CAS Key Laboratory of Plant Diversity and Biogeography of East Asia, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, China.
College of Life Sciences, Shaanxi Normal University, Xi'an, China.
Plant Biol (Stuttg). 2024 Aug;26(5):665-674. doi: 10.1111/plb.13680. Epub 2024 Jun 27.
The flower perianth has various, non-mutually exclusive functions, such as visual signalling to pollinators and protecting the reproductive organs from the elements and from florivores, but how different perianth structures and their different sides play a role in these functions is unclear. Intriguingly, in many species there is a clear colour difference between the different sides of the perianth, with colour patterns or pigmentation present on only one side. Any adaptive benefit from such colour asymmetry is unclear, as is how the asymmetry evolved. In this viewpoint paper, we address the phenomenon of flowers with differently coloured inner and outer perianth sides, focusing on petals of erect flowers. Guided by existing literature and our own observations, we delineate three non-mutually exclusive evolutionary hypotheses that may explain the factors underlying differently coloured perianth sides. The pollen-protection hypothesis predicts that the outer side of petals contributes to protect pollen against UV radiation, especially during the bud stage. The herbivore-avoidance hypothesis predicts that the outer side of petals reduces the flower's visibility to herbivores. The signalling-to-pollinators hypothesis predicts that flower colours evolve to increase conspicuousness to pollinators. The pollen-protection hypothesis, the herbivore-avoidance hypothesis, and the signalling-to-pollinators hypothesis generate largely but not entirely overlapping predictions about the colour of the inner and outer side of the petals. Field and laboratory research is necessary to disentangle the main drivers and adaptive significance of inner-outer petal side colour asymmetry.
花被具有多种非互斥的功能，例如向传粉者发出视觉信号、保护生殖器官免受自然因素和食花动物的侵害，但不同的花被结构及其不同侧面在这些功能中扮演什么角色尚不清楚。有趣的是，在许多物种中，花被的不同侧面之间存在明显的颜色差异，只有一侧存在颜色图案或色素沉着。这种颜色不对称性的任何适应优势尚不清楚，其进化方式也不清楚。在这篇观点文章中，我们将重点讨论具有不同颜色内、外花被侧面的花朵现象，主要关注直立花朵的花瓣。在现有文献和我们自己观察的指导下，我们划定了三个非互斥的进化假设，这些假设可能解释了花被不同侧面颜色的潜在因素。花粉保护假说预测，花瓣的外侧面有助于保护花粉免受紫外线辐射的伤害，尤其是在花蕾期。食草动物回避假说预测，花瓣的外侧面降低了花朵对食草动物的可见度。向传粉者传递信号的假说预测，花朵的颜色会进化以增加对传粉者的显眼度。花粉保护假说、食草动物回避假说和向传粉者传递信号的假说对花瓣内、外侧的颜色产生了很大但并非完全重叠的预测。需要进行野外和实验室研究，以厘清内、外侧花瓣颜色不对称的主要驱动因素和适应意义。
