Floral design in Polemonium brandegei (polemoniaceae): Genetic and phenotypic variation under hawkmoth and hummingbird pollination

Many flowering plants reduce sexual interference between male and female functions through herkogamy, the spatial separation of anthers and stigmas. Many species are monomorphic and present stigmas either above or below the anthers, "approach" or "reverse" herkogamy, respectively. Although numerous studies have examined species that are polymorphic for approach and reverse herkogamy, species with continuous variation in sex organ position have received little attention. We examined continuous variation in anther position, style length, herkogamy, and flower shape in the self-sterile perennial herb Polemonium brandegei. We observed pollinators, measured flower shape and sex organ position in the field, and estimated heritabilities and genetic correlations among floral traits in the greenhouse. The two major pollinators were hummingbirds Selasphorus platycercus and hawkmoths Hyles lineata and Hyles gallii, which are believed to select for exserted and recessed sex organs, respectively. Herkogamy was not polymorphic but rather ranged continuously from reverse to approach, independent of corolla shape, size, and age. Corolla tube length and width, sex organ heights, and herkogamy were all heritable. Genetic variation for the spatial separation of stigmas and anthers was particularly high (h² = 0:851; CV_a = 36:88; CV_a is the coefficient of additive genetic variation). Temporal fluctuations in pollinator frequency likely maintain the variation in herkogamy by imposing heterogeneous selection on floral traits.