Emerson Brent C, Faria Christiana M A
Island Ecology and Evolution Research Group, Instituto de Productos Naturales y Agrobiología (IPNA-CSIC), C/Astrofísico Francisco Sánchez 3, San Cristóbal de La Laguna, Santa Cruz de Tenerife, 38206, Spain.
Mol Ecol. 2014 Nov;23(21):5132-4. doi: 10.1111/mec.12951.
A well-used metaphor for oceanic islands is that they act as 'natural laboratories' for the study of evolution. But how can islands or archipelagos be considered analogues of laboratories for understanding the evolutionary process itself? It is not necessarily the case that just because two or more related species occur on an island or archipelago, somehow, this can help us understand more about their evolutionary history. But in some cases, it can. In this issue of Molecular Ecology, Garrick et al. () use population-level sampling within closely related taxa of Galapagos giant tortoises to reveal a complex demographic history of the species Chelonoidis becki - a species endemic to Isabela Island, and geographically restricted to Wolf Volcano. Using microsatellite genotyping and mitochondrial DNA sequencing, they provide a strong case for C. becki being derived from C. darwini from the neighbouring island of Santiago. But the interest here is that colonization did not happen only once. Garrick et al. () reveal C. becki to be the product of a double colonization event, and their data reveal these two founding lineages to be now fusing back into one. Their results are compelling and add to a limited literature describing the evolutionary consequences of double colonization events. Here, we look at the broader implications of the findings of Garrick et al. () and suggest genomic admixture among multiple founding populations may be a characteristic feature within insular taxa.
对于海洋岛屿，一个常用的比喻是它们充当了研究进化的“天然实验室”。但是，岛屿或群岛如何能被视为理解进化过程本身的实验室类似物呢？仅仅因为在一个岛屿或群岛上出现了两个或更多相关物种，这并不一定能帮助我们更多地了解它们的进化历史。但在某些情况下，确实可以。在本期《分子生态学》中，加里克等人利用加拉帕戈斯巨型陆龟密切相关分类群内的种群水平抽样，揭示了贝克氏陆龟（Chelonoidis becki）这一物种复杂的种群历史——该物种是伊莎贝拉岛特有的，地理分布局限于沃尔夫火山。通过微卫星基因分型和线粒体DNA测序，他们有力地证明了贝克氏陆龟源自邻近圣地亚哥岛的达尔文氏陆龟（C. darwini）。但这里有趣的是，殖民化并非只发生过一次。加里克等人揭示贝克氏陆龟是双重殖民化事件的产物，他们的数据显示这两个奠基谱系现在正重新融合为一个。他们的结果令人信服，并为描述双重殖民化事件进化后果的有限文献增添了内容。在此，我们探讨加里克等人研究结果的更广泛意义，并提出多个奠基种群之间的基因组混合可能是岛屿分类群的一个特征。
