Molecular Phylogeny and Evolution of Compositae of the Juan Fernandez Islands

俄亥俄州立大学的丹·克劳福德博士和托德·斯图西博士将利用分子DNA信息研究胡安费尔南德斯群岛上三个植物属的进化，该群岛位于智利中部以西600公里处。大洋岛，特别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进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。在胡安费尔南德斯，较老的岛(Masatiera)有400万年的历史，而较年轻的Masafuera岛的历史有一到两百万年。胡安·费尔南德斯的植物区系数量很少，但含有很高比例的独特(特有)物种。这使得研究该群岛特有植物的起源和演化成为可能。两个最大的特有属是菊科向日葵属Dendroseris和Robinsonia。这些是奇怪的树状植物，只能通过形态比较来猜测它们来自南美大陆的推测祖先。利用分子特征如叶绿体DNA限制酶位点和序列、核糖体DNA和蛋白质同工酶将有助于将岛屿类群与大陆物种进行比较，并确定可能的祖先种群。分子方法也将被用来确定岛屿上Dendroseris和Robinsonia物种之间的进化关系，并研究群岛上第三个属的进化。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状植物的起源和系统发育关系，就有可能研究与扩散到孤立的海洋岛屿和在其上建立有关的生命形式和生理上的重要变化。这反过来应有助于更好地理解新植物物种进化所涉及的过程。

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.