Draft genome assemblies and population genomic data in multiple species of Siluridae

Sex determining genes and sex chromosomes are studied in species scattered across the tree of life, yet little is known about tempo and mode of their evolution among closely related species. Here, based on three new chromosome-scale assemblies in Silurus microdorsalis, S. glanis and S. lanzhouensis along with our previous assemblies of S. meridionalis and S. asotus, we traced the evolution of sex chromosome in a teleost order (Silurus) following the fate of a known sex-determining (SD) gene amhr2y. Our results revealed an XY system of sex determination on Chr24 (the right arm) of S. microdorsalis, Chr24 (the left arm) of S. glanis, S. lanzhouensis, S. meridionalis and Chr5 of S. asotus. The five species share partially syntenic male-specific region on chromosome Y (MSY) that contains a common SD gene amhr2y, although the whole lengths of MSY in each species are different (from 320 to 550 kb). Analyses of synteny, phylogeny and transposable elements revealed that amhr2y might be originated by an interchromosomal transposition driven by LTR/Gpysy class I element with a copy-and-paste process from Chr8 to Chr24 (the right arm) in the ancestor of Silurus. In the latter, translocation of amhr2y from the right arm to the left arm of Chr24 in the ancestor of S. glanis, S. asotus, S. lanzhouensis and S. meridionalis and from the left arm of Chr24 to Chr5 in the ancestor of S. asotus might be mediated by DNA/hAT transposons with the cut-and-paste mode. Taken together, shift in sex chromosomes but conservation of the SD gene characterized in a clade of vertebrates (Silurus) provides new examples for deep understanding of fish sex determination.