Evolution of Genetic Sex Determination in Fish

Fish show a great variety of sex determination mechanisms, which in the case of genetic sex determination is linked to a similarly high variability of sex chromosome differentiation. But this diversity does not follow any obvious phylogenetic pattern. To obtain a better understanding of the biological meaning of the diversity of sex determination and the mechanisms driving sex chromosome evolution we are attempting to decipher the molecular basis of the primary sex determination mechanisms and the structure and genetic organization of sex chromosomes across a broad diversity of rayfin fish. On the one hand we are analyzing a broad collection of species that represent major branches of the fish tree of life and on the other hand we focus on closely related species within branches of the phylogenetic tree (Salmoniformes, Esociformes, Danios, Poeciliids). We use high throughput marker mapping in 40 species as well as transcriptomics and genome sequencing to delineate sex-specific chromosomal regions and to identify candidate sex determining genes. These strategies already led to the identification of sex-specific markers, allowing delineating the extent of recombination suppression, and candidate sex determining genes in some species. Examples taken from Salmoniformes and its sister taxonomical clade i.e, the Esociformes will be described.