Data from: Costs of resistance and correlational selection in the multiple-herbivore community of Solanum carolinense

Although a central assumption of most plant-defense theories is that resistance is costly, fitness costs have proven difficult to detect in the field. One useful, though labor-intensive, method to detect costs is to quantify stabilizing selection acting on resistance in field populations. Here, we report on an experimental field study of Solanum carolinense in which we employed a quadratic phenotypic-selection analysis on 12 types of resistance (defined operationally as one minus the proportion of tissue damaged) involving nine species of herbivores. For seven types of resistance, we found significant stabilizing selection and intermediate optimum levels, indicating the existence of fitness costs. These costs were greatest for resistance against frugivores, moderate for florivores, and lowest for folivores. In addition, significant correlational selection gradients were found for ten pairs of resistance measures, which we interpret as evidence that the fitness impacts of these pairs of herbivores combined non-additively. When the herbivores fed on the same type of tissue, their impact was synergistic (greater than additive), and when they fed on different tissues, their impact was antagonistic (less than additive). We suggest this may be a general pattern for correlational selection on resistance to different herbivores.

尽管多数植物防御理论的核心假设为抗性存在适应性代价（fitness costs），但在自然野外环境中却难以检测到此类代价。一种虽耗费大量人力的有效检测方法，即量化田间种群中作用于抗性的稳定选择（stabilizing selection）。本研究针对卡罗林茄（Solanum carolinense）开展了田间实验：我们针对9种植食性生物（herbivores）对应的12类抗性开展了二次表型选择分析（quadratic phenotypic-selection analysis），这类抗性的操作定义为1减去组织受损比例（proportion of tissue damaged）。针对其中7类抗性，我们检测到了显著的稳定选择与中间最优水平，证明了适应性代价的存在。此类代价的强度差异显著：针对食果动物（frugivores）的抗性代价最高，针对食花动物（florivores）的代价次之，针对食叶动物（folivores）的代价最低。此外，我们在10组抗性指标中检测到了显著的相关选择梯度（correlational selection gradients），我们认为这表明该组植食性生物对适合度的影响存在非加性组合效应：当植食性生物取食同一类型组织时，二者的影响呈协同效应（大于加性效应）；当它们取食不同组织时，影响则呈拮抗效应（小于加性效应）。我们推测，这一模式或许是针对不同植食性生物的抗性相关选择的通用规律。