Abstract
Simple SummaryBivalve sex is thought to fluctuate depending on environmental conditions. So far, there has been no investigation on the phenotypic stability of sex in the commercially important Yesso scallop Mizuhopecten yessoensis. The present study revealed that the sex of the Yesso scallop is stable after initial sex differentiation and that this species maintains a sex-stable maturation system throughout its life. In addition, gonad differentiation for each sex was precisely characterized by using molecular markers throughout the maturational cycle.The objective of the present study was to analyze the phenotypic stability of sex after sex differentiation in the Yesso scallop, which is a gonochoristic species that has been described as protandrous. So far, no study has investigated in detail the sexual fate of the scallop after completion of sex differentiation, although bivalve species often show annual sex change. In the present study, we performed a tracking experiment to analyze the phenotypic stability of sex in scallops between one and two years of age. We also conducted molecular marker analyses to describe sex differentiation and gonad development. The results of the tracking experiment revealed that all scallops maintained their initial sex phenotype, as identified in the last reproductive period. Using molecular analyses, we characterized my-dmrt2 and my-foxl2 as sex identification markers for the testis and ovary, respectively. We conclude by proposing that the Yesso scallop is a sex-stable bivalve after its initial sex differentiation and that it maintains a sex-stable maturation system throughout its life. The sex-specific molecular markers identified in this study are useful tools to assess the reproductive status of the Yesso scallop.
Highlights
Systems of sex differentiation and phenotypic stability of sex have evolved into diverse forms in molluskan species and often show species-specific features
We set up two rearing ropes for each sexed scallop population and performed additional rearing until the reproductive season to confirm their subsequent sex phenotype (Figure 1I)
The present study focused on the phenotypic stability of sex in the adult Yesso scallop after sex differentiation, suggesting that this scallop is a sex-stable bivalve after sex differentiation and maintains a sex-stable maturation system throughout its life
Summary
Systems of sex differentiation and phenotypic stability of sex have evolved into diverse forms in molluskan species and often show species-specific features. Owing to the diversity of sex-controlling systems, there is still controversy about the molecular mechanisms of sex differentiation, in bivalves. Previous studies [2,3,4,5] have proposed that all juveniles first differentiate into males possessing a small amount of sperm, and in the reproductive season, some of the males undergo a sex change to female via a hermaphroditic transition phase. The sex differentiation of the Yesso scallop is generally completed within one year in most parts of Japan where aquaculture of this species is performed [5].
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