Takayama Koji, Crawford Daniel J, López-Sepúlveda Patricio, Greimler Josef, Stuessy Tod F
Graduate School of Science, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto, 606-8502, Japan.
Department of Ecology and Evolutionary Biology, Biodiversity Institute, University of Kansas, Lawrence, KS, 60045, USA.
J Plant Res. 2018 May;131(3):469-485. doi: 10.1007/s10265-018-1023-z. Epub 2018 Mar 13.
Adaptive radiation is a common evolutionary phenomenon in oceanic islands. From one successful immigrant population, dispersal into different island environments and directional selection can rapidly yield a series of morphologically distinct species, each adapted to its own particular environment. Not all island immigrants, however, follow this evolutionary pathway. Others successfully arrive and establish viable populations, but they remain in the same ecological zone and only slowly diverge over millions of years. This transformational speciation, or anagenesis, is also common in oceanic archipelagos. The critical question is why do some groups radiate adaptively and others not? The Juan Fernández Islands contain 105 endemic taxa of angiosperms, 49% of which have originated by adaptive radiation (cladogenesis) and 51% by anagenesis, hence providing an opportunity to examine characteristics of taxa that have undergone both types of speciation in the same general island environment. Life form, dispersal mode, and total number of species in progenitors (genera) of endemic angiosperms in the archipelago were investigated from literature sources and compared with modes of speciation (cladogenesis vs. anagenesis). It is suggested that immigrants tending to undergo adaptive radiation are herbaceous perennial herbs, with leaky self-incompatible breeding systems, good intra-island dispersal capabilities, and flexible structural and physiological systems. Perhaps more importantly, the progenitors of adaptively radiated groups in islands are those that have already been successful in adaptations to different environments in source areas, and which have also undergone eco-geographic speciation. Evolutionary success via adaptive radiation in oceanic islands, therefore, is less a novel feature of island lineages but rather a continuation of tendency for successful adaptive speciation in lineages of continental source regions.
适应辐射是海洋岛屿中常见的进化现象。从一个成功的迁入种群开始，扩散到不同的岛屿环境并经过定向选择，能够迅速产生一系列形态各异的物种，每个物种都适应其特定的环境。然而，并非所有岛屿迁入者都遵循这种进化路径。其他一些迁入者成功抵达并建立了可存活的种群，但它们仍处于相同的生态区域，仅在数百万年的时间里缓慢分化。这种渐变式物种形成，即前进演化，在海洋群岛中也很常见。关键问题是，为什么有些类群会进行适应性辐射而有些则不会？胡安·费尔南德斯群岛拥有105种被子植物特有分类群，其中49%起源于适应性辐射（分支进化），51%起源于前进演化，因此提供了一个机会来研究在同一岛屿总体环境中经历了两种物种形成类型的分类群的特征。从文献资料中研究了该群岛被子植物特有类群的生活型、扩散模式以及祖先（属）中的物种总数，并与物种形成模式（分支进化与前进演化）进行了比较。研究表明，倾向于进行适应性辐射的迁入者是多年生草本植物，具有自交不亲和的繁殖系统、良好的岛内扩散能力以及灵活的结构和生理系统。也许更重要的是，岛屿中通过适应性辐射形成的类群的祖先，是那些在源区已经成功适应不同环境并且也经历了生态地理物种形成的类群。因此，海洋岛屿中通过适应性辐射实现的进化成功，与其说是岛屿谱系的一个新特征，不如说是大陆源区谱系中成功适应性物种形成趋势的延续。
