Genetic variation within populations provides the raw material for adaptive divergence between populations and species, and understanding the fitness consequences of such variation is a major goal of evolutionary biology. Here, we explore correlations among floral traits, individual selfing rates and female fitness within a wild population of the primarily outcrossing plant Mimulus guttatus. Previous work has shown that floral variation in this population is highly heritable and not primarily due to deleterious mutations at low frequency. Small flowers and high selfing rates have evolved several times in closely related members of the M. guttatus species complex, potentially to assure reproduction under conditions of pollen limitation. On the other hand, phenotypic measures of selection typically find positive relationships between floral size characters and fitness. In this study, we used a combination of experimental manipulations and molecular marker-based paternity analysis to tease apart the complex functional relationships among floral characters, self-fertilization and fitness in the field. We address the following questions: Is there pollen limitation of female fitness and, if so, does it vary with floral morphology? Is individual variation in floral traits (corolla size, stigma-anther separation) correlated with selfing rate? With fitness? What ecological or genetic factors generate such correlations? These results complement our growing understanding of the genetic basis of mating system divergence within the Mimulus guttatus complex.

Key words: floral variation, Mimulus guttatus, phenotypic selection, selfing rate