title: Sex-Chromosome Homomorphy in Palearctic Tree Frogs Results from Both Turnovers and X-Y Recombination.
abstract: Contrasting with birds and mammals, poikilothermic vertebrates often have homomorphic sex chromosomes, possibly resulting from high rates of sex-chromosome turnovers and/or occasional X-Y recombination. Strong support for the latter mechanism was provided by four species of European tree frogs, which inherited from a common ancestor (∼ 5 Ma) the same pair of homomorphic sex chromosomes (linkage group 1, LG1), harboring the candidate sex-determining gene Dmrt1. Here, we test sex linkage of LG1 across six additional species of the Eurasian Hyla radiation with divergence times ranging from 6 to 40 Ma. LG1 turns out to be sex linked in six of nine resolved cases. Mapping the patterns of sex linkage to the Hyla phylogeny reveals several transitions in sex-determination systems within the last 10 My, including one switch in heterogamety. Phylogenetic trees of DNA sequences along LG1 are consistent with occasional X-Y recombination in all species where LG1 is sex linked. These patterns argue against one of the main potential causes for turnovers, namely the accumulation of deleterious mutations on nonrecombining chromosomes. Sibship analyses show that LG1 recombination is strongly reduced in males from most species investigated, including some in which it is autosomal. Intrinsically low male recombination might facilitate the evolution of male heterogamety, and the presence of important genes from the sex-determination cascade might predispose LG1 to become a sex chromosome.
authors.affiliation: Department of Ecology & Evolution, Biophore Building, University of Lausanne, Lausanne, Switzerland christophe.dufresnes@unil.ch.
authors.forename: Christophe
authors.initials: C
authors.lastname: Dufresnes
authors.affiliation: Laboratory of Behavioral and Population Ecology, School of Biological Sciences, Seoul National University, Seoul, Republic of Korea.
authors.forename: Amaël
authors.initials: A
authors.lastname: Borzée
authors.affiliation: Department of Ecology & Evolution, Biophore Building, University of Lausanne, Lausanne, Switzerland.
authors.forename: Agnès
authors.initials: A
authors.lastname: Horn
authors.affiliation: Leibniz-Institute of Freshwater Ecology and Inland Fisheries-IGB, Berlin, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Stöck
authors.affiliation: Department of Ecology & Evolution, Biophore Building, University of Lausanne, Lausanne, Switzerland.
authors.forename: Massimo
authors.initials: M
authors.lastname: Ostini
authors.affiliation: Department of Ecology & Evolution, Biophore Building, University of Lausanne, Lausanne, Switzerland.
authors.forename: Roberto
authors.initials: R
authors.lastname: Sermier
authors.affiliation: Department of Ecology & Evolution, Biophore Building, University of Lausanne, Lausanne, Switzerland.
authors.forename: Jérôme
authors.initials: J
authors.lastname: Wassef
authors.affiliation: Institute of Cytology, Russian Academy of Sciences, St. Petersburg, Russia.
authors.forename: Spartak N
authors.initials: SN
authors.lastname: Litvinchuck
authors.affiliation: Laboratory of Behavioral and Population Ecology, School of Biological Sciences, Seoul National University, Seoul, Republic of Korea.
authors.forename: Tiffany A
authors.initials: TA
authors.lastname: Kosch
authors.affiliation: Laboratory of Behavioral and Population Ecology, School of Biological Sciences, Seoul National University, Seoul, Republic of Korea.
authors.forename: Bruce
authors.initials: B
authors.lastname: Waldman
authors.affiliation: Department of Life Sciences and Division of EcoScience, Ewha Womans University, Seoul, Republic of Korea.
authors.forename: Yikweon
authors.initials: Y
authors.lastname: Jang
authors.affiliation: Department of Ecology & Evolution, Biophore Building, University of Lausanne, Lausanne, Switzerland.
authors.forename: Alan
authors.initials: A
authors.lastname: Brelsford
authors.affiliation: Department of Ecology & Evolution, Biophore Building, University of Lausanne, Lausanne, Switzerland.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Perrin
mesh_terms: D000483:Alleles; D000818:Animals; D001001:Anura / Q000235:genetics*; D019143:Evolution, Molecular; D005260:Female; D008040:Genetic Linkage; D049810:Genetic Speciation; D008297:Male; D018895:Microsatellite Repeats; D010802:Phylogeny; D011995:Recombination, Genetic; D014960:X Chromosome / Q000235:genetics*; D014998:Y Chromosome / Q000235:genetics*
keywords: DMRT1; Hyla; fountain of youth hypothesis; recombination; sex-chromosome transitions