Nepi Massimo, Grasso Donato A, Mancuso Stefano
Department of Life Sciences, University of Siena, Siena, Italy.
Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, Parma, Italy.
Front Plant Sci. 2018 Jul 19;9:1063. doi: 10.3389/fpls.2018.01063. eCollection 2018.
It has been known for centuries that floral and extra-floral nectar secreted by plants attracts and rewards animals. Extra-floral nectar is involved in so-called indirect defense by attracting animals (generally ants) that prey on herbivores, or by discouraging herbivores from feeding on the plant. Floral nectar is presented inside the flower close to the reproductive organs and rewards animals that perform pollination while visiting the flower. In both cases nectar is a source of carbon and nitrogen compounds that feed animals, the most abundant solutes being sugars and amino acids. Plant-animal relationships involving the two types of nectar have therefore been used for a long time as text-book examples of symmetric mutualism: services provided by animals to plants in exchange for food provided by plants to animals. Cheating (or deception or exploitation), namely obtaining the reward/service without returning any counterpart, is however, well-known in mutualistic relationships, since the interacting partners have conflicting interests and selection may favor cheating strategies. A more subtle way of exploiting mutualism was recently highlighted. It implies the evolution of strategies to maximize the benefits obtained by one partner while still providing the reward/service to the other partner. Several substances other than sugars and amino acids have been found in nectar and some affect the foraging behavior of insects and potentially increase the benefits to the plant. Such substances can be considered plant cues to exploit mutualism. Recent evidence motivated some authors to use the term "manipulation" of animals by plants in nectar-mediated mutualistic relationships. This review highlights the recent background of the "manipulation" hypothesis, discussing it in the framework of new ecological and evolutionary scenarios in plant-animal interactions, as a stimulus for future research.
几个世纪以来，人们都知道植物分泌的花蜜和花外蜜会吸引并回报动物。花外蜜通过吸引捕食食草动物的动物（通常是蚂蚁），或阻止食草动物取食植物，参与所谓的间接防御。花蜜呈现在花朵内部靠近生殖器官的位置，回报那些在访花时进行授粉的动物。在这两种情况下，花蜜都是为动物提供食物的碳和氮化合物的来源，其中最丰富的溶质是糖和氨基酸。因此，涉及这两种花蜜的植物与动物的关系长期以来一直被用作对称互利共生的教科书式例子：动物为植物提供服务，以换取植物为动物提供的食物。然而，在互利共生关系中，欺骗（或欺诈或剥削），即不回报任何对等物而获取回报/服务，是广为人知的，因为相互作用的伙伴有着相互冲突的利益，选择可能有利于欺骗策略。最近人们强调了一种更微妙的利用互利共生的方式。这意味着进化出一些策略，在仍然向另一个伙伴提供回报/服务的同时，最大化一个伙伴获得的利益。花蜜中除了糖和氨基酸之外还发现了几种其他物质，其中一些会影响昆虫的觅食行为，并可能增加对植物的益处。这些物质可被视为植物利用互利共生的线索。最近的证据促使一些作者在花蜜介导的互利共生关系中使用植物对动物“操纵”这一术语。这篇综述突出了“操纵”假说的最新背景，在植物 - 动物相互作用的新生态和进化场景框架内进行讨论，作为未来研究的一个刺激因素。
