Populations with greater flexibility in floral traits modify mating system in response to the pollinator environment

1. Mixed mating and variation in outcrossing rate among populations of the same species are common. Outcrossing can be affected by pollinator activity and floral traits that facilitate or impede autonomous self-fertilization. However, the relative contribution of pollen limitation and evolved differences in the ability to self fertilize to variation in the mating system is poorly understood and can only be disentangled using an experimental approach. 2. We placed arrays of plants from eight Campanula americana populations that varied in autonomous selfing ability (hereafter \"autonomy\") in sun and shade habitats to create high- and low-pollination environments. Floral visitors were observed and pollen limitation, dichogamy, herkogamy, and pollen persistence within the flower were measured. Outcrossing rate was estimated for a subset of the arrays. 3. Pollen limitation was over three-times higher in the shade than the sun due to differences in pollinator visitation. Populations with high ...