Parental herbivory shapes offspring performance across genotypes in an invasive clonal plant

Parental environmental effects play a crucial role in clonal plants, potentially enabling clonal offspring to pre-adapt to environmental changes. However, few studies have examined whether such parental effects differ between genotypes and whether they enhance both growth and defence. We conducted a two-generation herbivory experiment using six genotypes of the invasive clonal plant Hydrocotyle verticillata and the native generalist herbivore Spodoptera litura in China. We tested how parental herbivory (PH) effects influence offspring survival, growth, and herbivory defence, and whether these parental effects vary among genotypes. Herbivory significantly reduced leaf mass and leaf number of parental plants, while increasing its specific leaf area. PH enhanced offspring survival by 21% and tended to increase offspring leaf mass. However, clonal offspring from herbivory-treated parental plants suffered equally severe defoliation (>95%) as control offspring. While most parental effects were consistent across genotypes, root mass and specific leaf area showed genotype-dependent responses. Notably, genotype G4 exhibited markedly elevated SLA following PH despite having the lowest offspring survival. Our results reveal an asymmetric transgenerational strategy in invasive H. verticillata, that is, PH enhances offspring growth and survival without conferring herbivory defence. This decoupling of growth enhancement from defence induction represents an evolutionary trade-off that may facilitate rapid colonization but leaves invasive populations vulnerable to herbivore pressure. Consequently, while this transgenerational plasticity facilitates range expansion and population establishment in herbivore-free habitats, it may render invasive populations susceptible to regulation by specialist or generalist herbivores during secondary contact.