Genetic diversity and signatures of selection in the mito-gynogenetic olive flounder Paralichthys olivaceus revealed by genome-wide SNP markers

The artificial gynogenesis technique has been proven to be an effective genetic tool and has been widely used in fish breeding. The evaluation of the genetic basis of the artificial gynogenetic population is essential for breeding and farming, and the detection of the signatures of selection is potential to elucidate genes and mutations associated with important phenotypic traits. Olive flounder Paralichthys olivaceus is a commercially important flatfish species cultured in China, Japan, and Korea, and artificial gynogenesis has been used for its genetic breeding. In this study, the genetic variation of the artificial mito-gynogenetic population and common population of the flounder were analyzed using SNP markers with 2b-RAD genotyping technique. A total of 162 mito-gynogenetic and 90 common flounders were used, and 39,018 high-quality genome-wide single nucleotide polymorphisms (SNPs) were identified across two populations. The average observed heterozygosity (Ho) and average expected heterozygosity (He) of SNP were 0.1895 and 0.2413, and 0.0222 and 0.2974 in the common and mito-gynogenetic populations, respectively. Most loci significantly deviated from Hardy-Weinberg equilibrium (HWE) after Bonferroni correction in the former population. However, the genetic distance between the two populations suggested no significant genetic differentiation. Furthermore, analysis of run of homozygosity (ROH) showed low level of genomic inbreeding in the common population (inbreed coefficient was 0.2171) compared to higher inbreeding in the mito-gynogenetic population (inbreed coefficient was 0.9227). Short ROHs were more frequent in the common population, while long ROHs were more frequent in the mito-gynogenetic population, providing insight in the developmental history of the flounder. A total of 580 genes with putative selection signatures were identified across the two populations based on selective sweeps. These genes were involved in 39 KEGG pathways associated with some important traits, such as reproduction (e.g., sox8 and sox9) and immune response (e.g., dctn5 and socs-1). These results would be helpful for molecular marker-assisted breeding and conservation of genetic resources in the olive flounder and other marine culture fish.