||Boudry Pierre, Degremont Lionel, Bedier Edouard, Pouvreau Stephane, Normand Julien, Ernande Bruno
||International Workshop "Physiological aspects of reproduction and nutrition in Mollusks"
||Selective breeding, Reproduction, Genetic variation, Crassostrea gigas, Pacific oyster, Genetic
||To date, the most significant method to genetically reduce reproductive effort in the Pacific oyster (Crassostrea gigas) has been through the production of triploids, especially since the development of tetraploid lines allowing the breeding of 'natural' triploids. Gametogenesis of triploid oysters is strongly reduced compared with diploids, although they are not fully sterile and can produce viable gametes and some progenies when crossed with diploids. Reduced reproductive allocation and higher heterozygocity are commonly proposed as the main reasons why triploids often present superior yield compared with diploids. Temperature and food availability are known to favour gametogenesis in triploids, but the existence of genetic variation for this trait remains to be investigated. In diploid oysters, quantitative genetics studies suggest that significant genetic variation exists for reproductive effort and its plasticity. When food abundance increases, resource allocation was found to shift from survival to growth and reproductive effort. Reproductive effort plasticity and mean survival were highly heritable, whereas for growth, both mean and plasticity had low heritability. The genetic correlations between reproductive effort and both survival and growth were negative when food availability was low, suggesting trade-offs, but positive when food availability was high. We found positive genetic correlations between reproductive effort plasticity and both growth and survival means. When selecting for high ('R') or low ('S') survival of seed during the first summer in three oyster production sites in France, we confirmed the high heritability of this trait and observed differences in reproductive allocation. Interestingly, this correlated response varied between sites and/or experimentally controlled conditions, confirming the plasticity of the correlation between reproductive allocation and survival. Hypothesis explaining how additive genetic variance for fitness-related traits appears to be maintained in wild populations and potential consequences of our findings for selective breeding of diploid and polyploid oysters will be discussed.