On the nature of genetic variation in yellow monkeyflower (Mimulus guttatus): combining theoretical and empirical approaches

Evolution via natural selection requires standing variation in a population while simultaneously diminishing it at loci under selection, a paradox that continues to vex evolutionary biologists. The work presented here contributes to our understanding of how variation can be maintained by selection, why decreasing genetic variation is detrimental on an individual level, and how genetic variation can have complicated effects on fitness-related phenotypes. Chapter one demonstrates that antagonistic pleiotropy caused by a fitness tradeoff between polygenic traits can maintain variation at a single locus by generating emergent overdominance. The results are surprisingly robust to perturbations in the underlying assumptions about random mating and environmental heterogeneity. Chapter two provides an explanation for how mating system can influence the maintenance of variation. Inbreeding depression in the Iron Mountain population of yellow monkeyflower (Mimulus guttatus) is potentially severe enough to maintain outcrossing and is also predicted by the load of rare alleles carried by a genotype. Chapter three illustrates the complex relationships between genotype and phenotype that are likely underappreciated in typical QTL mapping or GWAS approaches, due to tightly linked antagonistic effectors. It provides a mechanism for studying the influence of genetic variation on complex fitness-related phenotypes, like flower size