Department of Biological Sciences, Sungkyunkwan University, Suwon, Korea.
Department of Botany, Graduate School of Science, Kyoto University, Kyoto, Japan.
Am J Bot. 2024 Sep;111(9):e16403. doi: 10.1002/ajb2.16403. Epub 2024 Sep 11.
Island plants have long interested biologists because of their distinctive morphological features and their isolation on small land areas in vast oceans. Studies of insular endemics may include identifying their ancestors, tracing their dispersal to islands, and describing their evolution on islands, including characters adaptive to island life. Thamnoseris is a monospecific genus endemic to the Desventuradas Islands, Chile. Its origins and relationships are unresolved, given the challenges of getting to the islands and accessing plants there.
Sequences from ITS of nrDNA and the complete chloroplast genome were employed to resolve phylogenetic relationships of Thamnoseris.
Phylogenetic analyses of nuclear and chloroplast sequences showed Thamnoseris nested within or sister to Dendroseris, the largest endemic genus in the Juan Fernández Islands.
Thamnoseris evolved from a common ancestor of all or most species of Dendroseris prior to the diversification of Dendroseris in the Juan Fernández archipelago. The ancestor of Thamnoseris dispersed to the Desventuradas archipelago, which consists of the islands San Ambrosio and San Félix, within the past 3 Ma (the age of San Ambrosio). This is the only known example of possible plant dispersa\l between the Juan Fernández and Desventuradas Islands. We also mention two less likely biogeographic scenarios for the origin of Thamnoseris, which has features not seen in Dendroseris: small capitula with yellow florets; style branches barely divergent; and basally swollen subtending involucral bracts, all features associated with selfing and reduced dispersal. Goats and rabbits (now removed) reduced T. lacerata, once very abundant on the Desventuradas Islands, to several plants, making it of extreme conservation concern and worthy of further study.
由于岛屿植物具有独特的形态特征和在广阔海洋中的小面积土地上的隔离，它们一直引起生物学家的兴趣。对岛屿特有种的研究可能包括确定它们的祖先，追踪它们向岛屿的扩散，以及描述它们在岛屿上的进化，包括适应岛屿生活的特征。Thamnoseris 是智利德斯文图拉达斯群岛特有的单种属。由于到达这些岛屿并获取那里的植物存在挑战，因此其起源和关系仍未得到解决。
使用 ITS 的 nrDNA 和完整的叶绿体基因组序列来解决 Thamnoseris 的系统发育关系。
核和叶绿体序列的系统发育分析表明，Thamnoseris 嵌套在 Juan Fernández 群岛中最大的特有属 Dendroseris 内或与其为姐妹关系。
Thamnoseris 是在 Dendroseris 在 Juan Fernández 群岛多样化之前，从所有或大多数 Dendroseris 物种的共同祖先进化而来的。Thamnoseris 的祖先在过去 300 万年（圣安布罗西奥岛的年龄）内分散到德斯文图拉达斯群岛，该群岛由圣安布罗西奥岛和圣费利克斯岛组成。这是 Juan Fernández 和德斯文图拉达斯群岛之间可能的植物传播的唯一已知例子。我们还提到了 Thamnoseris 起源的两种不太可能的生物地理情景，它具有在 Dendroseris 中未见的特征：小花黄色头状花序；花柱分枝几乎不发散；基部肿胀的托叶状苞片，所有这些特征都与自交和减少传播有关。山羊和兔子（现已移除）使曾经在德斯文图拉达斯群岛非常丰富的 T. lacerata 减少到几株植物，这使其成为极端保护关注的对象，值得进一步研究。
