Data from: Origins of the endemic scaly tree ferns on the Galápagos and Cocos Islands

Premise of research. Successful long-distance dispersal is rarely observed in scaly tree ferns (Cyatheaceae). Nevertheless, recent molecular evidence has suggested that the four endemic scaly tree ferns on the Galápagos Archipelago (Cyathea weatherbyana) and Cocos Island (Cyathea alfonsiana, Cyathea nesiotica, and Cyathea notabilis), two oceanic island groups west of Central and northern South America, probably each originated from different mainland America ancestors. However, the phylogenetic relationships inferred among these endemics and their mainland relatives have been unclear. This study is aimed at better resolving the relationships and tracing the origins of these island endemics.Methodology. Five plastid regions from 35 Cyathea species were analyzed to reconstruct phylogenetic relationships using parsimony, likelihood, and Bayesian approaches. We also estimated divergence times of these species, and our chronogram was used to reconstruct their biogeographical range history.Pivotal results. Our well-resolved phylogenetic tree of Cyathea, which is in agreement with previous studies, shows that when the four Galápagos and Cocos endemics are included, they each belong to separate subclades. Our biogeographical study suggests that the four endemics originated from independent colonization events from mainland America and that there was no dispersal of Cyathea between the island groups. We reveal more detailed relationships among the endemics and their respective close mainland relatives; some of these relationships differ from previous studies. Our findings are corroborated by new morphological data from ongoing stem anatomy studies.Conclusions. The four scaly tree ferns endemic to the Galápagos and Cocos Islands each did indeed originate as independent colonization events from separate sources in mainland America, and their closest relatives are identified here.

研究前提
鳞桫椤（scaly tree ferns，桫椤科Cyatheaceae）的成功长距离扩散事件鲜有观测记录。尽管如此，近期的分子生物学证据显示，分布于中美洲与南美洲北部以西的两个大洋岛群——加拉帕戈斯群岛（Galápagos Archipelago）与科科斯岛（Cocos Island）的4种特有鳞桫椤，即加拉帕戈斯的桫椤属（Cyathea）Cyathea weatherbyana，以及科科斯岛的Cyathea alfonsiana、Cyathea nesiotica和Cyathea notabilis，大概率各自起源于不同的美洲大陆祖先类群。然而，此前针对这些特有物种与其大陆近缘类群之间的系统发育关系，尚未得到明确解析。本研究旨在更好地厘清这些岛屿特有物种的系统发育关系，并追溯其起源。
研究方法
本研究选取35种桫椤属（Cyathea）植物的5个质体区域（plastid regions），采用简约法（parsimony）、最大似然法（likelihood）与贝叶斯推断法（Bayesian approaches）重构其系统发育关系。本研究同时估算了这些物种的分化时间，并利用构建的时间树（chronogram）重建了它们的生物地理分布历史。
关键结果
本研究获得的桫椤属高分辨率系统发育树与此前研究结果一致，结果显示：当纳入这4种加拉帕戈斯与科科斯岛特有物种时，它们各自隶属于不同的亚支。生物地理分析结果表明，这4种特有物种均起源于来自美洲大陆的独立定殖事件，且这两个岛群之间未发生过桫椤属植物的扩散。本研究还揭示了这些特有物种与其近缘大陆类群之间更为精细的系统发育关系，其中部分关系与此前的研究结论存在差异。本研究的结论得到了正在进行的茎解剖学研究所获得的新形态学数据的支持。
结论
本研究证实，加拉帕戈斯群岛与科科斯岛的4种特有鳞桫椤均起源于来自美洲大陆不同区域的独立定殖事件，本研究同时明确了它们各自的近缘大陆类群。