The evolution of defenses

My research has focused on the evolution of chemical defenses in multiple tissues. Herbivore interactions vary across the plant; I'm interested in how this heterogeneous selection shapes tissue specificity of defenses. To study this, I use Boechera stricta, a wild mustard. Like many mustards, B. stricta makes several types of glucosinolates, chemical defenses against herbivores. These defenses vary within the plant. Using a combination of lab, greenhouse, and field work, I've studied how glucosinolates vary within the plant and how tissue specificity responds to selection.

Study system
Boechera stricta is a short-lived perennial native to western North America. A close relative of Arabidopsis thaliana, it offers extensive genetic and genomic resources, including a GWAS population of 500 genotyped families. B. stricta has grown in relatively undisturbed habitats for 4,000 years, developing long-term local adaptation and interactions. 
B. stricta is attacked by a number of insect herbivores, which feed on leaves, stems, buds, flowers and fruits. Herbivory, particularly on reproductive tissues, can have a large effect on plant fitness. One of the main defenses against herbivores are glucosinolates, also known as mustard oils. B. stricta makes up to four different types of glucosinolates; which types are made has been shown to affect herbivore damage. I've found significant variation in both concentration and types of glucosinolates between different plant tissues; leaves and fruits vary in their defenses.

Constraint in the evolution of defenses
Interactions with herbivores vary within the plant. Is it possible for plants to evolve effective defenses against all enemies?

Using a quantitative genetics framework, I asked whether covariances between glucosinolate profile in each tissue constrained the response to selection throughout the plant. In order to test the effects of covariances, I performed a large-scale field experiment, using 100 genotypes collected from one population, grown in a common garden located within that population. I measured herbivory, fitness, and glucosinolate traits in the field.