| dc.description.abstract |
<p>In order to deter herbivores, plants evolve defenses suited to different tissues
and varying patterns of herbivory. If the defense profiles of different tissues share
common genetic controls but differ in selective pressures, evolution of effective
defenses within the whole plant may be constrained. In my dissertation, I investigate
how glucosinolates, biologically active secondary metabolites, evolve in multiple
tissues of the crucifer Boechera stricta. I quantify variation in glucosinolate concentration
and the relative ratio of each glucosinolate compound (hereafter called the glucosinolate
profile) between leaves and fruits and find support for the optimal defense hypothesis,
which predicts a higher concentration of glucosinolates in higher-value tissues. Using
a large-scale common garden experiment within a population, I demonstrate that antagonistic
selection between tissues and genetic covariances in glucosinolate profile between
leaves and fruits exercise strong constraint on the evolution of defenses. Additionally,
I compare the structure of genetic variances and covariances (the G-matrix) among
four genetically differentiated groups of B. stricta and find that the structure of
the G-matrix can be altered within approximately 5,000 generations. An Fst-Qst analysis
reveals that some differences in glucosinolate profile between were driven by selection.</p>
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