Department of Biology, Queen's University, Kingston, Ontario, Canada K7L 3N6.
Am J Bot. 2000 Sep;87(9):1246-56.
Dichogamy is very common in flowering plants and is widely thought to reduce pollen-pistil interference, especially self-pollination. Yet, the functional significance of dichogamy has rarely been studied. We investigated the nature and functioning of dichogamy in eastern Ontario populations of Aquilegia canadensis, a highly selfing columbine previously described as protogynous. We then manipulated flowers to determine whether increased protogyny would reduce self-fertilization. Contrary to previous reports, A. canadensis is not dichogamous. Controlled pollinations in a greenhouse showed that pollen tubes generally begin to develop after anther dehiscence. Although stigmas can collect pollen early in floral development, naturally pollinated flowers collected from four populations had few pollen grains on stigmas and almost no pollen tubes in styles until after anther dehiscence. Limited pollen deposition before anther dehiscence was also associated with low nectar availability and limited sepal expansion. Because inbreeding depression is strong in this species, selection may favor increased protogyny if it reduces selfing. We tested this hypothesis by comparing the level of selfing in flowers rendered protogynous by the removal of the first 19 (of 39) anthers to develop, with nonprotogynous control flowers. Contrary to expectations, protogyny did not reduce selfing. Our results emphasize the importance of detailed field observations and manipulative experiments in understanding the nature and functional significance of dichogamy.
雌雄异熟在开花植物中非常普遍，被广泛认为可以减少花粉-柱头干扰，尤其是自交。然而，雌雄异熟的功能意义很少被研究。我们研究了安大略省东部 Aquilegia canadensis 种群的雌雄异熟的性质和功能，这是一种高度自交的耧斗菜，以前被描述为雌先型。然后，我们操纵花朵以确定增加雌先型是否会减少自交。与之前的报道相反，A. canadensis 不是雌雄异熟的。温室中的控制授粉表明，花粉管通常在花药开裂后开始发育。尽管柱头在花发育的早期可以收集花粉，但从四个种群自然授粉的花朵的柱头花粉粒很少，在花药开裂后几乎没有花粉管在花柱中。在花药开裂之前，有限的花粉沉积也与花蜜供应有限和萼片扩张有限有关。由于在这个物种中近亲繁殖衰退很强，因此如果它减少自交，选择可能有利于增加雌先型。我们通过比较去除前 19 个（39 个中的 19 个）发育中的花药的花朵的自交程度与非雌先型对照花朵，来测试这个假设。出乎意料的是，雌先型并没有减少自交。我们的结果强调了在理解雌雄异熟的性质和功能意义时进行详细的野外观察和操纵实验的重要性。
