Resource availability and predator cues shape within- and transgenerational reaction norms.

The main dilemma facing prey is how to reduce predation risk while acquiring resources. Phenotypic plasticity, by modulating traits for acquiring resources and for defences, is a key process driving this trade-off. While there is ample evidence that predator-induced within-generational plasticity depends on resources, the relationship between resources and predator-induced transgenerational plasticity (TGP) remains understudied. This study investigated how predator exposure and resource availability influence within-generational plasticity and TGP. We based our predictions on theories related to information- and state-based plasticity, two kinds of plasticity occurring in response to environmental information or alteration affecting somatic state, respectively. We conducted a two-generation laboratory experiment in the freshwater snail Physa acuta, manipulating predator cues and resource availability. Our results revealed that both types of plasticity participate in shaping the within- and transgenerational responses. Within a generation, the limited resource decreased the somatic state but did not constrain the defences. Across generations, the poor parental state decreased the offspring state even in high-resource conditions, which in turn decreased the absolute levels of their defences but increased their investment in reproduction. These results highlight the importance of integrating informational and state-based effects across generations to provide a more complete understanding of prey responses to predators.