Pollination biology and secondary pollinators in seven North American Aquilegia species

Premise of research. The diversity of North American columbine species likely resulted from a radiation promoted by pollinators. Despite previous studies involving plant-pollinator interactions, pollinators have been documented for less than half the 25 North American species, and discussions of floral syndromes have focused on nectar-collecting pollinators. Methodology. We performed pollination fieldwork in the western United States and complementary studies on the living collections in the Botanical Garden of the University of Vienna, Austria. We report floral visitors, floral traits, anthesis patterns, and tests for stigmatic receptivity and/or self-pollination. Our aim was to contribute critical empirical data on the pollination biology of seven North American Aquilegia species displaying different floral syndromes, with particular attention to secondary pollinator activity. Pivotal results. Three species, A. brevistyla, A. flavescens, and A. laramiensis, are pollinated by pollen- and/or nectar-collecting bees. Aquilegia eximia and A. formosa exhibit mixed hummingbird-bee pollination systems. Aquilegia chrysantha is a generalist and pollinated by hawkmoths, hummingbirds, and pollen-collecting insects, whereas A. scopulorum possibly has a mixed hawkmoth-bee pollination system. All species were also visited by smaller bees, flies, and other occasional insects. Like other Aquilegia species, A. laramiensis appears to be self-fertile. Aquilegia chrysantha is partially protogynous, whereas preliminary results for A. formosa and A. eximia may indicate adichogamy. Conclusions. Coupled with previous studies, our observations confirm that North American Aquilegia species, despite their characterization into specific floral syndromes, are not always limited to a single pollinator type but are often visited by additional species or mixed communities of nectar- and pollen-collecting animals. The impact of the different pollinators on plant fitness remains to be tested.