Muchhala Nathan
Department of Biology, University of Miami, Miami, Florida 33143, USA.
Am Nat. 2007 Apr;169(4):494-504. doi: 10.1086/512047. Epub 2007 Feb 5.
Evolution toward increased specificity in pollination systems is thought to have played a central role in the diversification of angiosperms. Theory predicts that the presence of trade-offs in adapting to different pollinator types will favor specialization, yet few studies have attempted to characterize such interactions in nature. I conducted flight cage experiments with bats, hummingbirds, and artificial flowers to examine effects of corolla width on pollination. I videotaped visits to analyze pollinator behavior and counted pollen grains transferred to stigmas. Results demonstrated that flower-pollinator fit is critical to effective pollination; wide corollas guided bat snouts better, and narrow corollas guided hummingbird bills better. Poor fit resulted in variable entry angles and decreased pollen transfer. A model using these results predicts that wide corollas will be selected for when bats make more than 44% of the visits and narrow corollas when they make fewer. Intermediate corollas are never favored (i.e., generalization is always suboptimal). This is the first study to clearly document a pollinator-mediated fitness trade-off in floral morphology.
授粉系统向更高特异性的进化被认为在被子植物的多样化过程中发挥了核心作用。理论预测，在适应不同传粉者类型时存在权衡取舍将有利于特化，但很少有研究试图描述自然界中的这种相互作用。我用蝙蝠、蜂鸟和人造花进行了飞行笼实验，以研究花冠宽度对授粉的影响。我拍摄访问过程以分析传粉者行为，并统计转移到柱头上的花粉粒数量。结果表明，花与传粉者的匹配对有效授粉至关重要；宽花冠能更好地引导蝙蝠的口鼻，窄花冠能更好地引导蜂鸟的喙。匹配不佳会导致进入角度可变并减少花粉转移。使用这些结果的一个模型预测，当蝙蝠的访问次数超过44%时，将选择宽花冠，而当蝙蝠的访问次数较少时，则选择窄花冠。中间花冠永远不会受到青睐（即，泛化总是次优的）。这是第一项明确记录传粉者介导的花形态适应性权衡的研究。
