Ecological and coevolutionary links between plant defence and plant reproduction

作为扎根于地面的无根生物，植物在受到食草动物和其他寄生虫的攻击时无法逃跑。相反，它们用一系列防御性化学物质来保护自己，这些化学物质使它们的叶子有毒或难吃。植物也不能主动寻找彼此繁殖；取而代之的是，他们招募蜜蜂、鸟类和蝴蝶来传递花粉，通常使用带有吸引人的化学物质气味的花朵。开花植物的非凡多样性可以说在植物生命的两个看似无关的方面最为明显：繁殖，以花的形式和功能的惊人多样性为例；还有防御，在大多数植物的叶子中发现的有毒化学物质的显著变化就是一个例子。因为植物既用它们的天然化学物质来阻止食草动物，又吸引传粉者，它们必须在这些功能之间取得平衡，通过在适当的时间在不同的组织中部署化合物。了解这种平衡对于理解和保护生物多样性，以及对作物物种的管理都很重要，因为大多数作物都受到敌人的攻击，需要传粉者。植物防御和繁殖一直被认为是两个独立的研究领域，食草动物对叶子防御的进化多样性有很大的贡献，而传粉者对花的颜色和气味有很大的贡献。令人惊讶的是，尽管对植物抗性性状进行了大量的研究，尽管越来越多的人担心管理和野生传粉媒介，特别是蜜蜂的丰度和多样性普遍下降，但很少有研究在基础或应用层面检查植物防御和繁殖之间的联系。然而，我最近的研究表明，植物防御和繁殖可能是内在联系的：特定的植物防御反应导致花的授粉效率降低，特定的繁殖模式决定了防御的类型。这些结果表明，与传统观点相反，食草动物可能实际上对花的性状施加了自然选择，而传粉者（和一般的植物繁殖）可能对叶子的防御施加了自然选择。本研究的目的是为了检验这些观点，目的是统一这两个研究领域。该项目将通过提出四个互补的问题来解决这个问题：首先，草食如何影响授粉，以及它如何因此影响花的进化和功能？第二，草食动物和传粉者在叶和花性状的自然选择中的相对重要性是什么？第三，什么生理机制将叶和花联系起来，以及这些机制如何或为什么在植物物种中有所不同？第四，不同的植物繁殖方式是否影响食草动物的进化？预计研究结果将揭示陆地生态系统中两种最普遍的物种相互作用（植食和授粉）之间的深层联系，从而改变我们对植物防御和生殖多样性的理解。

As sessile organisms rooted to the ground, plants can't run away when attacked by herbivores and other parasites. Instead, they defend themselves with an array of defensive chemicals that render their leaves toxic or unpalatable. Plants also can't actively seek each other out to reproduce; instead they recruit bees, birds and butterflies to transfer their pollen, often using flowers scented with attractive chemicals. The extraordinary diversity of flowering plants is arguably most evident in these two seemingly unrelated facets of a plant's life: reproduction, exemplified by the stunning diversity in flower form and function; and defence, exemplified by the remarkable variation in toxic chemistry found in the leaves of most plant species. Because plants use their natural chemicals both to deter herbivores and attract pollinators, they must strike a balance between these functions, by deploying chemical compounds in different tissues at the appropriate time. Understanding this balance is important for understanding and protecting biodiversity, and for the management of crop species, most of which are attacked by enemies and require pollinators.Plant defence and reproduction have been considered as separate research fields, with herbivores getting most of the credit for the evolutionary diversity of leaf defences and pollinators getting the credit for the colours and odours of flowers. Surprisingly little research has examined the links between defence and reproduction in plants, at either fundamental or applied levels, despite an enormous body of work on plant resistance traits, and despite growing concern over widespread declines in the abundance and diversity of both managed and wild pollinators, particularly bees. However, my recent research demonstrates that plant defence and reproduction may be intrinsically linked: Specific plant defence responses cause flowers to be less effectively pollinated, and specific modes of reproduction shape the types of defences that are deployed. These results suggest that, contrary to conventional wisdom, herbivores might actually impose natural selection on flower traits, while pollinators (and plant reproduction in general) might impose natural selection on leaf defences.The goal of this research is to test these ideas, with the goal of unifying these two research fields. The project will tackle this problem by asking four complementary questions: First, how does herbivory impact pollination, and how does it thereby influence the evolution and function of flowers? Second, what is the relative importance of herbivores and pollinators for natural selection on leaf and flower traits? Third, what physiological mechanisms link leaves and flowers, and how or why do those vary among plant species? Fourth, do different modes of plant reproduction influence the evolution of herbivores? The results are predicted to reveal deep connections between two of the most prevalent species interactions in terrestrial ecosystems (herbivory and pollination), and thereby transform our understanding of plant defensive and reproductive diversity.