Pollinator-mediated selection on flowering phenology and floral display in a distylous herb Primula alpicola

The targets and causes of phenotypic selection are crucial to understanding evolutionary ecology. However, few studies have examined selection quantitatively from multiple sources on the same trait identified the agent of natural selection experimentally. Here we quantified phenotypic selection on traits, including flowering phenology and aspects of floral display via female fitness, in the distylous perennial herb Primula alpicola. To determine the role of pollinators in generating selection effects on floral traits, we compared the phenotypic selection gradients in open-pollinated and hand-pollinated plants. Our results show that pollinator-mediated linear selection on flowering start and correlational selection on the number of flowers and scape height explains most of the net phenotypic selection on these traits suggesting pollinators played an important role in shaping floral diversity. We used path analysis and structural equation modeling (SEM) to examine how herbivores affected the relationship between floral traits and female fitness, but no significant selection was caused by seed predators. These results suggest pollinators, not herbivores maybe the significant agent of selection on flora traits.