Variation and Selection of Genes Controlling Ecologically Important Traits in Nature

Amidst the prevalence of studies on balancing selection or deleterious polymorphism, the relative importance of these evolutionary processes for phenotypic variation is unclear. To understand the evolutionary forces that influence complex trait variation in a wild relative of Arabidopsis, we cloned an ecologically important QTL in natural populations of Boechera stricta and measured the fitness of alleles in the populations where they evolved. Field measurements of selection indicate that this polymorphism is influenced by spatially heterogeneous natural selection. Next, we examined the relationship between flux and polymorphism in this pathway, showing that flux control is focused in the first enzymatic step, encoded by a gene experiencing selective diversification in several related species. Finally, to identify the genes and alleles responsible for ecologically important trait variation in nature, we are conducting a Genome-Wide Association Study (GWAS) on a panel of reference genotypes from 350 populations across the species range. For these accessions we assess the genetic variation from genome-wide resequencing and genotyping by sequencing, and associate these with trait variation for defensive chemistry, resistance to multiple herbivores, flowering time, and complex traits evaluated in the lab and the field. Implications for ecological genomics will be discussed.