The sex determination of the oyster Crassostrea gigas : from phenotype to underlying molecular factors

• Main Author: Broquard, Coralie
• Other Authors: Biologie des Organismes et Ecosystèmes Aquatiques (BOREA), Université de Caen Normandie (UNICAEN), Normandie Université (NU)-Normandie Université (NU)-Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université des Antilles (UA), Normandie Université, Anne-Sophie Martinez
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2019
• Subjects: Sex determination; Hermaphroditism; Growth; Molecular factors; C. gigas; Déterminisme sexuel; Facteurs moléculaires; [SDV.SA]Life Sciences [q-bio]/Agricultural sciences; Crassostrea gigas
• Online Access: https://theses.hal.science/tel-03150111; https://theses.hal.science/tel-03150111/document; https://theses.hal.science/tel-03150111/file/sygal_fusion_28314-broquard-coralie.pdf

Knowledge about the mode of reproduction and the sex determination of the cupped oyster Crassostrea gigas remains limited. As a sequential hermaphroditic species, sex determination takes place several times during its lifetime. As part of this thesis, the sexual phenotypes of the first 6 years of life of oysters were identified in two cohorts. Thus, the sex ratio was biased towards females from the first sexual maturity, as well as for all subsequent years. After six years of sexing, 42%, 32%, 19%, 5%, 1% and 0.1% of oysters showed 0, 1, 2, 2, 3, 4 and 5 sex changes. The frequency of sex changes also decreased with age (34% between years 1-2 to 9% between years 5-6). This thesis work has also sought to determine the influence of sex and sex change on the morphological parameters of individuals. Thus, a sexual dimorphism was identified for the total weight as well as the length, width and thickness of the shell, in favour of female oysters, including those that have changed sex in the male to female direction. Finally, a transcriptomic analysis of the gonad of individuals with contrasted phenotypes ("true" females and "true" males) was to provide further knowledge on the molecular factors of sex determination. Thus, this approach made it possible (i) to identify the expression patterns of homologs of sex-determining genes, over the entire period of this mechanism and (ii) to identify new molecular actors of interest, overexpressed specifically in one sex during sex determination. Each expression pattern obtained in "true" males or "true" females could thus be interpreted in the light of the most probable future phenotype of the sex, despite sequential hermaphroditism. This approach allowed to refine hypotheses about the role of various factors in determining the sex of this cupped oyster. Le savoir relatif au mode de reproduction et au déterminisme sexuel de l’huître creuse Crassostrea gigas demeure limité. Etant une espèce hermaphrodite séquentielle, la détermination de son sexe a lieu plusieurs fois au cours ...