Limited evidence of a genetic basis for sex determination in the common creek chub, Semotilus atromaculatus

Background/Question/Methods

Sex determination systems differ widely between fish species and can be arduous to detect, especially in taxa which lack heteromorphic sex chromosomes. The basis for sex determination is currently unknown in the common creek chub (Semotilus atromaculatus), though a genetic basis is suspected. We used 38 females and 41 males to investigate sex determination in this species, using genotyping-by-sequencing (GBS) data which contains thousands of genetic loci per individual. The software RADSex, a GWAS using GEMMA, Weir and Cockerham locus-specific FST analysis, and discriminant analysis of principal components (DAPC) were run on the GBS data to search for loci that associate with sex. Additionally, we detailed some of the challenges involved in studying sex determination in species with extremely variable mechanisms.

Results/Conclusions

While RADSex and GWAS using GEMMA failed to identify sex-associated markers, several loci showing genetic differentiation between the sexes were found by the FST analysis and DAPC. No explicit sex determination mechanism has been yet discovered in creek chub, but these loci are potential candidates for future studies. Finding a genetic determinant for sex would allow for sexing of both juvenile and adult creek chub without need for dissection, thereby facilitating research to better understand sex ratios and sex-biased behaviours, such as dispersal, in this species. Additionally, incompatible sex determination systems are thought to increase reproductive isolation, but interspecific hybridization is common among groups such as cyprinid minnows; thus, research in this area can provide insight into hybridization and evolutionary diversification of this clade.