Specificity of plant-plant communication: Kin recognition, plant sex, and herbivore identity

Background/Question/Methods

Plant-plant communication occurs when undamaged plants respond to airborne cues (i.e. volatile organic compounds) from damaged neighbors to increase or prime their defenses against future herbivore attack. There is increasing evidence that the complex blends of induced volatiles released by plants after herbivore attack may vary by plant genotype and/or sex, herbivore abundance and herbivore diet breadth and feeding guild (i.e. specificity of plant-plant communication). We investigated whether plant-plant communication is stronger within genetic clones (than among clones), between plants of the same sex (vs. between sexes), and between emitter-receiver plants attacked by the same herbivore species (vs. different herbivore species). We conducted independent greenhouse experiments using the long-lived, dioecious woody shrub Baccharis salicifolia (Asteraceae) in response to herbivory by two aphid species, the dietary specialist Uroleucon macolai and the dietary generalist Aphis gossypii. In both experiments, we assigned an emitter plant that was fed upon by one of the two aphid species in proximity to receiver plants. After an induction period, bioassays with both aphid species were conducted on the receiver plants, recording age at first reproduction, nymphs at first reproduction, and growth rate at 5th reproductive day.

Results/Conclusions

Our results showed that communication between B. salicifolia plants was highly specific of herbivore identity and emitter-receiver genetic relatedness, but was not specific to plant sex. Particularly, we found that emitter plants attacked by U. macolai decreased the performance of the U. macolai but not A. gosspyii on neighbor plants. The converse trend was observed for plants fed upon by A. gossypii. Communication was stronger when emitters and receivers were of the same clone. In contrast, communication was not influenced by whether plants were of the same or differing sex. Our results are consistent with several studies reporting that communication between plants is enhanced by genetic relatedness. Such dynamics might be attributed to the evolutionary benefits of communicating the risk of herbivory to kin or, alternatively, such signals may evolve as a form of within-plant communication. The herbivore specificity of plant communication is in turn likely to evolve as a cost-saving measure through the tailoring of defense to specific herbivores. In summary, this study demonstrates potentially adaptive specificity of induced resistance via neighboring plant volatiles with respect to both plant relatedness and herbivore identity.