Costs and Benefits of Anti-Herbivore Defenses in Aspen

University Of Wisconsin-Madison, Madison WI

Investigators

Abstract

0074427 Lindroth Plant defense against herbivory involves two principal traits: resistance and tolerance. A fundamental premise of plant defense theories is that such traits are costly, hence the existence of significant genetic variation in defense characteristics within plant populations. Demonstration of putative costs f defense however, has proved to be surprisingly difficult. Evidence supporting the notion of costs is equivocal and vanishingly small with respect to woody plant species. Over the last 15 years, research on quaking aspen has revealed (1) striking variation in susceptibility to outbreak insects, (2) equally striking genotypic variation in levels of phenolic glycosides, (3) phenolic glycosides reduce performance of aspen-feeding insects, (4) strong, environmentally-dependent trade-offs between growth and phenolic glycoside concentrations in aspen genotypes, and (5) preliminary evidence of genotypic variation in tolerance. The purpose of this research is to further investigate the costs and benefits of defense in the evolutionary ecology of aspen-insect interactions. One objective is to ascertain whether aspen resistance traits afford protection in experimental and natural settings. Levels of defoliation sustained by aspen genotypes are predicted to vary in inverse relation to phenolic glycoside concentrations. The experiment will be conducted in a common garden using clonally propagated aspen trees growing in nutrient-poor and nutrient-rich soil. Defoliation will be effected by addition of forest tent caterpillars. A second objective is to evaluate the independent and interactive roles of resistance and tolerance as defensive adaptations against herbivory. Aspen genotypes are predicted to exhibit costs of resistance and tolerance, and to exhibit negative genetic trade-offs between resistance and tolerance. This will be conducted in a common garden, with clonally propagated trees growing in nutrient-poor and nutrient-rich soils. This work is significant in that it will improve understanding of the evolution and ecology of plant defense against herbivores, and of factors constraining the evolution of defense systems. It constitutes the first in-depth, simultaneous evaluation of costs and benefits of chemical defense and tolerance in a woody plant. And, it involves species with expansive geographic ranges and pivotal ecological importance in early successional forests of North America.