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Sex determination in the oyster Crassostrea gigas - A large longitudinal study of population sex ratios and individual sex changes

Abstract : Understanding sex determination in the Pacific oyster Crassostrea gigas, a sequential hermaphrodite, can provideprospective on the evolution of sex-determining systems for comparative reproduction from an evolutionaryperspective. Surprisingly, this mechanism is still poorly understood. To date, sex ratio and sex change have neverbeen studied at the individual level for a large size group and long-term monitoring. To this purpose, we performed an ambitious individual long-term follow-up (6 years) on a large population (cohort 1: 7488 oysters)produced from wild oysters, as well as for a second population produced from the cohort 1 (cohort 2: 4320oysters). All oysters were individually sexed from 2014 to 2019. For the cohort 1, our results showed a significantly female-biased sex ratio each year, ranging from 61 to 73% for the cohort 1. The proportion of oystersexhibiting sex change between the first two breeding seasons was 34% and decreased each year, ending at 9%between years 5 and 6. From the initial population, 1386 oysters were sexed six years in a row. Among them,58% were sequential hermaphrodites, within which 32% changed sex once (19% protandric and 13% protogynic), 19% twice, 5% three times, 1% four times and 0.1% five times. In contrast, 42% never exhibited a sexchange, within which 34% were potentially true females and 8% potentially true males. However, a logisticregression model indicates that those oysters could experience one sex reversal in subsequent years resulting thatall oysters of our population of C. gigas would be sequential hermaphrodites. Similar results were observed forthe cohort 2, although the proportion of sequential hermaphrodite was higher than the one observed for cohort1. It is supposed that a genetic basis exist for sex change in C. gigas. Our work participates to unravel the barriersexisting about the sequential hermaphroditism, the protandry and the sexual system in C. gigas, still currentlydebated.
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Submitted on : Tuesday, December 21, 2021 - 9:53:43 AM
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Coralie Broquard, Anne-Sophie Martinez, Elise Maurouard, Jean-Baptiste Lamy, Lionel Degremont. Sex determination in the oyster Crassostrea gigas - A large longitudinal study of population sex ratios and individual sex changes. Aquaculture, Elsevier, 2020, 515, pp.734555. ⟨10.1016/j.aquaculture.2019.734555⟩. ⟨hal-02559678⟩

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