title: Effects of X-linkage and sex-biased gene expression on the rate of adaptive protein evolution in Drosophila.
abstract: Patterns of polymorphism and divergence in Drosophila protein-coding genes suggest that a considerable fraction of amino acid differences between species can be attributed to positive selection and that genes with sex-biased expression, that is, those expressed predominantly in one sex, have especially high rates of adaptive evolution. Previous studies, however, have been restricted to autosomal sex-biased genes and, thus, do not provide a complete picture of the evolutionary forces acting on sex-biased genes across the genome. To determine the effects of X-linkage on sex-biased gene evolution, we surveyed DNA sequence polymorphism and divergence in 45 X-linked genes, including 17 with male-biased expression, 13 with female-biased expression, and 15 with equal expression in the 2 sexes. Using both single- and multilocus tests for selection, we found evidence for adaptive evolution in both groups of sex-biased genes. The signal of adaptive evolution was particularly strong for X-linked male-biased genes. A comparison with data from 91 autosomal genes revealed a "fast-X" effect, in which the rate of adaptive evolution was greater for X-linked than for autosomal genes. This effect was strongest for male-biased genes but could be seen in the other groups as well. A genome-wide analysis of coding sequence divergence that accounted for sex-biased expression also uncovered a fast-X effect for male-biased and unbiased genes, suggesting that recessive beneficial mutations play an important role in adaptation.
authors.affiliation: Section of Evolutionary Biology, Department of Biology, University of Munich, 82152 Munich, Germany.
authors.forename: John F
authors.initials: JF
authors.lastname: Baines
authors.forename: Stanley A
authors.initials: SA
authors.lastname: Sawyer
authors.forename: Daniel L
authors.initials: DL
authors.lastname: Hartl
authors.forename: John
authors.initials: J
authors.lastname: Parsch
mesh_terms: D000220:Adaptation, Biological / Q000235:genetics*; D000818:Animals; D001483:Base Sequence; D004330:Drosophila / Q000235:genetics*; D029721:Drosophila Proteins / Q000235:genetics* / Q000378:metabolism; D019143:Evolution, Molecular; D005260:Female; D015870:Gene Expression; D050172:Genes, X-Linked / Q000235:genetics*; D008297:Male; D008969:Molecular Sequence Data; D011110:Polymorphism, Genetic; D017422:Sequence Analysis, DNA; D012737:Sex Factors
chemical_list: D029721:Drosophila Proteins