Two sides of the same coin: Conditional outcomes and conflicting selection pressures in plant-pollinator-herbivore interactions

Plant-animal interactions are thought to have played a key role in the diversification of angiosperms, but plant-herbivore and plant-pollinator interactions have historically been studied independently. Many insects function as pollinating adults but have herbivorous larvae, providing the potential for mutualist interactions to have negative consequences if pollinators oviposit their offspring on preferred plants. The role of floral traits in determining the outcome of this interaction, ranging from pollination to herbivory, is largely unexplored outside of a few highly specialized systems. Furthermore, if traits such as defensive chemicals are correlated in leaves and floral tissue, it may be difficult for plants to evolve optimal solutions to conflicting selection pressures for attractive flowers and defended leaves. Here I review literature and present data examining the extent to which plants encounter conflicting tradeoffs between attracting pollinators while deterring herbivores, the role of plant traits in determining the outcome of interactions that range from pollination to herbivory, the potential for conflicting selection pressure due to correlated traits across tissues, and the role of abiotic environment in altering expression of defensive and attractive phenotypes. This body of information will be used to explore and understand how conditional outcomes of interactions historically thought to be mutualisms may shape the ecology and evolution of plant resistance and attractive traits.