Böhle U R, Hilger H H, Martin W F
Institut für Systematische Botanik und Pflanzengeographie, Freie Universität Berlin, Germany.
Proc Natl Acad Sci U S A. 1996 Oct 15;93(21):11740-5. doi: 10.1073/pnas.93.21.11740.
Numerous island-inhabiting species of predominantly herbaceous angiosperm genera are woody shrubs or trees. Such "insular woodiness" is strongly manifested in the genus Echium, in which the continental species of circummediterranean distribution are herbaceous, whereas endemic species of islands along the Atlantic coast of north Africa are woody perennial shrubs. The history of 37 Echium species was traced with 70 kb of noncoding DNA determined from both chloroplast and nuclear genomes. In all, 239 polymorphic positions with 137 informative sites, in addition to 27 informative indels, were found. Island-dwelling Echium species are shown to descend from herbaceous continental ancestors via a single island colonization event that occurred < 20 million years ago. Founding colonization appears to have taken place on the Canary Islands, from which the Madeira and Cape Verde archipelagos were invaded. Colonization of island habitats correlates with a recent origin of perennial woodiness from herbaceous habit and was furthermore accompanied by intense speciation, which brought forth remarkable diversity of forms among contemporary island endemics. We argue that the origin of insular woodiness involved response to counter-selection of inbreeding depression in founding island colonies.
许多主要为草本被子植物属的岛屿栖息物种是木本灌木或乔木。这种“岛屿木本化”在蓝蓟属中表现得很强烈，在地中海周边分布的大陆物种是草本植物，而北非大西洋沿岸岛屿的特有物种是多年生木本灌木。利用从叶绿体和核基因组中确定的70 kb非编码DNA追踪了37种蓝蓟属植物的历史。总共发现了239个多态性位点，其中137个信息位点，此外还有27个信息插入缺失。研究表明，岛屿栖息的蓝蓟属物种是在不到2000万年前通过一次单一的岛屿殖民事件从草本大陆祖先演化而来的。最初的殖民似乎发生在加那利群岛，马德拉群岛和佛得角群岛随后从那里被入侵。岛屿栖息地的殖民与从草本习性到多年生木本习性的近期起源相关，并且还伴随着强烈的物种形成，这在当代岛屿特有物种中产生了显著的形态多样性。我们认为，岛屿木本化的起源涉及对建立岛屿殖民地时近亲繁殖衰退的反向选择的响应。
