Experimental analysis of protogyny in Aquilegia canadensis (Ranunculaceae)

Dichogamy is very common in flowering plants and is widely thought to reduc e pollen-pistil interference, especially self-pollination. Yet. the functio nal significance of dichogamy has rarely been studied. We investigated the nature and functioning of dichogamy in eastern Ontario populations of Aquil egia canadensis, a highly selfing columbine previously described as protogy nous. We then manipulated flowers to determine whether increased protogyny would reduce self-fertilization. Contrary to previous reports, A. canadensi s is not dichogamous. Controlled pollinations in a greenhouse showed that p ollen tubes generally begin to develop after anther dehiscence. Although st igmas can collect pollen early in floral development, naturally pollinated flowers collected from four populations had few pollen grains on stigmas an d almost no pollen tubes in styles until after anther dehiscence. Limited p ollen deposition before anther dehiscence was also associated with low nect ar availability and limited sepal expansion. Because inbreeding depression is strong in this species, selection may favor increased protogyny if it re duces selfing. We tested this hypothesis by comparing the level of selfing in flowers rendered protogynous by the removal of the first 19 (of 39) anth ers to develop, with nonprotogynous control flowers. Contrary to expectatio ns, protogyny did not reduce selfing. Our results emphasize the importance of detailed field observations and manipulative experiments in understandin g the nature and functional significance of dichogamy.