Spatiotemporal interaction of risk‐spreading strategies for a seed‐dimorphic plant

Abstract For plants, the risk of stress‐induced reproductive failure can be spread temporally and spatially by increasing the variation in stress tolerance and dispersibility, respectively. Yet, we have limited understanding on how intraspecific stress tolerance can be interactively adjusted by these two risk‐spreading strategies. Seed‐dimorphic plants, which are frequently found in stressful and fluctuating environments, can produce dimorphic offspring with different stress tolerances and dispersibilities. Using a seed‐dimorphic Asteraceae, Synedrella nodiflora, we illustrated how maternal‐drought‐induced changes in drought tolerance and dispersibility may interactively increase intraspecific drought tolerance variation, and thus potentially improve adaptation to various water conditions. Maternal drought stress increased the mean or variation of drought tolerance of the less‐dispersible (R‐type) offspring, whereas it had variable effects on the drought tolerance of the more‐dispersible (D‐type) offspring depending on maternal seed morph (R‐type vs. D‐type) and habitat (dry vs. wet). Because the relative abundances of these two types of offspring remained largely unchanged by maternal drought, there was an overall increase in the intraspecific mean and variation of drought tolerance under maternal drought stress, driven by the changes in the less‐dispersible offspring. Synthesis. Our results indicate a strong interaction between stress tolerance variation and seed dispersibility in seed‐dimorphic plant species. Using drought tolerance as an indicator, we demonstrate a potential pathway for the adaptive evolution of seed‐dimorphic plants that may contribute to their wide distribution. More importantly, our findings highlight the ecological significance of seed dimorphism and the variation of stress tolerance to avoid reproductive failure under various environmental conditions.