Selection on floral traits in hermaphroditic plants is determined by both male and female reproductive success. However, predictions regarding floral trait and mating system evolution are often based solely on female fitness. Selection via male fitness has the potential to affect the outcomes of floral evolution. In this study, we used paternity analysis to assess individual selfing rates and selection on floral traits via male and female fitness in an experimental population of Clarkia xantiana where pollen limitation of seed set was strong.
Results/Conclusions
We detected selection through both female and male fitness with reinforcing or non-interfering patterns of selection through the two sex functions. For female fitness, selection favored reduced herkogamy and protandry, traits which promote increased autonomous selfing. For male fitness, selection on petal area was disruptive with higher trait values conferring greater pollinator attraction and outcross siring success while smaller trait values led to higher selfed siring success. Combining both female and male fitness, selection on petal area and protandry was disruptive because intermediate phenotypes were less successful as both males and females. Finally, functional relationships among male and female fertility components indicated that selfing resulted in seed discounting and pollen discounting. Under these functional relationships, the evolutionarily stable selfing rate can be intermediate, or predominantly selfing or outcrossing, depending on the segregating load of deleterious mutations.