Molecular Phylogeny and Evolution of Compositae of the Juan Fernandez Islands

Drs。俄亥俄州立大学的Dan Crawford和Tod Stuessy将利用分子DNA信息来研究Juan Fernandez群岛上三种植物的进化，该群岛位于智利中部以西600公里处。大洋岛屿，尤其是胡安·费尔南德斯群岛，为研究植物进化提供了理想的系统。对海洋岛屿上植物的起源和演化设定一个时间框架是可能的，因为这些岛屿的地质年代可以相当准确地确定。在Juan Fernandez，较老的岛屿（Masatierra）有400万年的历史，而较年轻的马萨弗拉岛（Masafuera）只有100万年到200万年的历史。胡安费尔南德斯的植物群数量很少，但含有很高比例的独特（特有）物种。这使得研究群岛特有植物的起源和进化成为可能。两个最大的地方性属是菊科向日葵科的石斛属和罗宾逊属。这是一种奇怪的树状植物，据推测其祖先来自南美大陆，只能通过形态学比较来猜测。利用叶绿体DNA限制性内切位点和序列、核糖体DNA和蛋白质同型酶等分子特征将有助于将岛屿分类群与大陆物种进行比较，并确定可能的祖先种群。还将采用分子方法来确定岛上的石斛属和罗宾逊属物种之间的进化关系，并研究群岛上第三个属——Erigeron的进化。与智利科学家和学生的实地考察将为这些综合研究提供材料。一旦用DNA和蛋白质数据确定了这些岛屿植物的起源和系统发育关系，就有可能研究与分散到孤立的海洋岛屿并在岛上定居有关的生命形式和生理学的重要变化。这反过来又会导致对新植物物种进化过程的更好理解。

Drs. Dan Crawford and Tod Stuessy of Ohio State University will use molecular DNA information to study the evolution of three genera of plants occurring on the Juan Fernandez Islands, located 600 km west of central Chile. Oceanic islands, and the Juan Fernandez archipelago in particular, offer ideal systems in which to study plant evolution. It is possible to place a time frame on the origin and evolution of plants on oceanic islands because the islands can be dated geologically with reasonable accuracy. In the Juan Fernandez, the older island (Masatierra) is four million years old while the age of the younger island of Masafuera is one to two million years. The flora of the Juan Fernandez is small in numbers but contains a high percentage of unique (endemic) species. This makes it feasible to study the origin and evolution of the endemic plants on the archipelago. The two largest endemic genera are Dendroseris and Robinsonia in the sunflower family, Asteraceae. These are bizarre tree-like plants whose presumptive ancestors from the South American mainland can only be guessed from morphological comparisons. The use of molecular characters such as chloroplast DNA restriction sites and sequences, ribosomal DNA, and protein iszoymes will help to compare the island taxa with mainland species and determine possible progenitor stocks. Molecular methods will also be employed to determine evolutionary relationships among the species of Dendroseris and Robinsonia on the islands, and to study the evolution of a third genus in the archipelago, Erigeron. Field trips with Chilean scientists and students will provide materials for these comprehensive studies. Once origins and phylogenetic relationships of these insular plants are determined with DNA and protein data, it will be possible to study the important changes in life-form and physiology associated with dispersal to and establishment upon isolated oceanic islands. This in turn should lead to a better understanding of processes involved in the evolution of new plant species.