Simms Ellen L, Rausher Mark D
Department of Zoology, Duke University, Durham, NC, 27706.
Evolution. 1989 May;43(3):573-585. doi: 10.1111/j.1558-5646.1989.tb04253.x.
An important component of the process of coevolution between plants and their insect herbivores is the imposition of selection on plants by insects. Although such selection has been inferred from indirect evidence, little direct evidence for it exists. One goal of this study was to seek direct evidence by determining, for a single plant-herbivore system, whether insect herbivores impose selection on their host plants. A second goal was to determine whether costs are associated with genotypes that confer resistance to herbivores, as has been commonly postulated. The annual morning glory, Ipomoea purpurea, exhibits genetic variation in resistance to four different types of insects. For three of these types, most of the genetic variation is additive. Removal of insect herbivores increased the number of seeds produced by I. purpurea by 20% and eliminated additive genetic variation for seed number (fitness). This result implies that herbivores impose selection on some trait(s) of their host plants. Coupled with selection for decreased damage by corn earworms, as revealed by a negative additive genetic covariance between damage and fitness, this result suggests that insect herbivores impose selection on resistance to corn earworms in I. purpurea. Two types of cost of resistance to herbivores were sought in I. purpurea: 1) internal trade-offs in allocation of resources and 2) ecological trade-offs between resistances to different insects. No costs of either type were detected. This result suggests that cost-benefit arguments that attempt to predict the evolution of levels of resistance to herbivores are not applicable to I. purpurea.
植物与其食草昆虫之间协同进化过程的一个重要组成部分是昆虫对植物施加选择。尽管这种选择已从间接证据中推断出来，但几乎没有直接证据。本研究的一个目标是通过确定对于单一植物 - 食草动物系统，食草昆虫是否对其寄主植物施加选择来寻找直接证据。第二个目标是确定是否如通常所假设的那样，与赋予抗食草动物能力的基因型相关的代价存在。一年生牵牛花，即紫牵牛，在对四种不同类型昆虫的抗性方面表现出遗传变异。对于其中三种类型，大部分遗传变异是加性的。去除食草昆虫使紫牵牛产生的种子数量增加了20%，并消除了种子数量（适合度）的加性遗传变异。这一结果意味着食草动物对其寄主植物的某些性状施加了选择。再加上玉米螟造成的损害与适合度之间存在负加性遗传协方差，表明对玉米螟损害的选择减少，这一结果表明食草昆虫对紫牵牛中对玉米螟的抗性施加了选择。在紫牵牛中寻找了两种抗食草动物的代价类型：1）资源分配的内部权衡，以及2）对不同昆虫抗性之间的生态权衡。未检测到任何一种类型的代价。这一结果表明，试图预测抗食草动物抗性水平进化的成本效益论点不适用于紫牵牛。
