The ecology and evolution of host plant range: butterflies as a model group

Historically, much of the impetus in the study of insect-plant interactions has come from the model group of butterflies and their hosts. Such studies raise some general questions: Why is there such a high degree of specializ ation on particular plants by egg-laying females? Do these plants represent the best, or even the only acceptable resources, in terms of offspring per formance? Have insects and plants coevolved? We outline results of research performed with a focus on the unusually polyphagous comma butterfly Polygo nia c-album. Results are reported and synthesized from the following. 1 A number of investigations on P. c-album itself. We stress the importance of varying outcomes of trade-offs between fitness parameters for the maint enance of polyphagy in this species, and the evolutionarily transient natur e of such a mechanism. 2 Comparisons between species in the tribe Nymphalini, illustrating that co nstraints on the gathering and processing of information are likely to be f actors of general importance in the evolution of specialization. 3 A phylogenetic study of Nymphalini. All taxa near the root of this tribe are specialists on the plant family Urticaceae and relatives. The host plan t range in the lineage leading to P. c-album was evidently later broadened to include other plant families such as Salicaceae, Betulaceae and Grossula riaceae, and this historical sequence of events seems to have consequences for the host plant preferences observed today. 4 A phylogenetic study covering the butterflies as a whole. We discuss the possibilities and limits for generalization to other insects.