PHENOTYPE MATCHING IN WILD PARSNIP AND PARSNIP WEBWORMS: CAUSES AND CONSEQUENCES

Behavioral assays for studies of host plant choice and adaptation in herbivorous insects

The association of insect herbivores with their host plants is influenced by behaviors governing acceptance of those plants for feeding and oviposition. Behavioral changes accompany and may even precede host range expansion. Characterization and quantification of specific behaviors often form the basis of studies on host plant adaptation and chemical ecology. Behavioral assays of insects are usually designed to measure attraction for feeding or oviposition in relation to their host plants or specific chemistry. We review behavioral assays of insect herbivores with host plants or the volatiles they emit, with special consideration given to design, analysis, and interpretation to maximize ecological relevance. A toolkit of robust assays can help address fundamental issues at the intersection of ecology and evolution, such as the underpinnings of plant-insect interactions and the identification of genes involved in host race formation.

Evolution of plant defenses in nonindigenous environments

Exotic plants provide a unique opportunity to explore the evolution of defense allocation in plants. Many studies have focused on whether enemy release leads to a change in defense allocation. Little research has focused on induced defenses and on how resource availability in the nonindigenous range might cause evolutionary shifts in defense trait allocation. We examine (a) the major evolutionary hypotheses predicting defense expression in plants, (b) the hypotheses explaining defense evolution of exotic species, and (c) the importance of geographic variation in ecological interactions to defense evolution (geographic mosaics). In addition, we review the strengths and weaknesses of experimental approaches, present case studies, and suggest areas that deserve further attention.

Role of coevolution in generating biological diversity: spatially divergent selection trajectories

The Geographic Mosaic Theory of Coevolution predicts that divergent coevolutionary selection produces genetic differentiation across populations. The 29 studies reviewed here support this hypothesis as they all report spatially diverged selection trajectories which have generated variable outcomes in the interaction traits among populations. This holds for both mutualistic interactions such as those between host plants and their root symbionts, or plants and their pollinators, as well as for antagonistic interactions such as plants and their pathogens or herbivores. Most often, it is the strength of selection that varies across landscapes. Variation may be generated by both the physical environment (namely temperature), and the local community--competitors, parasites, and alternative hosts--that intensify or dilute selection locally for a wide range of species interactions. At its extreme, selection trajectories may be reversed with an antagonistic interaction being commensalistic in some populations and mutualistic in yet others, depending on the local community context. Selection trajectories were found to diverge among continents, but also more locally among neighbouring populations and even within a single population. This result highlights the importance of coevolutionary selection generating biological diversity with far-reaching implications for both biodiversity conservation as well as applied biology.