SG: Growth-defense tradeoffs, context dependency and genetic variation in aspen: implications for plant-insect interactions

University Of Wisconsin-Madison, Madison WI

Investigators

Abstract

Genetic diversity is important to the health of forest ecosystems, but the factors that influence such diversity remain poorly understood. This research will address how genetic diversity is affected by trees' ability to grow and defend themselves against insect attack, and by competition from neighboring trees for resources. Also, forest productivity will be explored in light of genetic diversity. The research will take place in experimental stands of aspen, where trees have been grown for several years at different densities and then subjected to an outbreak of leaf-eating caterpillars. This work will advance scientific knowledge of how best to manage forests to maximize production, while also minimizing insect damage. Results from this research will be particularly relevant to regions where aspen populations are in widespread decline. The project will train undergraduate and graduate students in biological science and promote mentoring of high school and college students from groups that are currently under-represented in science. This research will explore how environmentally mediated growth-defense tradeoffs in a foundation plant species influence intraspecific (genotypic) variation and, in turn, how genotypic variation shapes stand-level productivity and resistance to insect attack. Aspen exhibits striking genotypic variation in physiology, growth and chemical defense, and strong negative genotypic correlations between growth and defense. How such tradeoffs influence selection to shape the genetic architecture of plant populations is largely unknown. An array of experimental aspen stands, each containing 16 genotypes and subjected to low or high intraspecific competition intensity (CI), will be used to test hypotheses concerning: 1) phenotypic expression of leaf physiological and chemical traits under low vs. high CI, 2) shifts in the genotypic composition of aspen stands as a consequence of competition-mediated selection for growth vs. defense traits, and 3) effects of genotypic divergence on stand resistance to defoliation by forest tent caterpillars. Hypothesis testing will incorporate measures of aboveground growth, photosynthesis and foliar chemical defenses, as well as assessments of stand-level defoliation by tent caterpillars. This research will advance understanding of the ecological and evolutionary factors that influence the distribution, genetic composition, and function of forest ecosystems.