Guangdong Provincial Key Laboratory of Digital Botanical Garden and Key Laboratory of Plant Resource Conservation and Sustainable Utilization, South China Botanical Garden, The Chinese Academy of Sciences, Guangzhou, China.
CEFE, CNRS, Univ Montpellier, EPHE, Montpellier, IRD, France.
BMC Ecol Evol. 2022 Aug 13;22(1):97. doi: 10.1186/s12862-022-02055-0.
In brood site pollination mutualisms, pollinators are attracted by odours emitted at anthesis. In Ficus, odours of receptive figs differ among species and the specific pollinators generally only enter figs of their host species ensuring a pre-zygotic barrier to plant interspecific hybridisation. However, field observations recorded that, in Guangdong province in China, Valisia javana hilli, the local pollinator of F. hirta, entered and reproduced successfully in the figs of the closely related F. triloba on a regular basis. We propose that closely related Ficus species produce similar receptive fig odours. Under particular contexts of odours locally present, the receptive fig odours of non-host figs of a Ficus species may become attractive to pollinators of closely related Ficus species. We used the headspace technique to collect in situ receptive fig odours of F. triloba in a series of locations in China. Under controlled conditions, we tested the attraction of fig pollinating wasps from F. hirta and F. triloba to host figs and non-host figs in Y tube experiments.
Receptive fig odours of F. triloba though different from those of F. hirta, were mainly composed of a same set of volatile organic compounds. When given the choice between receptive fig odours and air, the pollinating wasps were only attracted by their host's odours. However, when given a choice between host and non-host figs the pollinators of F. hirta were equally attracted by the two odours while the pollinators of F. triloba tended to be more attracted by their host's fig odours.
Receptive fig odours vary geographically within species and the differentiation of receptive fig odours between closely related Ficus species is often incomplete. This allows localised or occasional pollinator sharing following different modalities. Cross stimulation when wasps are exposed simultaneously to odours of host and non-host species may be important. While occasional pollinator sharing may play a marginal role when wasp populations are robust, it may ensure the provisioning of new pollinators from the closest relative of a Ficus species if its pollinators go extinct.
在营巢传粉互惠关系中，传粉者会被花期散发的气味吸引。榕属植物的接受榕果的气味在种间存在差异，特定的传粉者通常只进入其宿主种的榕果，从而确保了植物种间杂交的合子前障碍。然而，野外观察记录到，在中国广东省，爪哇榕小蜂（Valisia javana hilli）是 F. hirta 的本地传粉者，它定期进入并成功繁殖与其密切相关的 F. triloba 的榕果。我们提出，密切相关的榕属植物会产生相似的接受榕果气味。在特定的局部气味环境下，非宿主榕果的接受榕果气味可能会对密切相关榕属植物的传粉者具有吸引力。我们使用顶空技术在一系列中国地点收集了 F. triloba 的原位接受榕果气味。在控制条件下，我们在 Y 管实验中测试了来自 F. hirta 和 F. triloba 的榕果传粉蜂对宿主榕果和非宿主榕果的吸引力。
尽管 F. triloba 的接受榕果气味与 F. hirta 的气味不同，但它们主要由同一组挥发性有机化合物组成。当在接受榕果气味和空气之间进行选择时，传粉蜂只被它们宿主的气味所吸引。然而，当在宿主榕果和非宿主榕果之间进行选择时，F. hirta 的传粉者对两种气味的吸引力相等，而 F. triloba 的传粉者则更倾向于被它们宿主的榕果气味所吸引。
接受榕果气味在种内存在地理差异，并且密切相关榕属植物之间的接受榕果气味分化往往不完整。这允许在不同的模式下进行局部或偶尔的传粉者共享。当蜂类同时暴露于宿主和非宿主物种的气味中时，交叉刺激可能很重要。虽然当蜂类种群强大时，偶尔的传粉者共享可能只起次要作用，但如果一个榕属植物的传粉者灭绝，它可以确保从该榕属植物的最亲近的亲缘种中提供新的传粉者。
