What can genome-wide association studies tell us about the evolutionary forces maintaining genetic variation for quantitative traits?

Understanding the evolutionary forces that shape genetic variation within species has long been a goal of evolutionary biology. Integrating data for the genetic architecture of traits from genome-wide association mapping studies (GWAS) along with the development of new population genetic methods for identifying selection in sequence data may allow us to evaluate the roles of mutation–selection balance and balancing selection in shaping genetic variation at various scales. Here,wereview the theoretical predictions for genetic architecture and additional signals of selection on genomic sequence for the loci that affect traits. Next,we reviewhow plant GWAS have tested for the signatures of various selective scenarios. Limited evidence to date suggests that within-population variation is maintained primarily by mutation–selection balance while variation across the landscape is the result of local adaptation. However, there are a number of inherent biases in these interpretations. We highlight these challenges and suggest ways forward to further understanding of the maintenance of variation.