​Supra-specific Janzen-Connell effects:
​Constraints to insect herbivore specificity and performance

Plants possess complex suites of evolved defensive traits which serve to determine their palatability for insect herbivores (Fig. 1), and in turn the specificity of insects feeding on them. From the evolutionary perspective, the need to avoid sharing specialized herbivores should promote divergence in defensive strategies among closely related hosts, such as the investment into constitutive vs. induced defenses. This may increase the potential for an insect specificity and performance gradient across congeneric hosts, potentially affecting negative density dependence effects among closely related plants. Within this collaborative project, we take two complementary approaches to manipulate the chemical landscape faced by insect herbivores. Our first objective is to examine whether highly specific induced defenses promote evolutionary divergence in defensive strategies in large tree genera (Ficus, Syzygium, and Macaranga), and hence lower negative density dependence effects in the spatial distribution of species with divergent defenses. Our second objective is to relocate the insects themselves across increasing phylogenetic and chemical distances from their primary hosts.
Fig. 1. A. Variation in caterpillar communities explained by Ficus, Macaranga, and Syzygium polyphenol profiles, B: Food-web between focal plants and caterpillars.
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