Heath Jeremy J, Kessler André, Woebbe Eric, Cipollini Don, Stireman John O
Department of Biological Sciences, Wright State University, 3640 Colonel Glenn Highway, Dayton, OH, 45435, USA.
Department of Ecology and Evolutionary Biology, Cornell University, 445 Corson Hall, Ithaca, NY, 14853, USA.
New Phytol. 2014 Jun;202(4):1357-1370. doi: 10.1111/nph.12755. Epub 2014 Mar 11.
Understanding the evolutionary reasons for patterns of chemical defense in plants is an ongoing theoretical and empirical challenge. The goal is to develop a model that can reliably predict how defenses are distributed within the plant over space and time. This is difficult given that evolutionary, ecological, and physiological processes and tradeoffs can operate over different spatial and temporal scales. We evaluated the major predictions of two leading defense theories, the growth-differentiation balance hypothesis (GDBH) and optimal defense theory (ODT). To achieve this, enemies, fitness components, terpenoids, and protease inhibitors were measured in Solidago altissima and used to construct conventional univariate and structural equation models (SEMs). Leaf-tissue value indices extracted from an SEM revealed a strong correlation between tissue value and terpenoid defense that supports ODT. A tradeoff between serine protease inhibition and growth as well as an indirect tradeoff between growth and terpenoids manifested through galling insects supported the GDBH. Interestingly, there was a strong direct effect of terpenoids on rhizome mass, suggesting service to both storage and defense. The results support established theories but unknown genotypic traits explained much of the variation in defense, confirming the need to integrate emerging theories such as pollination constraints, defense syndromes, tolerance, mutualisms, and facilitation.
理解植物化学防御模式的进化原因是一项持续存在的理论和实证挑战。目标是开发一个能够可靠预测防御如何在植物体内随空间和时间分布的模型。鉴于进化、生态和生理过程以及权衡可以在不同的空间和时间尺度上起作用，这一任务颇具难度。我们评估了两种主要防御理论——生长-分化平衡假说（GDBH）和最优防御理论（ODT）的主要预测。为实现这一目标，我们在加拿大一枝黄花中测量了天敌、适合度成分、萜类化合物和蛋白酶抑制剂，并用于构建传统的单变量和结构方程模型（SEM）。从结构方程模型中提取的叶组织价值指数显示，组织价值与萜类防御之间存在很强的相关性，这支持了最优防御理论。丝氨酸蛋白酶抑制与生长之间的权衡，以及通过瘿蚊表现出的生长与萜类化合物之间的间接权衡，支持了生长-分化平衡假说。有趣的是，萜类化合物对根茎质量有很强的直接影响，表明其对储存和防御都有作用。研究结果支持了既定理论，但未知的基因型特征解释了防御中大部分的变异，这证实了有必要整合诸如授粉限制、防御综合征、耐受性、共生关系和促进作用等新兴理论。
