Delayed greening – perhaps more descriptively called “early reddening” – is a striking phenomenon in which young leaves appear red, orange, or purple due to high levels of anthocyanins. This presents an interesting tradeoff: does it render young, vulnerable leaves more visible to potential herbivores, or does it signal better chemical defense against herbivory in expanding leaves. While these hypotheses have been tested in Paleotropical systems, no taxonomically broad study has examined the relationship between anthocyanin concentration and herbivory in Neotropical forests. To study this phenomenon in Costa Rican understory plants, I selected six woody species showing range of young leaf coloration. In each species, I measured anthocyanin concentration of young leaves and percent herbivory of young and mature leaves. Specifically, I asked 1) does anthocyanin concentration in young leaves predict observed herbivory? and 2) in species with delayed greening, do young leaves sustain less herbivory than mature leaves?
Results/Conclusions
I found that young leaves of delayed greening species sustained 1.3 – 8 times less herbivory than mature leaves, whereas there was no difference in herbivory between young and mature leaves in a control species without delayed greening, supporting the hypothesis that delayed greening may indicate chemical defenses in young leaves. Furthermore, anthocyanin concentration was negatively correlated with herbivory across sampled species. Herbivory of the six sampled species assorted into high and low herbivory groups; average anthocyanin concentration in the low herbivory group was almost twice as high as in the high herbivory group. By comparing herbivory and anthocyanin concentration across multiple species displaying delayed greening, this study presents a preliminary survey of delayed greening in Neotropical forests, and supports the hypothesis that higher concentration of anthocyanin in young leaves indicates better defenses against herbivory.
