Center for Ecological Research, Kyoto University, Otsu, Shiga, Japan.
Graduate School of Science, Kyoto University, Kitashirakawa-Oiwake-cho, Sakyo, Kyoto, Japan.
Ann Bot. 2021 Jan 7;127(2):231-239. doi: 10.1093/aob/mcaa168.
The great diversity of floral characteristics among animal-pollinated plants is commonly understood to be the result of coevolutionary interactions between plants and pollinators. Floral antagonists, such as nectar thieves, also have the potential to exert an influence upon the selection of floral characteristics, but adaptation against floral antagonists has attracted comparatively little attention. We found that the corollas of hornet-pollinated Codonopsis lanceolata (Campanulaceae) and the tepals of bee-pollinated Fritillaria koidzumiana (Liliaceae) are slippery to nectar-thieving ants living in the plant's habitat; because the flowers of both species have exposed nectaries, slippery perianths may function as a defence against nectar-thieving ants.
We conducted a behavioural experiment and observed perianth surface microstructure by scanning electron microscopy to investigate the mechanism of slipperiness. Field experiments were conducted to test whether slippery perianths prevent floral entry by ants, and whether ant presence inside flowers affects pollination.
Scanning electron microscopy observations indicated that the slippery surfaces were coated with epicuticular wax crystals. The perianths lost their slipperiness when wiped with hexane. Artificial bridging of the slippery surfaces using non-slippery materials allowed ants to enter flowers more frequently. Experimental introduction of live ants to the Codonopsis flowers evicted hornet pollinators and shortened the duration of pollinator visits. However, no statistical differences were found in the fruit or seed sets of flowers with and without ants.
Slippery perianths, most probably based on epicuticular wax crystals, prevent floral entry by ants that negatively affect pollinator behaviour. Experimental evidence of floral defence based on slippery surfaces is rare, but such a mode of defence may be widespread amongst flowering plants.
动物传粉植物的花部特征具有多样性，通常被认为是植物与传粉者协同进化相互作用的结果。花蜜盗食者等花部拮抗物也有可能对花部特征的选择施加影响，但针对花部拮抗物的适应性进化却很少受到关注。我们发现，长距风铃草（桔梗科）的喇叭状花冠和延龄草（百合科）的片状花被对生活在其栖息地的盗蜜蚂蚁具有疏水性；由于这两个物种的花朵均具有暴露的蜜腺，疏水性的花被可能起到抵御盗蜜蚂蚁的作用。
我们通过行为实验和扫描电子显微镜观察花被表面微观结构来研究疏水性的产生机制。我们还进行了野外实验，以检验疏水性花被是否能阻止蚂蚁进入花朵，以及蚂蚁在花朵内的存在是否会影响传粉。
扫描电子显微镜观察表明，疏水性表面覆盖有表皮蜡质晶体。用己烷擦拭花被会使其失去疏水性。使用非疏水性材料人为桥接疏水性表面会使蚂蚁更频繁地进入花朵。将活体蚂蚁引入风铃草花朵中会驱逐胡蜂传粉者，并缩短传粉者访问花朵的时间。然而，有蚂蚁和无蚂蚁的花朵在果实和种子设置方面没有统计学差异。
可能基于表皮蜡质晶体的疏水性花被阻止了对传粉者行为产生负面影响的蚂蚁进入花朵。基于疏水性表面的花部防御的实验证据很少见，但这种防御模式可能在开花植物中广泛存在。
