Betts Matthew G, Hadley Adam S, Kress W John
Department of Forest Ecosystems and Society, Oregon State University, Corvallis, OR 97331; and
Department of Forest Ecosystems and Society, Oregon State University, Corvallis, OR 97331; and.
Proc Natl Acad Sci U S A. 2015 Mar 17;112(11):3433-8. doi: 10.1073/pnas.1419522112. Epub 2015 Mar 2.
Understanding the mechanisms enabling coevolution in complex mutualistic networks remains a central challenge in evolutionary biology. We show for the first time, to our knowledge, that a tropical plant species has the capacity to discriminate among floral visitors, investing in reproduction differentially across the pollinator community. After we standardized pollen quality in 223 aviary experiments, successful pollination of Heliconia tortuosa (measured as pollen tube abundance) occurred frequently when plants were visited by long-distance traplining hummingbird species with specialized bills (mean pollen tubes = 1.21 ± 0.12 SE) but was reduced 5.7 times when visited by straight-billed territorial birds (mean pollen tubes = 0.20 ± 0.074 SE) or insects. Our subsequent experiments revealed that plants use the nectar extraction capacity of tropical hummingbirds, a positive function of bill length, as a cue to turn on reproductively. Furthermore, we show that hummingbirds with long bills and high nectar extraction efficiency engaged in daily movements at broad spatial scales (∼1 km), but that territorial species moved only short distances (<100 m). Such pollinator recognition may therefore affect mate selection and maximize receipt of high-quality pollen from multiple parents. Although a diffuse pollinator network is implied, because all six species of hummingbirds carry pollen of H. tortuosa, only two species with specialized bills contribute meaningfully to its reproduction. We hypothesize that this pollinator filtering behavior constitutes a crucial mechanism facilitating coevolution in multispecies plant-pollinator networks. However, pollinator recognition also greatly reduces the number of realized pollinators, thereby rendering mutualistic networks more vulnerable to environmental change.
了解复杂互利网络中实现协同进化的机制仍然是进化生物学的核心挑战。据我们所知，我们首次表明一种热带植物物种有能力区分访花者，并在传粉者群落中对繁殖进行差异化投入。在我们对223次鸟舍实验中的花粉质量进行标准化后，当长嘴的远距离按固定路线觅食的蜂鸟物种访花时，曲折赫蕉（Heliconia tortuosa）的成功授粉（以花粉管数量衡量）频繁发生（平均花粉管数量 = 1.21 ± 0.12标准误），但当被直嘴的领地性鸟类（平均花粉管数量 = 0.20 ± 0.074标准误）或昆虫访花时，成功授粉次数减少了5.7倍。我们随后的实验表明，植物利用热带蜂鸟的花蜜提取能力（喙长的正函数）作为开启繁殖的线索。此外，我们表明喙长且花蜜提取效率高的蜂鸟在广阔的空间尺度（约1公里）上进行日常活动，而领地性物种仅移动较短距离（<100米）。因此，这种传粉者识别可能会影响配偶选择，并使从多个亲本接收高质量花粉的量最大化。尽管意味着存在一个分散的传粉者网络，因为所有六种蜂鸟都携带曲折赫蕉的花粉，但只有两种具有特殊喙的物种对其繁殖有显著贡献。我们假设这种传粉者筛选行为构成了促进多物种植物 - 传粉者网络协同进化的关键机制。然而，传粉者识别也大大减少了实际传粉者的数量，从而使互利网络更容易受到环境变化的影响。
