动物授粉植物之间的花卉特征差异很大,通常被认为是植物与传粉者之间共同进化相互作用的结果。花卉拮抗剂,比如盗花蜜贼,也有可能对花卉特性的选择产生影响,但是对花卉拮抗剂的适应吸引了相对较少的关注。我们发现,大黄蜂授粉的党参(Campanulaceae)的花冠和蜜蜂授粉的贝母(百合科)的花被滑到生活在植物栖息地的采蜜蚂蚁;因为这两个物种的花朵都有裸露的蜜腺,光滑的花被可能起到防御花蜜盗窃蚂蚁的作用。
我们进行了行为实验,并通过扫描电子显微镜观察了花被表面的微观结构,以研究光滑的机理。进行了田间试验,以测试光滑的花被是否可以防止蚂蚁进入花朵,以及蚂蚁在花内的存在是否会影响授粉。
扫描电子显微镜观察表明,光滑表面涂有表皮蜡晶体。用己烷擦拭时,花被失去了滑溜性。使用防滑材料人工桥接光滑的表面,使蚂蚁可以更频繁地进入花朵。将活蚂蚁实验性地引入党参花驱逐了大黄蜂传粉者,并缩短了传粉者访问的时间。然而,有和没有蚂蚁的花的果实或种子没有发现统计学差异。
光滑的花被,很可能是基于表皮蜡晶体,防止蚂蚁进入花卉,对传粉者的行为产生负面影响。基于光滑表面的花卉防御的实验证据很少,但是这种防御方式可能在开花植物中很普遍。
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.