that meiotic defects involving the Y chromosome may underlie X drive in this species. Abnormalities in sperm cysts of SR males reflect that some spermatids are failing to develop properly, confirming that drive is acting during gametogenesis. By screening wild-caught flies using progeny sex ratios and a diagnostic marker, we demonstrate that the driving X is present in wild populations at a frequency of ~ 10% and that suppressors of drive are segregating in the same population. The testacea species group appears to be a hot spot for X drive, and D. testacea is a promising model to compare driving X chromosomes in closely related species, some of which may even be younger than the chromosomes themselves.enDrosophilagenetic conflictmeiotic drivesegregation distortionselfish genetic elementsX chromosome drivePreprintDepartment of Biology