Plants balance the benefits of chemical-based defenses against the cost of producing such defenses. Plant defense theory predicts that constitutive defenses should be favored in environments with reliably high herbivore pressure, while inducible defenses should be favored in unpredictable environments. In lowland neotropical rainforests, baseline rates of herbivory are consistently high, which should favor constitutive, non-plastic defense phenotypes. I used ten canopy tree species from seven different families in the tropical lowland forests of Peru to test the prediction that their leaves would be unresponsive to a standardized chemical elicitor, methyl jasmonate (MeJA; 25mM). I accessed leaves of each species using an existing canopy walkway, and sampled headspace volatiles non-destructively and after leave crushing to damage-released volatiles.
Results/Conclusions
In the absence of MeJA, leaves of all species generally emitted few volatiles from undamaged leaves. However, more basal plant species emitted a diverse set of constitutive damage-mediated volatile profiles. Interestingly, all ten species induced volatile emissions from undamaged leaves after MeJA application, and the dominant compound identities were nearly identical. Moreover, the total amount of MeJA-induced volatiles—but not the amount of natural herbivory on the leaves—scaled with the number of constitutive damage-mediated volatiles, suggesting a tradeoff in constitutive and inducible defense strategies among sympatric, unrelated canopy trees in a lowland tropical rainforest.