JT Biohistory Research Hall, Takatsuki, Osaka, 569-1125, Japan.
Department of Biological Sciences, Graduate School of Science, Osaka University, Osaka, 560-0043, Japan.
Commun Biol. 2022 Apr 8;5(1):284. doi: 10.1038/s42003-022-03223-0.
The obligate pollination mutualism between figs (Ficus, Moraceae) and pollinator wasps (Agaonidae, Hymenoptera) is a classic example of cospeciation. However, examples of phylogenetic incongruencies between figs and their pollinators suggest that pollinators may speciate by host shifting. To investigate the mechanism of speciation by host shifting, we examined the phylogenetic relationships and population genetic structures of six closely related fig species and their pollinators from southern China and Taiwan-Ryukyu islands using various molecular markers. The results revealed 1) an extraordinary case of pollinator sharing, in which five distinct fig species share a single pollinator species in southern China; 2) two types of copollination, namely, sympatric copollination by pollinator duplication or pollinator migration, and allopatric copollination by host migration and new pollinator acquisition; 3) fig species from southern China have colonized Taiwan repeatedly and one of these events has been followed by host shifting, reestablishment of host specificity, and pollinator speciation, in order. Based on our results, we propose a model for pollinator speciation by host shifting in which the reestablishment of host-specificity plays a central role in the speciation process. These findings provide important insights into understanding the mechanisms underlying pollinator speciation and host specificity in obligate pollination mutualism.
榕属植物（榕属，桑科）与其传粉榕小蜂（榕小蜂科，膜翅目）之间的专性传粉互惠关系是协同进化的经典范例。然而，榕属植物与其传粉者之间的系统发育不一致的例子表明，传粉者可能通过寄主转移而发生物种形成。为了研究寄主转移导致物种形成的机制，我们利用多种分子标记，研究了来自中国南方和台湾-琉球群岛的六个密切相关的榕属植物及其传粉者的系统发育关系和种群遗传结构。结果揭示了：1）传粉者共享的一个特殊案例，即中国南方的五个不同的榕属植物物种与一个单一的传粉者物种共享；2）两种共传粉方式，即通过传粉者复制或传粉者迁移的同域共传粉，以及通过寄主迁移和新传粉者获得的异域共传粉；3）来自中国南方的榕属植物已多次殖民台湾，其中一个事件伴随着寄主转移、寄主专一性的重新建立以及传粉者的物种形成。基于我们的结果，我们提出了一个寄主转移导致传粉者物种形成的模型，其中寄主专一性的重新建立在物种形成过程中起着核心作用。这些发现为理解专性传粉互惠关系中传粉者物种形成和寄主专一性的机制提供了重要的见解。
