College of Horticulture & Forestry Sciences/Hubei Engineering Technology Research Center for Forestry Information, Huazhong Agricultural University, Wuhan, China.
Institute of Wetland Research, Chinese Academy of Forestry, Beijing, China.
Plant Biol (Stuttg). 2021 Jan;23(1):156-161. doi: 10.1111/plb.13197. Epub 2020 Nov 27.
Floral traits are recognized to have evolved under selection for abiotic and biotic factors. Complex zygomorphic flowers usually face horizontally. It has been proved that a horizontal orientation facilitates pollinator recognition and pollination efficiency, but its significance in adaptation to abiotic factors remains unknown. The floral orientation of Abelia × grandiflora naturally varies around horizontal (with an angle of -30 to +33° between the floral main axis and the horizontal). We examined whether three different floral orientations affected flower thermal conditions, response to rain and pollination. Results showed that floral orientation had no effect on diurnal variations in flower temperature. The anthers of all three flower orientations were wetted by rainfall, but the inclined upward-facing flowers contained significantly more rainwater. The horizontal flowers received significantly higher visitation by hawkmoths and had a higher stigmatic pollen load. In contrast, the upward flower orientation reduced pollination precision, while downward-facing flowers had decreased pollinator attraction. This study indicates that horizontal flowers may have evolved as a trade-off between rain protection and pollination. Zygomorphic flowers that deviate from a horizontal orientation may have lower fitness because of flower flooding by rainwater and decreased pollen transfer.
花部特征被认为是在非生物和生物因素的选择下进化而来的。复杂的左右对称花通常是水平朝向的。已经证明，水平方向有利于传粉者的识别和传粉效率，但它在适应非生物因素方面的意义尚不清楚。ABELIA×GRANDIFLORA 的花部朝向自然在水平方向上变化（花主轴和水平方向之间的角度为-30 至+33°）。我们研究了三种不同的花部朝向是否会影响花部的热条件、对雨水的响应和传粉。结果表明，花部朝向对花部温度的日变化没有影响。三种花部朝向的花药都被雨水打湿，但向上倾斜的花部含有明显更多的雨水。水平花部吸引的天蛾访问量明显更高，柱头的花粉负荷也更高。相比之下，向上的花部朝向降低了传粉的精确性，而下垂的花部则降低了传粉者的吸引力。本研究表明，水平花部可能是在避雨和传粉之间的权衡中进化而来的。偏离水平方向的左右对称花可能因为被雨水淹没和花粉转移减少而具有较低的适合度。
