Community structure of insect herbivores is driven by conservatism, escalation and divergence of defensive traits in Ficus

Escalation (macroevolutionary increase) or divergence (disparity between relatives) in trait values are two frequent outcomes of the plant/herbivore arms race. We studied the defenses and caterpillars associated with 21 sympatric New Guinean figs. Overall caterpillar community structure correlated with alkaloid diversity, latex proteases, oxidative activity and trichomes. Generalists were concentrated on hosts with low levels of protease and oxidative activity, while the distribution of specialists correlated to phylogeny, protease and trichomes. A model of Brownian motion (phylogenetic conservatism) best approximated the evolution of proteases, while alkaloid diversity has clearly escalated globally, and oxidative activity has escalated locally. Trichomes were a divergent trait. Herbivore specificity determines their response to host defenses: escalating traits affect generalists and divergent traits specialists. Correspondingly, the evolution of defenses in Ficus is dependent on herbivore specificity. Over time escalating defenses are circumvented or utilized, we found one genus of aposematic specialists restricted to highly alkaloidal hosts.