Abstracts (first author)
Selection on the genes that control complex traits
How does environmental heterogeneity influence growth, reproduction, and fitness in genetically variable plant populations? In Boechera, a wild relative of Arabidopsis, we used genome-wide markers to quantify selection coefficients at polymorphic loci throughout the life cycle, across multiple sites and years. We found strong natural selection that varied among environments, with stronger selection on reproduction than on survival components of fitness.
Next, we cloned a QTL that controls defensive chemistry, damage by herbivores, and fitness in nature. This gene encodes the first enzyme in the glucosinolate biosynthetic pathway, causing variation in chemical defense and herbivore damage, with subsequent effects on fitness. These ecological effects are driven by functional changes following gene duplication, and by two selectively favored amino acid changes in the proteins that they encode. These changes cause a gain of novel enzyme function, modulated by allelic differences in catalytic rate and gene copy number, which control survival and reproduction in nature.
Finally, to understand biochemical control of complex trait variation, we examined the relationship between pathway flux and protein polymorphism in the enzymes responsible for glucosinolate biosynthesis. We perturbed the enzymes in the glucosinolate pathway, and showed that flux control is focused in the first enzymatic step, and that flux control of these defensive phenotypes is robust across environmental treatments. Furthermore, signatures of selection showed that this enzyme is the only one in the pathway that shows evidence of selection. Our results support the hypothesis that natural selection preferentially acts on enzymes with high control over flux and phenotype.