Within the genus Mimulus, predominantly selfing species tend to be found in habitats where water is ephemeral and outcrossing taxa where water is more persistent. Populations of Mimulus guttatus also inhabit sites that vary in the persistence of soil moisture. Individual allocation to sexual reproduction and vegetative propagation varies among populations in concert with local patterns of water persistence. Mating system may vary among these ecologically differentiated populations. Selection for reproductive assurance is likely to be greater in populations that experience ephemeral soil moisture and reproduce only through seed. In addition the plastic response to water of traits that influence mating system and reproductive assurance, is predicted to vary among populations that differ in water availability. I found that water availability influences flower size and pollen and ovule production under greenhouse conditions. In addition, autofertility and the distance between the anthers and the stigma vary with moisture level. While these traits vary among populations, their change in response to water availability is similar. These results suggest that environmental variation influences mating system and autofertility in Mimulus guttatus. In addition, populations appear to retain the ability to make similar adjustments to environmental variables despite underlying divergent reproductive patterns.

Key words: autofertility, floral traits, mating system, Mimulus guttatus, phenotypic plasticity