Plant response to touch vs. insect feeding vibrations

Plants experience a wide variety of mechanical stimuli in their environment, some of which indicate the presence of herbivory. Insect feeding vibrations elicit direct and primed increases in levels of defensive compounds. Touch is also a mechanical stimulus arising from rain, wind, and the movement of herbivores and pollinators. In this study, we compared the effect of insect feeding vibrations on flavonoid defenses with two other mechanical stimuli, a silent sham treatment and an active touch treatment. Feeding vibrations caused a direct increase in the concentration of anthocyanins compared to silent sham and active touch, and elicited no priming effects on response to methyl jasmonate. Silent sham caused a priming increase in the concentration of flavonols compared to feeding vibrations and active touch, and there were no direct effects. Although these results provide additional evidence for plant discrimination among mechanical stimuli, we discuss the common intertwining of touch and vibration in what plants experience in natural environments. We propose that touch and vibration are likely perceived by plants as related mechanical stimuli, and encourage broader exploration of this core feature of plant sensory ecology.