One of the main issues in ecotoxicology nowadays is understanding the effects of exposure to pollutant low concentrations on organisms' vulnerable life stages, life history, as well as their multi- and transgenerational effects. Early life stages are crucial for development and can be disrupted by environmental factors such as xenobiotics, nutrition and physico-chemical changes, affecting the subsequent life history and survival. Recent works highlight the role of epigenetic alterations in mediating the response to environmental toxicant exposure. Epigenetic-driven mechanisms are fundamental during embryo development as they coordinate the precise expression of key genes in space and time. Indeed, pollutant-mediated dysregulation of embryo epigenomes has potential implications in subsequent developmental disorders, over the life course or over generations.

Aquatic environments are the ultimate receptacles for many anthropogenic chemicals, to which species with external fertilization expose vulnerable stages, such as gametes, embryos and larvae. Oysters Crassostrea gigas are considered bioindicators of water quality and a model species for marine ecotoxicology studies due to their ecological characteristics (benthic, sessile, external fertilization). Recent studies on this model demonstrate the negative effects of parental exposure to several pollutants on offspring, including in the case of a specific pesticide exposure, global and specific DNA methylation variations in the progeny. While the impact of pollutants on the progeny epigenome suggests a multigenerational effect, direct effects on gamete methylation was also observed. More recently, oyster embryo development was shown to depend on DNA methylome dynamics, and larval abnormalities have been linked to DNA methylation changes during early-development. Therefore the next step would be to explore the relationship between chemical-driven perturbations in embryos and effects on life history as well as on progeny.

The main goal of the PESTO project is to investigate the effects of a low-concentration mixture of pesticides on larval development, life history (larval recruitment, growth, reproduction), and multi- and trans-generational traits in oysters. Three main questions will be addressed:

(i) which are the effects of an early exposure to a pollutant mixture on the life history of an organism (development, larval recruitment, growth and reproduction)? (ii) Which are the transcriptomic and epigenetic pathways underlying these effects?

(iii) Are these effects persistent in the offspring of exposed animals? Can acclimatization be observed in the offspring of exposed organisms if they are in turn exposed to the same stress? To answer these questions a combined approach at molecular (transcriptomic and epigenetic) and organism-scale (larval recruitment, growth, reproduction) will be developed.

The novelty of this study lies in the proposed experimental plan which will cover the entire oyster life cycle, from the F0 embryo development to the F1 and F2 offspring, considering multigenerational effects of exposure to a mixture of pollutants which will better reflect the environment. The PESTO project will provide new knowledge to explain pesticide toxicity at a multi- and trans-generational scale, giving insights into molecular mechanisms related either to acclimatization or weakening effects through combined transcriptomic and epigenetic approaches.