CAS Key Laboratory for Plant Diversity and Biogeography of East Asia, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, Yunnan, China.
University of Chinese Academy of Sciences, Beijing, China.
Ann Bot. 2020 Oct 6;126(5):837-848. doi: 10.1093/aob/mcaa103.
Floral colour is a primary signal in plant-pollinator interactions. The association between red flowers and bird pollination is well known, explained by the 'bee avoidance' and 'bird attraction' hypotheses. Nevertheless, the relative importance of these two hypotheses has rarely been investigated on a large scale, even in terms of colour perception per se.
We collected reflectance spectra for 130 red flower species from different continents and ascertained their pollination systems. The spectra were analysed using colour vision models for bees and (three types of) birds, to estimate colour perception by these pollinators. The differences in colour conspicuousness (chromatic and achromatic contrast, purity) and in spectral properties between pollination systems and across continents were analysed.
Compared with other floral colours, red flowers are very conspicuous to birds and much less conspicuous to bees. The red flowers pollinated by bees and by birds are more conspicuous to their respective pollinators. Compared with the bird flowers in the Old World, the New World ones are less conspicuous to bees and may be more conspicuous not only to violet-sensitive but also to ultraviolet-sensitive birds. These differences can be explained by the different properties of the secondary reflectance peak (SP). SP intensity is higher in red flowers pollinated by bees than those pollinated by birds (especially New World bird flowers). A transition from high SP to low SP in red flowers can induce chromatic contrast changes, with a greater effect on reducing attraction to bees than enhancing attraction to birds.
Shades of red flowers differ between pollination systems. Moreover, red bird flowers are more specialized in the New World than in the Old World. The evolution towards colour specialization is more likely to result in higher efficiency of bee avoidance than bird attraction.
花色是植物-传粉者相互作用的主要信号。红花与鸟类传粉的关系众所周知，这可以用“蜜蜂回避”和“鸟类吸引”假说来解释。然而，即使就颜色感知本身而言，这两个假说的相对重要性也很少在大规模范围内得到调查。
我们从不同大陆收集了 130 种红花的反射光谱，并确定了它们的传粉系统。使用蜜蜂和（三种类型的）鸟类的颜色视觉模型对光谱进行分析，以估计这些传粉者的颜色感知。分析了不同传粉系统和不同大陆之间颜色显著性（颜色和非颜色对比、纯度）和光谱特性的差异。
与其他花色相比，红花对鸟类非常显著，对蜜蜂则不那么显著。蜜蜂和鸟类传粉的红花对各自的传粉者更为显著。与旧大陆的鸟类花相比，新大陆的鸟类花对蜜蜂的显著性较低，对不仅对紫敏鸟类而且对紫外敏鸟类可能更显著。这些差异可以用二次反射峰（SP）的不同特性来解释。蜜蜂传粉的红花的 SP 强度高于鸟类传粉的红花（尤其是新大陆的鸟类花）。在蜜蜂传粉的红花中，从高 SP 到低 SP 的转变会引起颜色对比的变化，对减少对蜜蜂的吸引力比对增强对鸟类的吸引力的影响更大。
传粉系统之间的红花色调不同。此外，新大陆的鸟类红花比旧大陆的更为专业化。向颜色专业化的进化更有可能导致蜜蜂回避效率的提高，而不是鸟类吸引效率的提高。
