Supporting data for the manuscript Inter-annual variation in the abundance of specialist herbivores determines plant resistance in Datura stramonium

The expression of plant resistance traits against arthropod herbivores often comes with costs to other essential plant functions such as growth and fitness. These trade-offs are shaped by the allocation of limited resources. However, plants might also possess the capability to allocate resources to both resistance and growth, thereby ensuring their survival when under herbivore attacks. Additionally, the extent of damage caused by herbivores could vary across different years or seasons, subsequently impacting plant performance. In this study, we aimed to investigate how the annual variations in herbivore abundance and damage levels affect plant performance. We generated F₂ progeny through a cross between two populations of the annual herb <i>Datura stramonium</i> (Solanaceae). These populations are known to have differing levels of chemical defense and herbivory. These F₂ plants were cultivated in a common natural environment for two consecutive years (2017 and 2018). Our findings reveal that plants with higher resistance, attained higher seed production but this trend was evident only during 2018. This relationship coincided with a five-fold increase in the abundance of <i>Lema daturaphila</i> (Chrysomelidae) larvae in 2018. Indeed, the plants experienced a 13-fold increase in damage during this second year of study. Furthermore, our results indicated that there was no trade-off between resistance, growth, and fitness in either of the two years. In contrast, during 2018, when plants faced stronger herbivore pressure, they allocated all available nutritional resources to enhance both resistance and growth. Our study highlights how the selection for plant resistance is dependent upon the inter-annual variation in herbivore abundance.

植物对抗植食性节肢动物（arthropod herbivores）的抗性性状表达，往往会对生长、适合度（fitness）等核心植物功能产生代价。此类资源权衡（trade-off）由有限资源的分配模式所决定。然而，植物或许同时具备为抗性与生长协同分配资源的能力，从而在遭受植食者攻击时保障自身存活。此外，植食者造成的损害程度可能随年份或季节而异，进而影响植株的生长与适合度表现。本研究旨在探究植食者种群丰度与损害程度的年际变化如何影响植株表现。本研究通过杂交两个一年生草本植物种群——洋金花（*Datura stramonium*，茄科Solanaceae）——的个体，获得了F₂子代。已知这两个种群的化学防御水平与植食者取食压力存在显著差异。将这些F₂植株种植于统一的自然环境中，连续开展两年（2017年与2018年）的栽培观测实验。研究结果显示，抗性更强的植株种子产量更高，但该趋势仅在2018年显现。该关联与2018年洋金花叶甲（*Lema daturaphila*，叶甲科Chrysomelidae）幼虫种群丰度提升五倍的情况相吻合。与此同时，实验第二年植株所受的植食损害程度提升了13倍。此外，研究结果表明，两年实验中均未发现抗性、生长与适合度之间存在资源权衡现象。与之相对，在2018年植株面临更强植食者压力时，它们会将所有可获取的营养资源同时用于提升抗性与生长。本研究揭示了植物抗性的选择压力如何依赖于植食者种群丰度的年际变化。