Ecological and coevolutionary links between plant defence and plant reproduction

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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.