Staab Michael, Fornoff Felix, Klein Alexandra-Maria, Blüthgen Nico
Am Nat. 2017 Sep;190(3):442-450. doi: 10.1086/692735. Epub 2017 Jun 23.
Extrafloral nectaries (EFNs) allow plants to engage in mutualisms with ants, preventing herbivory in exchange for food. EFNs occur scattered throughout the plant phylogeny and likely evolved independent from herbivore-created wounds subsequently visited by ants collecting leaked sap. Records of wound-feeding ants are, however, anecdotal. By surveying 38,000 trees from 40 species, we conducted the first quantitative ecological study of this overlooked behavior. Ant-wound interactions were widespread (0.5% of tree individuals) and occurred on 23 tree species. Interaction networks were opportunistic, closely resembling ant-EFN networks. Fagaceae, a family lacking EFNs, was strongly overrepresented. For Fagaceae, ant occurrence at wounds correlated with species-level leaf damage, potentially indicating that wounds may attract mutualistic ants, which supports the hypothesis of ant-tended wounds as precursors of ant-EFN mutualisms. Given that herbivore wounds are common, wound sap as a steadily available food source might further help to explain the overwhelming abundance of ants in (sub)tropical forest canopies.
花外蜜腺（EFNs）使植物能够与蚂蚁建立互利共生关系，以食物为交换防止食草动物侵害。花外蜜腺分散存在于整个植物系统发育过程中，可能独立于食草动物造成的伤口进化而来，随后蚂蚁会采集从这些伤口渗出的汁液。然而，关于以伤口为食的蚂蚁的记录只是传闻。通过对40个物种的38000棵树进行调查，我们首次对这种被忽视的行为进行了定量生态学研究。蚂蚁与伤口的相互作用很普遍（占树木个体的0.5%），且发生在23种树上。相互作用网络具有机会主义性，与蚂蚁-花外蜜腺网络非常相似。缺乏花外蜜腺的壳斗科在其中的占比严重过高。对于壳斗科而言，伤口处蚂蚁的出现与物种水平的叶片损伤相关，这可能表明伤口可能会吸引互利共生的蚂蚁，这支持了蚂蚁照料的伤口是蚂蚁-花外蜜腺互利共生关系前身的假说。鉴于食草动物造成的伤口很常见，伤口汁液作为一种稳定的食物来源可能进一步有助于解释（亚）热带森林树冠层中蚂蚁数量众多的现象。
