Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario M5S 3G5, Canada.
Am Nat. 2010 Jun;175(6):717-26. doi: 10.1086/652473.
One floral characteristic associated with bat pollination (chiropterophily) is copious pollen production, a pattern we confirmed in a local comparison of hummingbird- and bat-adapted flowers from a cloud forest site in Ecuador. Previous authors have suggested that wasteful pollen transfer by bats accounted for the pattern. Here we propose and test a new hypothesis: bats select for increased pollen production because they can efficiently transfer larger amounts of pollen, which leads to a more linear male fitness gain curve for bat-pollinated plants. Flight cage experiments with artificial flowers and flowers of Aphelandra acanthus provide support for this hypothesis; in both instances, the amount of pollen delivered to stigmas by birds is not related to the amount of pollen removed from anthers on the previous visit, while the same function for bats increases linearly. Thus, increased pollen production will be linearly related to increased male reproductive success for bat flowers, while for bird flowers, increased pollen production leads to rapidly diminishing fitness returns. We speculate that fur takes up and holds more pollen than feathers, which seem to readily shed excess grains. Our gain-curve hypothesis may also explain why evolutionary shifts from bird to bat pollination seem more common than shifts in the opposite direction.
与蝙蝠授粉（chiropterophily）相关的一个花卉特征是大量花粉生产，我们在厄瓜多尔云雾森林的一个地点对适应蜂鸟和蝙蝠的花朵进行了本地比较，证实了这一模式。之前的作者认为，蝙蝠浪费花粉转移是造成这种模式的原因。在这里，我们提出并测试了一个新的假设：蝙蝠选择增加花粉生产，因为它们可以有效地转移更多的花粉，这导致了蝙蝠授粉植物的雄性适合度增益曲线更加线性。使用人工花和 Aphelandra acanthus 的花进行飞行笼实验为这一假设提供了支持；在这两种情况下，鸟类传递到柱头的花粉量与前一次访问中从花药中去除的花粉量无关，而对于蝙蝠来说，同一功能呈线性增加。因此，对于蝙蝠花来说，花粉产量的增加将与雄性生殖成功率的增加呈线性相关，而对于鸟花来说，花粉产量的增加会导致适合度回报迅速减少。我们推测，皮毛比羽毛吸收和保持更多的花粉，而羽毛似乎很容易脱落多余的花粉。我们的收益曲线假说也可以解释为什么从鸟类到蝙蝠授粉的进化转变似乎比相反方向的转变更为常见。
