title: Faster-X effects in two Drosophila lineages.
abstract: Under certain circumstances, X-linked loci are expected to experience more adaptive substitutions than similar autosomal loci. To look for evidence of faster-X evolution, we analyzed the evolutionary rates of coding sequences in two sets of Drosophila species, the melanogaster and pseudoobscura clades, using whole-genome sequences. One of these, the pseudoobscura clade, contains a centric fusion between the ancestral X chromosome and the autosomal arm homologous to 3L in D. melanogaster. This offers an opportunity to study the same loci in both an X-linked and an autosomal context, and to compare these loci with those that are only X-linked or only autosomal. We therefore investigated these clades for evidence of faster-X evolution with respect to nonsynonymous substitutions, finding mixed results. Overall, there was consistent evidence for a faster-X effect in the melanogaster clade, but not in the pseudoobscura clade, except for the comparison between D. pseudoobscura and its close relative, Drosophila persimilis. An analysis of polymorphism data on a set of genes from D. pseudoobscura that evolve rapidly with respect to their protein sequences revealed no evidence for a faster-X effect with respect to adaptive protein sequence evolution; their rapid evolution is instead largely attributable to lower selective constraints. Faster-X evolution in the melanogaster clade was not related to male-biased gene expression; surprisingly, however, female-biased genes showed evidence for faster-X effects, perhaps due to their sexually antagonistic effects in males.
authors.affiliation: Institute of Evolutionary Biology, University of Edinburgh, United Kingdom Present address: Institute of Biological, Environmental and Rural Sciences, Abertystwyth University, Aberystwyth, United Kingdom.
authors.forename: Victoria
authors.initials: V
authors.lastname: Avila
authors.affiliation: Institute of Evolutionary Biology, University of Edinburgh, United Kingdom Present address: MRC Human Genetics Unit, MRC IGMM, University of Edinburgh, Edinburgh, United Kingdom.
authors.forename: Sophie
authors.initials: S
authors.lastname: Marion de Procé
authors.affiliation: Institute of Evolutionary Biology, University of Edinburgh, United Kingdom.
authors.forename: José L
authors.initials: JL
authors.lastname: Campos
authors.affiliation: Institute of Evolutionary Biology, University of Edinburgh, United Kingdom.
authors.forename: Helen
authors.initials: H
authors.lastname: Borthwick
authors.affiliation: Institute of Evolutionary Biology, University of Edinburgh, United Kingdom.
authors.forename: Brian
authors.initials: B
authors.lastname: Charlesworth
authors.affiliation: Institute of Evolutionary Biology, University of Edinburgh, United Kingdom Present address: Institut for Populationsgenetik, Vetmeduni Vienna, Vienna, Austria andrea.betancourt@vetmeduni.ac.at.
authors.forename: Andrea J
authors.initials: AJ
authors.lastname: Betancourt
mesh_terms: D000818:Animals; D002875:Chromosomes / Q000235:genetics; D004330:Drosophila / Q000235:genetics; D004331:Drosophila melanogaster / Q000235:genetics*; D012641:Selection, Genetic / Q000235:genetics
keywords: Drosophila melanogaster; Drosophila pseudoobscura; faster-X effect; positive selection; sex-biased gene expression