Transcriptomic bases of within- and trans-generational predator-induced plasticity in the freshwater snail Physa acuta

Inducible defences in response to predation risk are a well-known example of adaptive phenotypic plasticity. While inducible defences have been mainly studied within a generation (within-generational plasticity), there is now clear evidence that the ancestral exposure to predation risk can influence the defences expressed by the offspring, even if they have not been exposed themselves (transgenerational plasticity). The molecular mechanisms allowing the transmission of environmental information across generations are still misunderstood. In this study, we combined measures of anti-predator responses (behavioural and morphological) with transcriptomic investigations across two generations in the freshwater snail Physa acuta . We hypothesised that both within- and transgenerational plasticity would induce phenotypic changes associated with differential gene expression. Our results confirmed within- and transgenerational plasticity: F1 snails have responded to predator-cue exposure by increasing escape behaviour, reducing shell length, and developing thicker and slender shells and F2 from exposed parents have shown similar responses. Within- and transgenerational plasticity were accompanied by the differential expression of 78 genes (77 up- and 1 down-regulated) and 14 differentially expressed genes (13 up- and 1 down-regulated), respectively. Within- and transgenerational plasticity did not share common differentially expressed genes but some differentially expressed genes in F1 are also highly expressed in F2 and overall, the molecular functions were similar, involving metabolism and transcription regulation. The quantitatively low molecular response associated with transgenerational plasticity suggests that gene expression changes induced by parental exposure may have occurred early in development and have decreased at adult stage.