Phylogeographical studies on the origin and evolution of plants in the Bonin Islands, Japan

在本研究中，我们对几个分类群进行了分子系统地理学分析，以阐明发生在日本小笠原群岛的物种的地理起源。我们从琉球、台湾、菲律宾、关岛、夏威夷群岛等博宁群岛及其周边地区收集了几种植物材料。系统发育结果表明，博宁群岛特有的Gynochthodes boninensis （Rubiaceae）与台湾的G. parvifolia亲缘关系最密切，而不是与博宁岛特有的G. umbellata亲缘关系。这一结果表明，博宁鸡可能起源于一个原产于东亚的祖先。据报道，boninensis具有雄雄异株性系统，这在开花植物中是罕见的，而其近亲parvipolia G.和伞形G.是雌雄异株的。本种的雄雄异株性系统可能是从雌雄异株进化而来的。

In the present study, we conducted a molecular phylogeographic analysis of several taxa to elucidate the geographical origin of the species occurring in the Bonin Islands, Japan. We collected several plant materials from the Bonin Islands and its surrounding areas, such as the Ryukyus, Taiwan, the Philippines, Guam, and the Hawaiian Islands. Our phylogenetic results showed that Gynochthodes boninensis (Rubiaceae), endemic to the Bonin Islands is most closely related to G. parvifolia from Taiwan rather than G. umbellata, which was treated as the same species as G. boninensis. This result suggests that G. boninensis may have originated from a progenitor native to eastern Asia. Gynochthodes boninensis is reported to have an androdioecious sexual system, which is rare in flowering plants, whereas its closely relatives, G. parvipolia and G. umbellata are dioecious. The androdioecious sexual system of this species may have evolved from dioecy.