No abstract

International audienceSize is the most important and valuable quality of the cultured black-lip pearl, Pinctada margaritifera. As this pearl aquaculture is carried out at numerous grow-out sites, this study analyzes the environmental influence on pearl size parameters (nacre weight and thickness) in relation to the recipient oyster biometric parameters (shell thickness, height, width, and oyster weight) at harvest time. Toward this end, an experimental graft was designed by using a homogeneous donor oyster phenotype. The recipient oysters were randomly and equally transferred and reared in five commercial and contrasting grow-out locations. Overall inter-site comparisons revealed that the cultured pearl size (N = 2168) and the biometric parameters of the recipient oysters were highest for sites with warmer temperatures with low seasonal variation in comparison to the southern latitude sites. These results were supported by positive correlations between pearl nacre thickness and recipient oyster shell thickness, height, and width. In parallel, the biomineralization potential of the mantle graft was screened through four genes encoding aragonite (Pif 177, MSI60) and calcite (shematrin 9, aspein). As the gene expression levels were the same among all the donor oysters, this finding demonstrates that: 1) the pearl sac that originated from the mantle graft was not isolated from environmental variations during the culture period and 2) the phenotypic expressions of the two biomineralizing tissues in the recipient oyster were consistent (shell and pearl). In the near future, this knowledge will be helpful at the production sites of genetically selected donor oyster lines for growth produced in hatchery systems. Culture site dependence on pearl size realization in Pinctada margaritifera in relation to recipient oyster growth and mantle graft biomineralization gene expression using the same donor phenotype. Available from: https://www.researchgate.net/publication/299384948_Culture_site_dependence_on_pearl_size_realization_in_Pinctada_margaritifera_in_relation_to_recipient_oyster_growth_and_mantle_graft_biomineralization_gene_expression_using_the_same_donor_phenotype [accessed Oct 18 2017]

SummaryPinctada margaritifera is French Polynesia's most economically important aquaculture species. This pearl oyster has the specific ability to produce cultured pearls with a very wide range of colours, depending on the colour phenotypes of donor oysters used. Its aquaculture is still based on natural spat collection from wild stocks. We investigated three rare colour variants of P. margaritifera -orange flesh, and red and white shell colour phenotypes -in comparison with the wild-type black flesh and shell commonly found in this species. The study aimed to assess the geographic distribution and genetic basis of these colour variants. Colour frequencies were evaluated during transfer and graft processes of pearl oyster seed captured at collector stations. Among the collection locations studied, Mangareva Island showed the highest rate of the orange flesh phenotype, whereas Takaroa and Takume atolls had relatively high rates of red and white shell phenotypes respectively. Broodstocks were made of these rare colour variants, and crosses were performed to produce first-and secondgeneration progenies to investigate segregation. The results were consistent with Mendelian ratios and suggest a distinct model with no co-dominance: (i) a two-allele model for flesh trait, whereby the orange allele is recessive to the black fleshed type, and (ii) a three-allele model for shell trait, whereby the black wild-type allele is dominant to the red coloration, which is dominant to the white shell. Furthermore, the proposed model provides the basis for producing selected donor pearl oyster lines through hatchery propagation.