DIFFERENTIATION OF FLORAL TRAITS ASSOCIATED WITH POLLINATOR PREFERENCE IN A GENERALIST-POLLINATED HERB, TROLLIUS RANUNCULOIDES (RANUNCULACEAE)

Premise of research. In flowers that are specialized, floral traits often differentiate in association with pollinator shifts. However, in species of generalized pollination, the role of pollinators in local population differentiation of floral traits is difficult to test. A crucial line of evidence is to contrast the direction and strength of pollinator selection among populations. Methodology. Variation in floral traits and pollinator assemblages was investigated in two populations of a generalist-pollinated herb, Trollius ranunculoides (Ranunculaceae), to detect the potential role of pollinators in floral differentiation. Pivotal results. The alpine population was visited more by flies, and the subalpine population was visited more by bees. Flower manipulations suggested that large flowers were more attractive to both bees and flies, while more petals were favored only by nectar-feeding flies. Compared to the subalpine population, plants in the alpine population had more petals per flower but smaller flowers where flies were predominant pollinators. Flower differences appeared to be genetically maintained in a common garden. Phenotypic selection analysis indicated stronger selection on petal number in the alpine population and oppositely more intense selection on flower diameter in the subalpine population, in accordance with the preferences of local pollinator assemblages. Conclusions. Heritability in floral traits, differences in local pollinator assemblages, and corresponding differences in phenotypic selection are together consistent with the view of pollinator-mediated selection on floral differentiation in T. ranunculoides.