Department of Ecology and Evolutionary Biology and Yale Institute for Biospheric Studies - Molecular Systematics and Conservation Genetics Laboratory, New Haven, Connecticut 06511, USA.
BMC Evol Biol. 2009 Dec 22;9:297. doi: 10.1186/1471-2148-9-297.
Marine iguanas (Amblyrhynchus cristatus) inhabit the coastlines of large and small islands throughout the Galápagos archipelago, providing a rich system to study the spatial and temporal factors influencing the phylogeographic distribution and population structure of a species. Here, we analyze the microevolution of marine iguanas using the complete mitochondrial control region (CR) as well as 13 microsatellite loci representing more than 1200 individuals from 13 islands.
CR data show that marine iguanas occupy three general clades: one that is widely distributed across the northern archipelago, and likely spread from east to west by way of the South Equatorial current, a second that is found mostly on the older eastern and central islands, and a third that is limited to the younger northern and western islands. Generally, the CR haplotype distribution pattern supports the colonization of the archipelago from the older, eastern islands to the younger, western islands. However, there are also signatures of recurrent, historical gene flow between islands after population establishment. Bayesian cluster analysis of microsatellite genotypes indicates the existence of twenty distinct genetic clusters generally following a one-cluster-per-island pattern. However, two well-differentiated clusters were found on the easternmost island of San Cristóbal, while nine distinct and highly intermixed clusters were found on youngest, westernmost islands of Isabela and Fernandina. High mtDNA and microsatellite genetic diversity were observed for populations on Isabela and Fernandina that may be the result of a recent population expansion and founder events from multiple sources.
While a past genetic study based on pure FST analysis suggested that marine iguana populations display high levels of nuclear (but not mitochondrial) gene flow due to male-biased dispersal, the results of our sex-biased dispersal tests and the finding of strong genetic differentiation between islands do not support this view. Therefore, our study is a nice example of how recently developed analytical tools such as Bayesian clustering analysis and DNA sequence-based demographic analyses can overcome potential biases introduced by simply relying on FST estimates from markers with different inheritance patterns.
海鬣蜥（Amblyrhynchus cristatus）栖息在加拉帕戈斯群岛大大小小的岛屿海岸线上，为研究影响物种谱系地理分布和种群结构的时空因素提供了丰富的系统。在这里，我们使用完整的线粒体控制区（CR）以及代表来自 13 个岛屿的 1200 多个个体的 13 个微卫星基因座来分析海鬣蜥的微观进化。
CR 数据显示，海鬣蜥占据了三个一般的进化枝：一个广泛分布在北部群岛，可能是通过赤道逆流从东向西传播；另一个主要分布在较古老的东部和中部岛屿；第三个局限于较年轻的北部和西部岛屿。一般来说，CR 单倍型分布模式支持从较老的东部岛屿向较年轻的西部岛屿的殖民化。然而，在种群建立后，也存在着岛屿间反复发生的历史基因流的迹象。微卫星基因型的贝叶斯聚类分析表明，存在二十个不同的遗传簇，通常遵循一个簇一个岛屿的模式。然而，在最东部的圣克里斯托瓦尔岛上发现了两个分化良好的聚类，而在最年轻的西部的伊莎贝拉岛和费尔南迪纳岛上发现了九个独特且高度混合的聚类。在伊莎贝拉岛和费尔南迪纳岛上的种群中观察到了高的 mtDNA 和微卫星遗传多样性，这可能是由于最近的种群扩张和来自多个来源的奠基者事件所致。
虽然过去的一项基于纯 FST 分析的遗传研究表明，由于雄性偏性扩散，海鬣蜥种群显示出高水平的核（但不是线粒体）基因流，但我们的性别偏性扩散测试结果和岛屿间强烈的遗传分化并不支持这一观点。因此，我们的研究是一个很好的例子，说明如何利用最近开发的分析工具，如贝叶斯聚类分析和基于 DNA 序列的种群动态分析，可以克服仅仅依赖具有不同遗传模式的标记的 FST 估计所带来的潜在偏差。
