Mauricio Rodney, Rausher Mark D
Department of Zoology, Duke University, Durham, North Carolina, 27708-0325.
Evolution. 1997 Oct;51(5):1435-1444. doi: 10.1111/j.1558-5646.1997.tb01467.x.
Although biologists have long assumed that plant resistance characters evolved under selection exerted by such natural enemies as herbivores and pathogens, experimental evidence for this assumption is sparse. We present evidence that natural enemies exert selection on particular plant resistance characters. Specifically, we demonstrate that elimination of natural enemies from an experimental field population of Arabidopsis thaliana alters the pattern of selection on genetic variation in two characters that have been shown to reduce herbivore damage in the field: total glucosinolate concentration and trichome density. The change in pattern of selection reveals that natural enemies imposed selection favoring increased glucosinolate concentration and increased trichome density, and thus, supports one of the major assumptions of the coevolution hypothesis. We also demonstrate that a pattern of stabilizing selection on glucosinolate concentration results from a balance between the costs and benefits associated with increasing levels of this resistance character. This result provides direct confirmation of the appropriateness of cost-benefit models for characterizing the evolution of plant defenses.
尽管长期以来生物学家一直认为，植物的抗性特征是在诸如食草动物和病原体等天敌施加的选择作用下进化而来的，但这一假设的实验证据却很稀少。我们提供了证据表明，天敌会对特定的植物抗性特征施加选择。具体而言，我们证明，从拟南芥的一个实验田间种群中去除天敌，会改变对两个已被证明能在田间减少食草动物危害的性状的遗传变异的选择模式：总芥子油苷浓度和毛状体密度。选择模式的变化表明，天敌施加的选择有利于增加芥子油苷浓度和增加毛状体密度，因此，支持了协同进化假说的一个主要假设。我们还证明，芥子油苷浓度的稳定选择模式是由与这种抗性特征水平增加相关的成本和收益之间的平衡导致的。这一结果直接证实了成本效益模型在描述植物防御进化方面的适用性。
