Résumé
Inducible defences in response to predation risk are a well-known example of adaptive phenotypic plasticity. Although inducibledefences have been studied mainly within a generation (within-generational plasticity), there is now clear evidence that ancestralexposure to predation risk can in uence the defences expressed by offspring, even if they have not been exposed themselves(transgenerational plasticity). The molecular mechanisms allowing the transmission of environmental information across generationsare not well understood. In this study, we combined measures of antipredator responses (behavioural and morphological) withtranscriptomic investigations across two generations in the freshwater snail Physa acuta. We hypothesised that both within- andtransgenerational plasticity would induce phenotypic changes associated with differential gene expression. Our results con rmedwithin- and transgenerational plasticity: F1 snails respond to predator-cue exposure by increasing escape behaviour, reducing shelllength, and developing thicker and slenderer shells, whereas F2 snails from exposed parents have longer and thicker shells withnarrower apertures. Within- and transgenerational plasticity were accompanied by the differential expression of 112 genes (101 up- and11 downregulated) and 23 differentially expressed genes (17 up- and 6 downregulated), respectively. Within- and transgenerationalplasticity did not share common differentially expressed genes, but the associated molecular functions, involving metabolism andtranscription regulation, were similar. These results suggest that predator-induced within-generational plasticity and transgenerationalplasticity may result from different genomic pathways and may evolve independently.