Les bénitiers font partie des espèces protégées, mais l’espèce Tridacna maxima reste encore très présente en Polynésie française. L’étude de sa structure génétique a permis de caractériser pour la première fois une lignée monophylétique de bénitiers en Polynésie Française, composée de deux clades distincts répartis de part et d’autre d’un axe nord-ouest/sud-est séparant majoritairement les populations des Tuamotu (mapiko nord) de celles des autres archipels (mapiko sud). La connectivité entre les populations des différentes îles n’est pas cohérente avec les courants océaniques de surface actuels en Polynésie française. Ces résultats, et ceux obtenus sur des bénitiers provenant de Fidji et de Tonga, ont permis d’émettre des hypothèses sur la colonisation de la Polynésie française par les bénitiers et les facteurs qui ont influencé la connectivité actuelle. Présentant une plus faible diversité génétique que les populations de T. maxima de la région Indo-Pacifique, celles de Polynésie française pourraient être plus vulnérables aux changements environnementaux. La capacité d’adaptation au stress des bénitiers a été étudiée par une étude intégrée des variations de la composition en métabolites et de l’expression génique lors d’expériences de réchauffement. La composition en acides gras des bénitiers a notamment été établie pour la première fois lors de nos travaux, et sa variation évaluée au cours du stress. Les données de transcriptomiques ont pour la première fois mise à jour les voies de réponses au stress thermique chez les bénitiers dont certaines semblent corrélées aux variations observées de la composition en acide gras. L’effet de la proximité des bénitiers avec les coraux dans le milieu et l’impact d’un second type de stress supplémentaire ont également été évalués. L’étude des Symbiodinium des bénitiers a permis de montrer que leur résistance et leur capacité d’adaptation au stress d’une durée de 15 jours seraient indépendantes des communautés symbiotiques. Mots clé : Tridacna maxima, bénitier, Polynésie française, diversité génétique, stress thermique, étude intégrée, transcriptomique, métabolomique, Symbiodinium. / Giant clams are endangered species but Tridacna maxima is still well represented in French Polynesia. Firstly, the genetic structure assessment has led to the discovery of a monophyletic group composed of two new T. maxima clades in French Polynesia which cohabite over a large area with a North-West South-East axis on either side of which, one of each clade is dominant: “North Mapiko” (Tuamotu group) and “South Mapiko” (other archipelagos group). Interconnectivity between different island giant clam populations is not consistent with the present flow of oceanic currents. These results, along with those obtained for Tongian and Fidjian samples, allowed us to suggest hypothesis regarding the giant clam colonization of French Polynesia and the factors which may have influenced the present connectivity. French Polynesian T. maxima was found to have a lower genetic diversity compared to those from Indo-Pacific region, and so considered to be relatively more vulnerable to environmental global changes. Stress adaptation capacity of giant clam was assessed by the follow-up of the metabolite composition and gene expression variations during a thermal time course experiment. Giant clam fatty acid composition was established for the first time and its variation was evaluated along the stress experiment. Impact of the thermal stress on the metabolite composition and gene expression were disclosed. Variation in fatty acids compositions was observed and linked to variation in some specific gene expression. Impact of giant clam proximity with corals and impact of a second supplementary applied stress were also assessed. Study of Symbiodinium symbiosis with giant clam showed that giant clam resistance and adaptation capacity observed for 15 days was independent of symbiotic community behavior. Key words : Tridacna maxima, giant clam, French Polynesia, genetic diversity, thermal stress, integrative approach, transcriptomic, metabolomic, Symbiodinium.

Giant clams (Tridacnidae) are economic species which have been the main materials for ganbei. Due to a huge decline in population size, it was reported as an endangered species in CITES list. In this study, the effects of different preservative methods on the expression of DNA sequences in giant clams were examined and whether ganbai is made from giant clams were also determined. I collected samples from Kenting, Green Island, Orchid Island, Shaio-Liu-Chu and Penghu Islands. And, ganbei were bought from markets. Species identification was based on four DNA sequences (COI, 16S, 18S, 28S) and morphological characters. The distinction power of four preservative methods (-70 ¢J frozen, 70 % ethanol, dried and freeze dried) on clam samples was evaluated. DNA sequences of CO1 and 16S are the best fragments to distinguish samples at species level. Additionally, a cryptic species of Tridacna noae was found from Tridacna maxima. The 18S and 28S sequences have low variation among giant clam species which are more suitable for higher level of phylogeny. The DNA fragments with different preservative methods were mostly in good condition having extracted DNA size up to 10 Kb. The sequencing divergences of the four preservation were 0 - 0.020 within an individual and 0 - 0.070 among individuals. In conclusion, the four preservative methods are similar in sequence expression. Ganbei made from giant clams was not found in the market. Instead, commercial ganbei are made from scallops, mostly Patinopecten yessoensis and some Argopecten irradians.

Thesis (M.E.S.)--The Evergreen State College, 2008. / Title from title screen (viewed 10/21/2009). Includes bibliographical references (leaves 62-72).