Classical and 3-D pollination syndromes of Aquilegia

Flowers in the genus Aquilegia are pentamerous with two whorls of petaloid perianth organs. The organs differ greatly in shape (flat vs. spurred) and, in most species, also in colour. In Asia and Europe Aquilegia flowers are mostly pollinated by bumblebees and bees, while in North America shifts to hummingbirds and hawkmoths have occurred repeatedly. In earlier studies, typical bee, hummingbird or hawkmoth syndromes have been described for different Aquilegia species. However, as field observations have shown, Aquilegia flowers are almost always visited by a number of different pollen and nectar collectors, and some Aquilegia species seem to exhibit mixed pollination systems. In a first step, we established for each species its “classical” pollination syndrome (bee-humming-bird-hawkmoth) based on general floral traits such as perianth colour, spur length etc. In a second step, we also considered additional floral traits that are involved in the physical interaction between plant and pollinators such as position of the reproductive organs in relation to the whole flower, flower orientation etc. Furthermore, we distinguished between nectar- and pollen-collecting pollinators in our analyses. Finally, to better understand the floral evolution through pollinator-driven selection, we used X-ray computed tomography and identified additional, 3-dimensional shape traits possibly resulting from the adaptation to one or more types of pollinators.