Behaviour is a labile and reversible trait allowing a rapid response to environmental changes. Evidence is accumulating that individuals differ in the degree and extent of behavioural plasticity, even within a same population. What is the role of past environmental conditions on between-individual differences in this form of phenotypic plasticity is still not well understood. Although previous environments experienced by animals themselves can be a source of between-individual difference in behavioural responses, less is known about the effect of ancestral environment. Ancestral environment can indeed have long-lasting effects on offspring phenotype (e.g. morphology) and some studies showed such effects on average behavioural responses. These transgenerational carry-over effects (called transgenerational plasticity) could also influence the between-individual variation in behavioural plasticity. In this context, we used the concept of behavioural reaction norms to study how intra- and transgenerational carry-over effects influence between-individual variation in both personality and level of behavioural plasticity (respectively intercept and slope of the behavioural reaction norm).

We investigated the behavioural reaction norms of the freshwater snail Physa acuta in response to predator cues according to past (intra- and transgenerational) experience of predation risk. This species is known to increase its survival by expressing anti-predator behaviours (especially crawling-out the water) when the predator is detected. Moreover, as this species has a short generation time, parental environment should be a good proxy of offspring environment in the wild, and transgenerational carry-over effects should have been selected. Two generations (parental and offspring generations) were raised in control or predator-cue environments. We then measured in all mature offspring two behavioural traits in control and in predator-cue environments: exploration (total distance crawled in the water) and escape behaviour (time to crawl out the water).