title: Dmrt1 polymorphism covaries with sex-determination patterns in Rana temporaria.
abstract: Patterns of sex-chromosome differentiation and gonadal development have been shown to vary among populations of Rana temporaria along a latitudinal transect in Sweden. Frogs from the northern-boreal population of Ammarnäs displayed well-differentiated X and Y haplotypes, early gonadal differentiation, and a perfect match between phenotypic and genotypic sex. In contrast, no differentiated Y haplotypes could be detected in the southern population of Tvedöra, where juveniles furthermore showed delayed gonadal differentiation. Here, we show that Dmrt1, a gene that plays a key role in sex determination and sexual development across all metazoans, displays significant sex differentiation in Tvedöra, with a Y-specific haplotype distinct from Ammarnäs. The differential segment is not only much shorter in Tvedöra than in Ammarnäs, it is also less differentiated and associates with both delayed gonadal differentiation and imperfect match between phenotypic and genotypic sex. Whereas Tvedöra juveniles with a local Y haplotype tend to ultimately develop as males, those without it may nevertheless become functional XX males, but with strongly female-biased progeny. Our findings suggest that the variance in patterns of sex determination documented in common frogs might result from a genetic polymorphism within a small genomic region that contains Dmrt1. They also substantiate the view that recurrent convergences of sex determination toward a limited set of chromosome pairs may result from the co-option of small genomic regions that harbor key genes from the sex-determination pathway.
authors.affiliation: Department of Ecology and Evolution University of Lausanne CH 1015 Lausanne Switzerland.
authors.forename: Wen-Juan
authors.initials: WJ
authors.lastname: Ma
authors.affiliation: Department of Ecology and Evolution University of Lausanne CH 1015 Lausanne Switzerland.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Rodrigues
authors.affiliation: Department of Ecology and Evolution University of Lausanne CH 1015 Lausanne Switzerland.
authors.forename: Roberto
authors.initials: R
authors.lastname: Sermier
authors.affiliation: Department of Ecology and Evolution University of Lausanne CH 1015 Lausanne Switzerland; Present address: Department of Biology University of California at Riverside California 92521.
authors.forename: Alan
authors.initials: A
authors.lastname: Brelsford
authors.affiliation: Department of Ecology and Evolution University of Lausanne CH 1015 Lausanne Switzerland.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Perrin
keywords: Gonadal development; homomorphic sex chromosomes; nonrecombining segment; sex determination; sex races; sex reversal