Étude des effets intergénérationnels d’une exposition précoce à un mélange environnemental de pesticides chez l’huître creuse, Crassostrea gigas

Anthropogenic activities release chemical substances in the environment. Those compounds enter water bodies and finally end into coastal waters that are contaminated by numerous contaminants like pesticides. The Pacific oyster, Crassostrea gigas, became a useful model in ecotoxicology, mainly because of its biological characteristics (sessile, filter feeder, external fertilization), that strongly expose it to environmental contamination. Specifically, its early-life stages are critical developmental windows highly susceptible to environmental stressors and potentially drive delayed effects later in life. Recent studies highlighted inheritance of environmentally-induced defects, arguing that DNA methylation may be a support of such phenomena. These discoveries open new perspectives in ecotoxicology, which is already facing the challenge of studying complex chemical mixtures. Therefore, two questions were addressed: (i) what are the effects of an early exposure to environmentally-relevant pesticide mixture throughout the Pacific oyster life cycle; (ii) are there intergenerational and adaptive implications of such exposure? We exposed three consecutive oyster generations to a mixture of 18 pesticides (sum concentration: 2.85 μg.L-1) during the first 48 h following fertilization. Then molecular (gene expression, DNA methylation) and phenotypic (growth, survival, swimming behaviour, metamorphosis, reproduction, etc.) endpoints were assessed throughout life cycle. Results show delayed effects in the first (F0) generation, impacting DNA methylation, metamorphosis, glycogen metabolism and on-field spat survival. Multigenerational implications were highlighted in the second (F1) generation, namely disturbance of signalling and stress response pathways at different life stages, as well as adaptive trends regarding gene expression and DNA methylation. This work is the first intergenerational study investigating the response of the Pacific oyster to environmental pesticide contamination.