Juenger Thomas, Bergelson Joy
Department of Ecology and Evolutionary Biology, University of Chicago, 1101 East 57th Street, Chicago, Illinois, 60637.
Mountain Research Station, University of Colorado, 818 County Road 116, Nederland, Colorado, 80466.
Evolution. 1998 Dec;52(6):1583-1592. doi: 10.1111/j.1558-5646.1998.tb02239.x.
Recent theoretical studies have argued that plant-herbivore coevolution proceeds in a diffuse rather than a pairwise manner in multispecies interactions when at least one of two conditions are met: (1) genetic correlations exist between plant resistances to different herbivore species; and (2) ecological interactions between herbivores sharing a host plant cause nonadditive impacts of herbivory on plant fitness. We present results from manipulative field experiments investigating the single and interactive fitness effects of three types of herbivory on scarlet gilia (Ipomopsis aggregata) over two years of study. We utilize these data to test whether selection imposed by herbivore attack on date of first flowering is pairwise (independent) or diffuse (dependent) in nature. Our results reveal complex patterns of the fitness effect of herbivores. Simulated early season browsing had a strong negative fitness effect on plants and also reduced subsequent insect attack. Surprisingly, this ecological interaction did not translate into significant interactions between clipping and insect manipulations on plant fitness. However, we detected a significant interaction between seed fly and caterpillar herbivory on plant fitness, with the negative effect of either insect being greatest when occurring alone. These results suggest that herbivore-imposed selection may have pairwise and diffuse components. In our selection analysis of flowering phenology, we discovered significant pairwise linear selection imposed by clipping, diffuse linear selection imposed by insects, and diffuse nonlinear selection imposed by clipping and insect attack acting simultaneously. Our results reveal that the evolution of flowering phenology in scarlet gilia may be in response to diffuse and pairwise natural selection imposed by multiple herbivores. We discuss the evolution of resistance characters in light of diffuse versus pairwise forms of linear and nonlinear selection and stress the complexity of selection imposed by suites of interacting species.
最近的理论研究认为，在多物种相互作用中，当满足以下两个条件中的至少一个时，植物与食草动物的协同进化是以扩散而非成对的方式进行的：（1）植物对不同食草动物物种的抗性之间存在遗传相关性；（2）共享宿主植物的食草动物之间的生态相互作用会导致食草作用对植物适合度产生非加性影响。我们展示了在为期两年的研究中，对三种食草作用对深红吉莉草（Ipomopsis aggregata）的单一和交互适合度影响进行操纵性田间实验的结果。我们利用这些数据来检验食草动物攻击对首次开花日期施加的选择在本质上是成对的（独立的）还是扩散的（依赖的）。我们的结果揭示了食草动物适合度效应的复杂模式。模拟的早季啃食对植物具有强烈的负面适合度效应，并且还减少了随后的昆虫攻击。令人惊讶的是，这种生态相互作用并未转化为修剪和昆虫操纵对植物适合度的显著交互作用。然而，我们检测到种子蝇和毛虫食草作用对植物适合度存在显著的交互作用，单独出现时，任何一种昆虫的负面影响都最大。这些结果表明，食草动物施加的选择可能具有成对和扩散的成分。在我们对开花物候的选择分析中，我们发现了由修剪施加的显著成对线性选择、由昆虫施加的扩散线性选择，以及由修剪和昆虫攻击同时作用施加的扩散非线性选择。我们的结果表明，深红吉莉草开花物候的进化可能是对多种食草动物施加的扩散和成对自然选择的响应。我们根据线性和非线性选择的扩散与成对形式来讨论抗性特征的进化，并强调由相互作用的物种组合施加的选择的复杂性。
