Plant defence responses to volatile alert signals are population‐specific

Abstract

Herbivore‐induced volatiles are widespread in plants. They can serve as alert signals that enable neighbouring leaves and plants to pre‐emptively increase defences and avoid herbivory damage. However, our understanding of the factors mediating volatile organic compound (VOC) signal interpretation by receiver plants and the degree to which multiple herbivores affect VOC signals is still limited. Here we investigated whether plant responses to damage‐induced VOC signals were population specific. As a secondary goal, we tested for interference in signal production or reception when plants were subjected to multiple types of herbivore damage. We factorially crossed the population sources of paired Phaseolus lunatus plants (same versus different population sources) with a mechanical damage treatment to one member of the pair (i.e. the VOC emitter, damaged versus control), and we measured herbivore damage to the other plant (the VOC receiver) in the field. Prior to the experiment, both emitter and receiver plants were naturally colonized by aphids, enabling us to test the hypothesis that damage from sap‐feeding herbivores interferes with VOC communication by including emitter and receiver aphid abundances as covariates in our analyses. One week after mechanical leaf damage, we removed all the emitter plants from the field and conducted fortnightly surveys of leaf herbivory. We found evidence that receiver plants responded using population‐specific ‘dialects’ where only receivers from the same source population as the damaged emitters suffered less leaf damage upon exposure to the volatile signals. We also found that the abundance of aphids on both emitter and receiver plants did not alter this volatile signalling during both production and reception despite well‐documented defence crosstalk within individual plants that are simultaneously attacked by multiple herbivores. Overall, these results show that plant communication is highly sensitive to genetic relatedness between emitter and receiver plants and that communication is resilient to herbivore co‐infestation.