Evolutionary dynamics of host-plant specialization: A case study of the tribe Nymphalini

Two general patterns that have emerged from the intense studies on insect-h ost plant associations are a predominance of specialists over generalists a nd a taxonomic conservatism in host plant use. In most insect-host plant sy stems, explanations for these patterns must be based on biases in the proce sses of host colonizations, host shifts, and specialization, rather than co speciation. In the present paper, we investigate changes in host range in t he nymphalid butterfly tribe Nymphalini, using parsimony optimizations of h ost-plant data on the butterfly phylogeny. In addition, we performed larval establishment tests to search for larval capacity to feed and survive on p lants that have been lost from the female egg-laying repertoire. Optimizati ons suggested an ancestral association with Urticaceae, and most of the tes ted species showed a capacity to feed on Urtica dioica regardless of actual host-plant use. In addition, there was a bias among the successful establi shments on nonhosts toward plants that are used as hosts by other species i n the Nymphalini. An increased likelihood of colonizing ancestral or relate d plants could also provide an alternative explanation for the observed pat tern that some plant families appear to have been colonized independently s everal times in the tribe. We also show that there is no directionality in host range evolution toward increased specialization, that is, specializati on is not a dead end. Instead, changes in host range show a very dynamic pa ttern.