Micro- and macroevolutionary trade-offs in plant-feeding insects

A long-standing hypothesis asserts that plant-feeding insects specialize on particular host plants because of negative interactions (trade-offs) between adaptations to alternative hosts, yet empirical evidence for such trade-offs is scarce. Most studies have looked for microevolutionary performance trade-offs within insect species, but host-use could also be constrained by macroevolutionary trade-offs caused by epistasis and historical contingency. On the other hand, evolutionary interactions between adaptations to diverse hosts could be neutral or positive rather than negative. Here we used a phylogenetic approach to estimate the micro-and macroevolutionary correlations between use of alternative host plants within two major orders of plant-feeding insects: Lepidoptera (caterpillars) and Hemiptera (true bugs). Across 1604 caterpillar species, we found both positive and negative pairwise correlations between use of diverse host taxa, with overall network patterns suggesting that different host-use constraints act over micro-and macroevolutionary timescales. In contrast, host-use patterns of 955 true bug species revealed uniformly positive correlations between presence on the same host taxa over both timescales. The lack of consistent patterns across timescales and insect orders indicates that host-use trade-offs are historically contingent rather than universal constraints. Moreover, we observed few negative correlations overall despite the wide taxonomic and ecological diversity of the focal host taxa, suggesting that positive interactions between host-use adaptations, not trade-offs, dominate the long-term evolution of host use in plant-feeding insects.