Sex Markers in Two Sebastes Rockfishes

Fish have evolved a variety of sex-determining (SD) systems including male heterogamy (XX/XY), female heterogamy (ZZ/ZW), and environmental SD. Little is known about the SD mechanisms of Sebastes rockfishes, a group of importance to sport and commercial fishing. This study aims to identify genetic sex markers in the sympatrically distributed sister species S. chrysomelas (black-and-yellow rockfish) and S. carnatus (gopher rockfish). Sex-specific loci are present only in the heterogametic sex and would allow for genetic sexing with PCR and gel electrophoresis, a beneficial method because males and females are not readily identified based on external morphology. Ability to sex individuals genetically would aid in population, aquaculture, and toxicological studies in the genus. To identify markers, the program Stacks was used to assemble a catalog of over 1.47 million loci from double digest restriction site –associated DNA sequencing (ddRAD-seq) of 40 individuals. Loci were filtered for presence in all of the individuals of one sex, no presence in the other sex, and no heterozygous single nucleotide polymorphisms (SNPs). A total of 33 male-specific loci met the criteria in at least one species. Both species appear to exhibit male heterogamy. Sex-specific loci were interspersed between loci that were not divergent between sexes, and mapped to a 5 Mbp section of a single chromosome in a reference species. We identified potential genes involved in SD, including transcription factors, activators, and epigenetic regulators. Putative sex-specific loci will be validated with PCR and gel electrophoresis of additional sexed samples.