title: Sex-ratio meiotic drive and Y-linked resistance in Drosophila affinis.
abstract: Genetic elements that cheat Mendelian segregation by biasing transmission in their favor gain a significant fitness benefit. Several examples of sex-ratio meiotic drive, where one sex chromosome biases its own transmission at the cost of the opposite sex chromosome, exist in animals and plants. While the distorting sex chromosome gains a significant advantage by biasing sex ratio, the autosomes, and especially the opposite sex chromosome, experience strong selection to resist this transmission bias. In most well-studied sex-ratio meiotic drive systems, autosomal and/or Y-linked resistance has been identified. We specifically surveyed for Y-linked resistance to sex-ratio meiotic drive in Drosophila affinis by scoring the sex ratio of offspring sired by males with a driving X and one of several Y chromosomes. Two distinct types of resistance were identified: a restoration to 50/50 sex ratios and a complete reversal of sex ratio to all sons. We confirmed that fathers siring all sons lacked a Y chromosome, consistent with previously published work. Considerable variation in Y-chromosome morphology exists in D. affinis, but we showed that morphology does not appear to be associated with resistance to sex-ratio meiotic drive. We then used two X chromosomes (driving and standard) and three Y chromosomes (susceptible, resistant, and lacking) to examine fertility effects of all possible combinations. We find that both the driving X and resistant and lacking Y have significant fertility defects manifested in microscopic examination of testes and a 48-hr sperm depletion assay. Maintenance of variation in this sex-ratio meiotic drive system, including both the X-linked distorter and the Y-resistant effects, appear to be mediated by a complex interaction between fertility fitness and transmission dynamics.
authors.affiliation: Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853 unckless@cornell.edu.
authors.forename: Robert L
authors.identifier: http://orcid.org/0000-0001-8586-7137
authors.initials: RL
authors.lastname: Unckless
authors.affiliation: Department of Biology, University of Rochester, Rochester, New York 14627.
authors.forename: Amanda M
authors.initials: AM
authors.lastname: Larracuente
authors.affiliation: Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853.
authors.forename: Andrew G
authors.initials: AG
authors.lastname: Clark
mesh_terms: D000818:Animals; D020090:Chromosome Segregation; D004330:Drosophila / Q000235:genetics*; D005260:Female; D008297:Male; D008540:Meiosis / Q000235:genetics*; D012744:Sex Ratio; D014960:X Chromosome; D014998:Y Chromosome
keywords: Drosophila affinis; genetic conflict; genetics of sex; sex chromosomes; sex-ratio meiotic drive