Ayasse M, Schiestl F P, Paulus H F, Löfstedt C, Hansson B, Ibarra F, Francke W
Institute of Zoology, University of Vienna, Austria.
Evolution. 2000 Dec;54(6):1995-2006. doi: 10.1111/j.0014-3820.2000.tb01243.x.
The orchid Ophrys sphegodes Miller is pollinated by sexually excited males of the solitary bee Andrena nigroaenea, which are lured to the flowers by visual cues and volatile semiochemicals. In O. sphegodes, visits by pollinators are rare. Because of this low frequency of pollination, one would expect the evolution of strategies that increase the chance that males will visit more than one flower on the same plant; this would increase the number of pollination events on a plant and therefore the number of seeds produced. Using gas chromatography-mass spectrometry (GC-MS) analyses, we identified more than 100 compounds in the odor bouquets of labellum extracts from O. sphegodes; 24 compounds were found to be biologically active in male olfactory receptors based on gas chromatography with electroantennographic detection (GC-EAD). Gas chromatography (GC) analyses of odors from individual flowers showed less intraspecific variation in the odor bouquets of the biologically active compounds as compared to nonactive compounds. This can be explained by a higher selective pressure on the pollinator-attracting communication signal. Furthermore, we found a characteristic variation in the GC-EAD active esters and aldehydes among flowers of different stem positions within an inflorescence and in the n-alkanes and n-alkenes among plants from different populations. In our behavioral field tests, we showed that male bees learn the odor bouquets of individual flowers during mating attempts and recognize them in later encounters. Bees thereby avoid trying to mate with flowers they have visited previously, but do not avoid other flowers either of a different or the same plant. By varying the relative proportions of saturated esters and aldehydes between flowers of different stem positions, we demonstrated that a plant may take advantage of the learning abilities of the pollinators and influence flower visitation behavior. Sixty-seven percent of the males that visited one flower in an inflorescence returned to visit a second flower of the same inflorescence. However, geitonogamy is prevented and the likelihood of cross-fertilization is enhanced by the time required for the pollinium deposited on the pollinator to complete its bending movement, which is necessary for pollination to occur. Cross-fertilization is furthermore enhanced by the high degree of odor variation between plants. This variation minimizes learned avoidance of the flowers and increases the likelihood that a given pollinator would visit several to many different plants within a population.
兰花蜂兰（Ophrys sphegodes Miller）由独居蜂黑带地蜂（Andrena nigroaenea）性兴奋的雄性个体授粉，这些雄性个体被视觉线索和挥发性信息化学物质吸引到花朵上。在蜂兰中，传粉者的来访很罕见。由于授粉频率低，人们预计会进化出一些策略，以增加雄性个体访问同一植株上多朵花的机会；这将增加植株上的授粉事件数量，从而增加种子产量。通过气相色谱 - 质谱联用（GC - MS）分析，我们在蜂兰唇瓣提取物的气味组合中鉴定出100多种化合物；基于气相色谱 - 触角电位检测（GC - EAD），发现其中24种化合物对雄性嗅觉感受器具有生物活性。对单朵花气味的气相色谱（GC）分析表明，与无活性化合物相比，具有生物活性的化合物在气味组合中的种内变异较小。这可以通过对吸引传粉者的通讯信号有更高的选择压力来解释。此外，我们发现，在一个花序内不同茎位置的花朵之间，GC - EAD活性酯和醛存在特征性变异，不同种群的植株之间正构烷烃和烯烃也存在变异。在我们的野外行为测试中，我们表明雄性蜜蜂在交配尝试过程中学习单朵花的气味组合，并在后续相遇中识别它们。蜜蜂因此避免试图与它们之前访问过的花朵交配，但也不会避开同一植株或不同植株的其他花朵。通过改变不同茎位置花朵之间饱和酯和醛的相对比例，我们证明植物可以利用传粉者的学习能力并影响花朵访问行为。在一个花序中访问了一朵花的雄性个体中，67%会返回访问同一花序的第二朵花。然而，由于沉积在传粉者身上的花粉块完成弯曲运动所需的时间（这是授粉发生所必需的），自体受精被阻止，异花受精的可能性增加。此外，植株之间高度的气味变异也增强了异花受精。这种变异使对花朵的学习性回避最小化，并增加了给定传粉者在一个种群内访问几株到许多不同植株的可能性。
