Floral variation in the generalist perennial herb Paeonia broteroi (Paeoniaceae): differences between regions with different pollinators and herbivores

This paper investigates the differences in floral phenotype in Paeonia broteroi (Paeoniaceae) in four populations at two distant mountainous regions in southern Spain. Paeonia broteroi flowers exhibit traits of a highly generalized pollination system, but previous studies have revealed that not all flower visitors are effective at pollen delivery. Plants differed between regions in the number of flowers per plant, petal size, number of stamens per flower, and ovules per carpel. Differences between regions could not be attributable to differences in the size structure of the plants. Flower visitors in the two regions differed in assemblage and body size at all the spatiotemporal scales. Larger visitors were more effective as pollinators in the region with the largest and more rewarding (as measured by the number of stamens) flowers, suggesting that pollinators may create opportunities for selection of certain floral traits. In contrast, the two regions did not differ in the probability of damage by herbivores, which did not select flowers based on any of the measured traits, nor affected maternal fecundity. Despite the differences in flower phenotype, potential maternal fecundity, and pollinator effectiveness, plants did not differ between regions in seed production. The role of pollinators as determinants of the differences between regions in floral phenotype, through male and female reproductive success, is discussed. Also, alternative explanations to divergence are addressed, with special reference to the patterns of resource allocation between sexual functions and genetic drift.