Restriction site-associated DNA sequencing (RAD-seq) analysis in Pacific oyster Crassostrea gigas based on observation of individual sex changes

Chenyang Yue,Hong Yu,Qi Li,Lingfeng Kong,Shikai Liu

doi:10.1038/s41598-020-67007-4

Abstract

The diverse modes of sexual reproduction in Bivalvia make it an excellent clade to understand the evolution of sex and sex determination. The cosmopolitan Pacific oyster Crassostrea gigas is an ideal model for bivalve sex determination studies because of its complicated sexuality, including dioecy, sex change and rare hermaphroditism. A major barrier to C. gigas sex determination study has been the lack of information on the type of sex determination. To identify its sex-determining system, sex observation by following the same individual in two consecutive years was conducted on 760 oysters from distinct populations. Stable sexuality and sex reversal in both directions were observed, which provides a case against the protandry of C. gigas. Restriction site-associated DNA sequencing (RAD-seq) based on 26 samples with unchanged and converted sexualities was carried out for identifying sex-linked marker. One SNP Cgsl-40 was proved to be sex-related, but sex-biased heterozygosity varied between populations for RAD-seq and validation, showing no evidence for sex chromosomes or single-locus models for C. gigas primary sex determination. Information obtained in our study provides novel insight into sex determination mechanism in C. gigas.

Highlights

Pacific oyster Crassostrea gigas based on observation of individual sex changes Chenyang Yue[1], Qi Li1,2 ✉, Hong Yu1, Shikai Liu1 & Lingfeng Kong[1]
Information obtained in our study provides novel insight into sex determination mechanism in C. gigas
In the polygenic sex determination (PGSD) system, by contrast, the sex determination genes are distributed across the genome and the combination of their alleles determines the sex of individual, in which sex behaves as a threshold quantitative trait[5,6,7]

Summary

Introduction

Pacific oyster Crassostrea gigas based on observation of individual sex changes Chenyang Yue[1], Qi Li1,2 ✉, Hong Yu1, Shikai Liu1 & Lingfeng Kong[1]. The cosmopolitan Pacific oyster Crassostrea gigas is an ideal model for bivalve sex determination studies because of its complicated sexuality, including dioecy, sex change and rare hermaphroditism. Studies in model organisms have revealed key genes and complex pathways involved in sex determination and differentiation, understanding the evolution of sex requires more information about molecular mechanisms of sex determination in diverse taxa, especially invertebrates with varying sexuality. The Bivalvia contributes the major branch of the second largest animal phylum Mollusca and diverse modes of sexual reproduction have been found, ranging from functional (simultaneous) hermaphroditism, alternative sexuality, to strict dioecy[13,14,15] This makes it an excellent clade to investigate one of most fundamental transitions in sex determination from hermaphroditism to gonochorism. Some downstream actors of the molecular cascade of the Pacific oyster sex determination, such as Cg-β-catenin, CgFoxl[2], Cg-SoxE and CgDsx, have been characterized[10,27,28,29], and several QTLs for sex were detected in linkage mapping[25,26], while no major sex-determining gene or genetic marker supporting above two genetic models has been identified

Methods

Results

Conclusion