title: Reduced adaptation of a non-recombining neo-Y chromosome.
abstract: Sex chromosomes are generally believed to have descended from a pair of homologous autosomes. Suppression of recombination between the ancestral sex chromosomes led to the genetic degeneration of the Y chromosome. In response, the X chromosome may become dosage-compensated. Most proposed mechanisms for the degeneration of Y chromosomes involve the rapid fixation of deleterious mutations on the Y. Alternatively, Y-chromosome degeneration might be a response to a slower rate of adaptive evolution, caused by its lack of recombination. Here we report patterns of DNA polymorphism and divergence at four genes located on the neo-sex chromosomes of Drosophila miranda. We show that a higher rate of protein sequence evolution of the neo-X-linked copy of Cyclin B relative to the neo-Y copy is driven by positive selection, which is consistent with the adaptive hypothesis for the evolution of the Y chromosome. In contrast, the neo-Y-linked copies of even-skipped and roundabout show an elevated rate of protein evolution relative to their neo-X homologues, probably reflecting the reduced effectiveness of selection against deleterious mutations in a non-recombining genome. Our results provide evidence for the importance of sexual recombination for increasing and maintaining the level of adaptation of a population.
authors.affiliation: Institute of Cell, Animal and Population Biology, University of Edinburgh, UK. doris.bachtrog@ed.ac.uk
authors.forename: Doris
authors.initials: D
authors.lastname: Bachtrog
authors.forename: Brian
authors.initials: B
authors.lastname: Charlesworth
mesh_terms: D000220:Adaptation, Biological; D000818:Animals; D001426:Bacterial Proteins; D019926:Cyclin B / Q000235:genetics; D004330:Drosophila / Q000235:genetics*; D029721:Drosophila Proteins / Q000235:genetics; D019143:Evolution, Molecular; D005260:Female; D017344:Genes, Insect; D018398:Homeodomain Proteins / Q000235:genetics; D008297:Male; D009419:Nerve Tissue Proteins; D011110:Polymorphism, Genetic; D011971:Receptors, Immunologic / Q000235:genetics; D011995:Recombination, Genetic; D014157:Transcription Factors / Q000235:genetics; D014998:Y Chromosome; D000097905:Roundabout Proteins
chemical_list: D001426:Bacterial Proteins; D019926:Cyclin B; D029721:Drosophila Proteins; D018398:Homeodomain Proteins; D009419:Nerve Tissue Proteins; D011971:Receptors, Immunologic; D014157:Transcription Factors; D000097905:Roundabout Proteins; C503698:CycB protein, Drosophila; C063459:En protein, Drosophila; C052837:eve protein, Drosophila