Transgenerational plasticity of inducible defenses: combined effects of grand-parental, parental and current environments

While an increasing number of studies highlights that parental environment shapes offspring phenotype (transgenerational plasticity TGP), TGP beyond the parental generation has received less attention. Studies suggest that TGP impacts population dynamics and evolution of phenotype, but these impacts will depend on how long an environmental effect can persist across generations and whether multigenerational effects are cumulative. Here we tested the impact of both grand-parental and parental environments on offspring reaction norm in a prey-predator system. We exposed three generations of Physa acuta snails without and with predator-cues according to a full factorial design and measured offspring inducible defenses. We found that both grand-parental and parental exposure to predator cues impacted offspring anti-predator defenses, but their effects were not cumulative and depended on the defenses considered. We also highlighted that grand-parental environment could alter reaction norm of offspring shell thickness, demonstrating an interaction between the grand-parental TGP and the within-generational WGP plasticity. We called for more studies covering the combine effects of multigenerational environments.