A novel sex-associated genomic region in Catostomus fish species

Genomic regions that influence sex are hypothesized to play a key role in evolutionary diversification, as sex determination mechanisms may promote or impede reproductive isolation between closely related species. Remarkably, these mechanisms are almost completely unknown in many taxa, especially in clades like fish with extremely variable sex determination. In Catostomus fishes, contemporary hybridization is extensive but variable, and factors influencing hybridization dynamics are not fully understood. We used genotyping-by-sequencing data from three Catostomus species (bluehead, white, and flannelmouth suckers) to identify regions of the genome associated with sex using a genome-wide association study. We identified a genomic region in bluehead suckers from Colorado on chromosome 4 that significantly associates with sex and is suggestive of a sex-determining region. This region is not significant in the other species studied here, or in a divergent lineage of bluehead suckers, implying that either the sex-determining region of the genome differs in these species and populations, or that technical limitations precluded identification of sex determination. These results provide the first description of sex determination systems in Catostomus species and suggest that further investigation of sex determination in the Catostomidae genus is needed to better characterize evolutionary turnover of sex determination in this species-rich group.