Eilers Elisabeth J, Kleine Sandra, Eckert Silvia, Waldherr Simon, Müller Caroline
Chemical Ecology, Bielefeld University, Bielefeld, Germany.
Biodiversity Research/Systematic Botany, University of Potsdam, Potsdam, Germany.
Front Plant Sci. 2021 Jan 20;11:611877. doi: 10.3389/fpls.2020.611877. eCollection 2020.
Floral volatiles and reward traits are major drivers for the behavior of mutualistic as well as antagonistic flower visitors, i.e., pollinators and florivores. These floral traits differ tremendously between species, but intraspecific differences and their consequences on organism interactions remain largely unknown. Floral volatile compounds, such as terpenoids, function as cues to advertise rewards to pollinators, but should at the same time also repel florivores. The reward composition, e.g., protein and lipid contents in pollen, differs between individuals of distinct plant families. Whether the nutritional value of rewards within the same plant species is linked to their chemotypes, which differ in their pattern of specialized metabolites, has yet not been investigated. In the present study, we compared plants of five terpenoid chemotypes with regard to flower production, floral headspace volatiles, pollen macronutrient and terpenoid content, and floral attractiveness to florivorous beetles. Our analyses revealed remarkable differences between the chemotypes in the amount and diameter of flower heads, duration of bloom period, and pollen nutritional quality. The floral headspace composition of pollen-producing mature flowers, but not of premature flowers, was correlated to that of pollen and leaves in the same plant individual. For two chemotypes, florivorous beetles discriminated between the scent of mature and premature flower heads and preferred the latter. In semi-field experiments, the abundance of florivorous beetles and flower tissue miners differed between chemotypes. Moreover, the scent environment affected the choice and beetles were more abundant in homogenous plots composed of one single chemotype than in plots with different neighboring chemotypes. In conclusion, flower production, floral metabolic composition and pollen quality varied to a remarkable extend within the species , and the attractiveness of floral scent differed also intra-individually with floral ontogeny. We found evidence for a trade-off between pollen lipid content and pollen amount on a per-plant-level. Our study highlights that chemotypes which are more susceptible to florivory are less attacked when they grow in the neighborhood of other chemotypes and thus gain a benefit from high overall chemodiversity.
花香挥发物和报酬特性是互利性以及对抗性访花者（即传粉者和食花动物）行为的主要驱动因素。这些花的特性在物种间差异极大，但种内差异及其对生物相互作用的影响在很大程度上仍不为人知。花香挥发化合物，如萜类化合物，作为向传粉者宣传报酬的信号，但同时也应排斥食花动物。报酬组成，例如花粉中的蛋白质和脂质含量，在不同植物科的个体间存在差异。同一植物物种内报酬的营养价值是否与其化学型相关，而这些化学型在其特殊代谢产物模式上有所不同，尚未得到研究。在本研究中，我们比较了五种萜类化学型的植物在花的产量、花的顶空挥发物、花粉常量营养素和萜类含量以及对食花甲虫的花的吸引力方面的差异。我们的分析揭示了化学型在花头的数量和直径、花期持续时间以及花粉营养质量方面存在显著差异。产生花粉的成熟花的花顶空成分，而非未成熟花的，与同一植株个体的花粉和叶子的花顶空成分相关。对于两种化学型，食花甲虫能够区分成熟花头和未成熟花头的气味，并更喜欢后者。在半田间实验中，食花甲虫和花组织矿工的数量在不同化学型之间存在差异。此外，气味环境影响了选择，并且在由单一化学型组成的同质地块中甲虫比在有不同相邻化学型的地块中更为丰富。总之，花的产量、花的代谢组成和花粉质量在物种内有显著变化，并且花香的吸引力在个体内也随花的发育而不同。我们发现了在单株水平上花粉脂质含量和花粉数量之间权衡的证据。我们的研究强调，更容易受到食花动物侵害的化学型在与其他化学型相邻生长时受到的攻击较少，因此从高总体化学多样性中获益。
