title: Sex-chromosome differentiation and 'sex races' in the common frog (Rana temporaria).
abstract: Sex-chromosome differentiation was recently shown to vary among common frog populations in Fennoscandia, suggesting a trend of increased differentiation with latitude. By rearing families from two contrasted populations (respectively, from northern and southern Sweden), we show this disparity to stem from differences in sex-determination mechanisms rather than in XY-recombination patterns. Offspring from the northern population display equal sex ratios at metamorphosis, with phenotypic sexes that correlate strongly with paternal LG2 haplotypes (the sex chromosome); accordingly, Y haplotypes are markedly differentiated, with male-specific alleles and depressed diversity testifying to their smaller effective population size. In the southern population, by contrast, a majority of juveniles present ovaries at metamorphosis; only later in development do sex ratios return to equilibrium. Even at these later stages, phenotypic sexes correlate only mildly with paternal LG2 haplotypes; accordingly, there are no recognizable Y haplotypes. These distinct patterns of gonadal development fit the concept of 'sex races' proposed in the 1930s, with our two populations assigned to the 'differentiated' and 'semi-differentiated' races, respectively. Our results support the suggestion that 'sex races' differ in the genetic versus epigenetic components of sex determination. Analysing populations from the 'undifferentiated race' with high-density genetic maps should help to further test this hypothesis.
authors.affiliation: Department of Ecology and Evolution, University of Lausanne, Lausanne 1015, Switzerland nicolas.rodrigues@unil.ch.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Rodrigues
authors.affiliation: Department of Ecology and Evolution, University of Lausanne, Lausanne 1015, Switzerland.
authors.forename: Yvan
authors.initials: Y
authors.lastname: Vuille
authors.affiliation: Rana Konsult, Sjöstorp 332, Dalby 247 94, Sweden.
authors.forename: Jon
authors.initials: J
authors.lastname: Loman
authors.affiliation: Department of Ecology and Evolution, University of Lausanne, Lausanne 1015, Switzerland.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Perrin
mesh_terms: D000818:Animals; D005075:Biological Evolution; D005260:Female; D008040:Genetic Linkage; D005819:Genetic Markers; D006239:Haplotypes; D008297:Male; D011896:Rana temporaria / Q000235:genetics*; D011995:Recombination, Genetic; D012727:Sex Characteristics; D012730:Sex Chromosomes / Q000235:genetics*; D012744:Sex Ratio; D013548:Sweden
chemical_list: D005819:Genetic Markers
keywords: XY recombination; epigenetic sex determination; gonadal development; sex ratio
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