Yu Hui, Liao Yaolin, Cheng Yufen, Jia Yongxia, Compton Stephen G
Plant Resources Conservation and Sustainable Utilization, South China Botanical Garden, The Chinese Academy of Sciences, Guangzhou, 510650, China.
Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou, 511458, China.
Bot Stud. 2021 Oct 9;62(1):15. doi: 10.1186/s40529-021-00323-8.
The obligate mutualism between fig trees (Ficus, Moraceae) and pollinating fig wasps (Agaonidae) is a model system for studying co-evolution due to its perceived extreme specificity, but recent studies have reported a number of examples of trees pollinated by more than one fig wasp or sharing pollinators with other trees. This will make the potential of pollen flow between species and hybridization more likely though only few fig hybrids in nature have been found. We reared pollinator fig wasps from figs of 13 Chinese fig tree species and established their identity using genetic methods in order to investigate the extent to which they were supporting more than one species of pollinator (co-pollinator).
Our results showed (1) pollinator sharing was frequent among closely-related dioecious species (where pollinator offspring and seeds develop on different trees); (2) that where two pollinator species were developing in figs of one host species there was usually one fig wasp with prominent rate than the other. An exception was F. triloba, where its two pollinators were equally abundant; (3) the extent of co-pollinator within one fig species is related to the dispersal ability of them which is stronger in dioecious figs, especially in small species.
Our results gave more examples to the breakdown of extreme specificity, which suggest that host expansion events where pollinators reproduce in figs other than those of their usual hosts are not uncommon among fig wasps associated with dioecious hosts. Because closely related trees typically have closely related pollinators that have a very similar appearance, the extent of pollinator-sharing has probably been underestimated. Any pollinators that enter female figs carrying heterospecific pollen could potentially generate hybrid seed, and the extent of hybridization and its significance may also have been underestimated.
榕树（桑科榕属）与传粉榕小蜂（榕小蜂科）之间的专性互利共生关系，因其高度的特异性，是研究协同进化的一个模式系统。但最近的研究报告了许多由不止一种榕小蜂传粉的树木，或与其他树木共享传粉者的例子。这使得物种间花粉流动和杂交的可能性增加，尽管在自然界中仅发现了少数榕属杂交种。我们从13种中国榕树的果实中饲养传粉榕小蜂，并使用遗传方法确定它们的身份，以调查它们支持不止一种传粉者（共同传粉者）的程度。
我们的结果表明：（1）在亲缘关系密切的雌雄异株物种（传粉者后代和种子在不同的树上发育）中，传粉者共享很常见；（2）在一个寄主物种的果实中发育的两种传粉者物种中，通常有一种榕小蜂的数量比另一种多。三叶榕是个例外，其两种传粉者数量相当；（3）一个榕属物种内共同传粉者的程度与其扩散能力有关，在雌雄异株的榕属植物中扩散能力更强，尤其是在小型物种中。
我们 的结果为极端特异性的打破提供了更多例子，这表明在与雌雄异株寄主相关的榕小蜂中，传粉者在其通常寄主以外的果实中繁殖的寄主扩展事件并不罕见。由于亲缘关系密切的树木通常有外观非常相似的亲缘关系密切的传粉者，传粉者共享的程度可能被低估了。任何携带异种花粉进入雌果的传粉者都有可能产生杂交种子，杂交的程度及其重要性也可能被低估了。
