For my dissertation, I examined the potential for and constraints on the evolution of tolerance in Asclepias syriaca. As a part of this investigation, I performed an experiment using A. syriaca in which foliar damage and soil nutrient concentration were manipulated. Under low nutrient conditions, significant genetic variation was detected for allocation patterns and for tolerance. Furthermore, resource allocation to storage was positively, genetically correlated with tolerance. Thus, in the low nutrient environment, tolerance was explained by resource allocation to storage. Under high nutrient conditions, allocation patterns did not predict tolerance, even though genetic variation in tolerance existed. The differences in outcomes between the two nutrient treatments highlight the importance of considering the possible range of environmental conditions which a genotype may experience.

I have also examined the consequences of herbivory on fruit abortion in Quercus alba. In this study, fruit abortion increased with increasing herbivory, suggesting that branch-level herbivore damage caused a decrease in fitness. In addition, higher canopy branches had a greater proportion fruit abortion compared to lower canopy branches even though no difference in level of damage existed between canopy heights. Thus, the cost of herbivore damage as measured on individual branches did not accurately describe the fitness costs of herbivory for the whole plant. The negative effect of herbivory on fruit set observed for upper canopy branches may have been reduced if the movement of carbohydrates was not restricted. Hence, functional constraints related to the modularity of woody plants appear to have exacerbated the negative effect of herbivore damage.

Presently, together with Bob Fritz, I am examining questions pertaining to tolerance to damage using a hybrid willow system. We hope to address questions regarding (1) which candidate traits confer tolerance to damage, (2) the selection gradient for candidate traits in F2 hybrids, (3) which sets of trait combinations are generally favored by selection, (4) the genetic architecture of tolerance and its traits, and (5) how plant age alters tolerance and its mechanisms.