Predictable ecological and evolutionary drivers of herbivore induced plant volatiles: A meta-analysis

Herbivore-induced plant volatiles (HIPVs) mediate critical ecological functions, but no studies have quantitatively synthesized data published on HIPVs to evaluate broad patterns. We analyzed how domestication affects volatile release. We predicted that a history of cultivation should decrease volatile emission as it is thought defense capability is lost in favor of yield. To test this hypothesis, we extracted data from 236 experiments that report volatiles produced by herbivore-damaged and undamaged plants. These data were subjected to meta-analysis, including effects on total volatiles and major biochemical classes, and changes in the number of volatile compounds released. We found that contrary to our expectation domesticated species induced green-leaf volatiles and sesquiterpenes more strongly than wild species. However, domesticated plants produced fewer volatile compounds.  We also conducted these same analyses in a subset of our data (Brassicaceae and Solanaceae), and found that green-leaf volatiles continued to be more highly induced by domesticated plants. The hypothesis that plants lose their defensive ability in response to domestication is driven by the assumed costs of such defenses. However, volatiles may represent a relatively cheap defense with fewer fitness consequences than previously thought and other traits associated with domestication contribute to the effects of cultivation on indirect defense. Despite the large number of experiments, we identified several gaps in the existing literature that should guide future investigations into the effects of domestication on volatile emission, including more studies that control the amount of damage between domesticated and wild comparisons, and more phylogenetically diverse HIPV experiments.