J Plant Ecol ›› 2020, Vol. 13 ›› Issue (3): 354-360.DOI: 10.1093/jpe/rtaa023

• Research Articles • Previous Articles     Next Articles

The ultraviolet colour component enhances the attractiveness of red flowers of a bee-pollinated plant

Zhe Chen1,2, Chang-Qiu Liu3, Hang Sun1, * and Yang Niu1, *   

  1. 1 CAS Key Laboratory for Plant Diversity and Biogeography of East Asia, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650201, Yunnan, China, 2 University of Chinese Academy of Sciences, Beijing 100049, China, 3 Center for Gardens and Horticultural Studies, Guangxi Institute of Botany, Chinese Academy of Sciences, Guilin 541006, Guangxi, China

    *Corresponding author. E-mail: niuyang@mail.kib.ac.cn (Y.N.); sunhang@mail.kib.ac.cn (H.S.)
  • Received:2020-02-22 Revised:2020-04-21 Accepted:2020-05-22 Online:2020-05-25 Published:2020-06-01

Abstract:

Aims

Bee-pollinated flowers are rarely red, presumably because bees (which lack red receptors) have difficulty detecting red targets. Although the response of bees to red colour has been investigated in lab experiments, most stimuli have been pure red, while the subtle diversity of red as perceived by humans (human-red) has received very limited attention. Here we test the hypothesis that ultraviolet (UV) reflected from human-red flowers enhances their attractiveness to bees, through increased chromatic contrast.

Methods

Using Onosma confertum (Boraginaceae), a plant with UV-reflecting red flowers that are pollinated by bumblebees, we investigated the effects of UV reflection on pollinator responses by conducting phenotypic manipulation experiments in the field. Colour preferences of flower-naïve bumblebees were also examined. Colour perception by bumblebees was estimated in terms of chromatic and achromatic contrast, based on two different colour perception models.

Important Findings

We found that both natural and flower-naïve bumblebees strongly preferred visiting UV-reflecting targets compared with UV-absorbing ones. Colour models show that the UV-reflecting flowers exhibit higher spectral purity and higher chromatic contrast against the foliage background, whereas they have similar achromatic contrast in terms of green receptor contrast. These results indicate that the component of UV reflection increases chromatic contrast in O. confertum, enhancing the visual attractiveness of these red flowers to bumblebees. We further infer that the secondary reflectance might be a necessary component in human-red flowers that are primarily pollinated by animals without red receptors, such as bees.

Key words: bee pollination, colour vision, floral colour evolution, pollination syndrome, red flower, UV reflection

摘要:

蜂媒花很少呈红色,这可能是由于蜂类的眼睛缺少红光受体,因而较难搜寻红色目标。尽管有实验研究过蜂类对红色的反应,但所用目标多为纯红色。而人类感受到的红色中其实包含细微的色调差别,这些差别还甚少受到关注。我们在本研究中检验了如下假说:红花中的紫外反射组分能够增加其彩调反差,因而增强其对蜂类的吸引力。紫草科的密花滇紫草(Onosma confertum)由熊蜂传粉,其花为红色,但紫外反射明显。本研究利用该植物设计了表型操控实验,在野外检验了紫外反射对传粉者访花行为的影响。我们还在受控环境下检验了无经验熊蜂的色彩偏好。利用两个色彩模型评估熊蜂的色彩感受,用彩调反差和明度反差两个参数进行估计。研究发现,自然状态下及无经验的饲养熊蜂均偏好访问具有紫外反射的红色目标。色彩模型分析表明,具紫外反射的红花对蜂而言色彩更纯,且与叶片背景的彩调反差更大;而它们与无紫外反射的红花在明度反差方面(以绿光受体的反差估计)表现相似。这些结果表明,密花滇紫草红色花朵中的紫外反射组分增加了其彩调反差,增强了其对熊蜂的吸引力。我们推测,由于某些传粉者(例如蜂类)无红光受体,对由它们传粉的红色花而言,光谱中的副反射特征(例如紫外反射)可能是其花色中的必要组分。

关键词: 蜂媒, 色觉, 花色演化, 传粉综合征, 红色花, 紫外反射