The “cost of reproduction” is a concept defining that a high reproductive investment has a price that is paid later by an acceleration of senescence. That may translate tradeoff between reproduction and other physiological functions such as antioxidant defense. In the Pacific oyster Crassostrea gigas, reproduction is a major physiological function. In a study led to understand the summer mortalities affecting this species, a negative correlation between reproductive effort and survival was observed. Moreover, some antioxidant genes were identified as differentially expressed between lines of oysters selected for resistance or susceptibility to summer mortalities. Some studies suggest that the susceptibility to oxidative stress may represent a cost of reproduction taking part to the process of senescence. In this context, we analyzed the antioxidant capacity of oysters according to their reproductive investment. For this, the technique of RNA interference was used to manipulate the reproductive effort of oysters. The expression of the main antioxidant enzymes (transcript levels and enzyme activities) and the dosage of oxidative damages were then measured in different tissues and cells of the organism (gills, gonad, hemocytes and gametes). The results obtained in this thesis suggest that the antioxidant capacity of C. gigas is particularly effective and that reproduction alone is not sufficient to induce oxidative stress. This antioxidant capacity appears to be tissue-specific even cell-specific and glutathione metabolism would to play a major role in this protection. This resistance to oxidative stress would make C. gigas be a species particularly adapted to life in stressful environments.
