Coevolution: Plant-herbivore interactions and secondary metabolites of plants

Abstract

Plant-herbivore interaction has long been a central model to explain the evolutionary success of vascular plants and insects, and the extraordinary diversity of secondary compounds produced by plants. Coevolutionary theory proposes that herbivorism has spur diversification and speciation of host-plants and phytophagous animals through an arms race, which results in a general concordance on their phylogenies, and the evolution of diverse (mostly defensive) chemical compounds by plants and counter-defenses by herbivores. Main assumptions of the micro- and macroevolutionary postulates of the coevolutionary model have been extensively tested within populations and along phylogenies. Common patterns found indicate that plants and herbivores constitute a selective context for each other, and that plant secondary metabolites are adaptations that constraint phytophagous insects to use a plant as a host or as a food source. Herbivorism is strongly implicated in the evolution of specialized associations that are usually mediated by a conserved biochemical machinery of host-plants. The evolution of specialism appears to be correlated to speciation events and even with adaptive radiations. However, there is little evidence that these correlations reflect a causal relationship. Perhaps the most compelling evidence linking macroevolutionary patterns and mechanisms that produce new species is the matching of the genetic machinery responsible for the evolution of chemical novelty on plants and major emergency events of plants and herbivore lineages. This body of work developed from the study of the antagonistic association of plants and herbivores in more than 60 years has evince the great potential of adaptive evolution to generate much of the Earths’ biodiversity.