A statistical Test for Floral Syndromes in Aquilegia (Ranunculacae)

Aquilegia flowers provide nectar to their pollinators via spurs that differ in length among species. In addition, flowers vary in colour, orientation, and to some extent also in shape. Traditionally, Aquilegia flowers have been classified into three floral syndromes associated to bee, hummingbird, or hawkmoth pollination. In Asia and Europe, Aquilegia species are mostly pollinated by bumble bees and bees, while in North America, shifts from the likely ancestral bee-pollination to pollination by hummingbirds and hawkmoths have occurred repeatedly. However, these syndromes were never statistically tested using data based on pollination studies. In addition, field observations have shown that 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. Here we use multivariate statistics, morphospaces, and random forest analyses to test for the association among floral traits (e.g. perianth colour, spur length, flower orientation) and pollinators (bumble bee, hummingbird, hawkmoth) in c. 30 species with documented pollinator observations. Although some groups are still poorly represented due to a lack of empirical pollination data, this allows us to statistically describe floral syndromes in Aquilegia, distinguishing between nectar- and pollen-collecting pollinators. We finally test whether mixed pollination systems (more than one primary pollinator) display their own floral syndromes or fall into one of the three main syndromes in Aquilegia.