Data from: Optimal foraging by herbivores maintains polymorphism in defence in a natural plant population

1. Many species of plants and animals exhibit polymorphism for defensive traits. Adaptive foraging by natural enemies has long been hypothesized to maintain such polymorphism, but this has not been clearly demonstrated in a natural prey or host population. 2. The purpose of this study was to address whether the brassica leaf beetle Phaedon brassicae promotes the maintenance of defence polymorphism in the trichome-producing (hairy) and trichomeless (glabrous) morphs of Arabidopsis halleri subsp. gemmifera. Here, we modelled foraging behaviours of herbivores and demography of the host plant. Then, we estimated the model parameters based on the likelihood of observed data from a natural A. halleri population. 3. The patterns of leaf damage to hairy and glabrous plants were well explained when we presumed the optimal diet choice by P. brassicae. The observed dynamics in the plant number and morph frequency were well supported by the model with the estimated parameter values. Our numerical analysis showed that the optimal diet choice by P. brassicae caused a negative frequency-dependent selection on trichrome dimorphism. The coexistence of two morphs was allowed over a wide range of herbivory pressure and the cost of defence. 4. These results indicate that the optimal diet choice by P. brassicae contributes to the coexistence of hairy and glabrous A. halleri. While species interaction and stochastic dispersal are both involved in polymorphism dynamics in the field, our findings suggest that the role of consumer behaviours in the maintenance of defence polymorphism may be more important than currently appreciated.1. 诸多动、植物类群均展现出防御性状多态性。长期以来，学界假说认为天敌的适应性觅食行为可维持此类多态性，但此前尚未在自然猎物种群或宿主种群中得到明确验证。 2. 本研究旨在探究十字花科叶甲菜心萤叶甲（*Phaedon brassicae*）是否能够维持球芽拟南芥（*Arabidopsis halleri* subsp. *gemmifera*）产毛状体（trichome）型（多毛型）与无毛状体型（glabrous，光滑型）的防御性状多态性。本研究首先构建了植食性昆虫的觅食行为模型与宿主植物的种群统计学模型，随后基于自然种群的观测数据似然值估算模型参数。 3. 当假定菜心萤叶甲存在最优食谱选择行为时，多毛型与光滑型植株的叶片损伤模式可得到良好拟合。基于估算参数构建的模型，能够较好地复现观测到的植株数量与形态型频率的动态变化。本研究的数值分析结果显示，菜心萤叶甲的最优食谱选择会对毛状体二态性产生负频率依赖选择作用。在广泛的植食压力与防御成本范围内，两种形态型均可实现共存。 4. 上述结果表明，菜心萤叶甲的最优食谱选择行为有助于多毛型与光滑型球芽拟南芥的共存。尽管野外环境中的多态性动态同时受物种间相互作用与随机扩散过程的影响，但本研究结果提示，消费者行为在维持防御性状多态性中的作用，或许比当前学界所认知的更为重要。