Plant scent and plant–insect interactions—Review and outlook from a macroevolutionary perspective

Abstract

The astonishing diversity of plants and insects and their entangled interactions are cornerstones in terrestrial ecosystems. Co-occurring with species diversity is the diversity of plant secondary metabolites (PSMs). So far, their estimated number is more than 200 000 compounds, which are not directly involved in plant growth and development but play important roles in helping plants handle their environment including the mediation of plant–insect interactions. Here, we use plant volatile organic compounds (VOCs), a key olfactory communication channel that mediates plant–insect interactions, as a showcase of PSMs. In spite of the cumulative knowledge of the functional, ecological, and microevolutionary roles of VOCs, we still lack a macroevolutionary understanding of how they evolved with plant–insect interactions and contributed to species diversity throughout the long coevolutionary history of plants and insects. We first review the literature to summarize the current state-of-the-art research on this topic. We then present various relevant types of phylogenetic methods suitable to answer macroevolutionary questions on plant VOCs and suggest future directions for employing phylogenetic approaches in studying plant VOCs and plant–insect interactions. Overall, we found that current studies in this field are still very limited in their macroevolutionary perspective. Nevertheless, with the fast-growing development of metabolome analysis techniques and phylogenetic methods, it is becoming increasingly feasible to integrate the advances of these two areas. We highlight promising approaches to generate new testable hypotheses and gain a mechanistic understanding of the macroevolutionary roles of chemical communication in plant–insect interactions.