Yu Teng-Lang, Lin Hung-Du, Weng Ching-Feng
Department of Life Science and Institute of Biotechnology, National Dong Hwa University, Hualien, Taiwan.
The Affiliated School of National Tainan First Senior High School, Tainan, Taiwan.
PLoS One. 2014 May 22;9(5):e98029. doi: 10.1371/journal.pone.0098029. eCollection 2014.
To comprehend the phylogeographic patterns of genetic variation in anurans at Taiwan Island, this study attempted to examine (1) the existence of various geological barriers (Central Mountain Ranges, CMRs); and (2) the genetic variation of Bufo bankorensis using mtDNA sequences among populations located in different regions of Taiwan, characterized by different climates and existing under extreme conditions when compared available sequences of related species B. gargarizans of mainland China.
METHODOLOGY/PRINCIPAL FINDINGS: Phylogenetic analyses of the dataset with mitochondrial DNA (mtDNA) D-loop gene (348 bp) recovered a close relationship between B. bankorensis and B. gargarizans, identified three distinct lineages. Furthermore, the network of mtDNA D-loop gene (564 bp) amplified (279 individuals, 27 localities) from Taiwan Island indicated three divergent clades within B. bankorensis (Clade W, E and S), corresponding to the geography, thereby verifying the importance of the CMRs and Kaoping River drainage as major biogeographic barriers. Mismatch distribution analysis, neutrality tests and Bayesian skyline plots revealed that a significant population expansion occurred for the total population and Clade W, with horizons dated to approximately 0.08 and 0.07 Mya, respectively. These results suggest that the population expansion of Taiwan Island species B. bankorensis might have resulted from the release of available habitat in post-glacial periods, the genetic variation on mtDNA showing habitat selection, subsequent population dispersal, and co-distribution among clades.
The multiple origins (different clades) of B. bankorensis mtDNA sequences were first evident in this study. The divergent genetic clades found within B. bankorensis could be independent colonization by previously diverged lineages; inferring B. bankorensis originated from B. gargarizans of mainland China, then dispersal followed by isolation within Taiwan Island. Highly divergent clades between W and E of B. bankorensis, implies that the CMRs serve as a genetic barrier and separated the whole island into the western and eastern phylogroups.
为了解台湾岛无尾两栖类动物的遗传变异系统发育地理格局，本研究试图检验：（1）各种地质屏障（中央山脉）的存在；（2）利用线粒体DNA序列，研究台湾不同地区、不同气候条件及极端环境下的高山蟾蜍种群的遗传变异，并与中国大陆的中华大蟾蜍相关序列进行比较。
方法/主要发现：对线粒体DNA（mtDNA）D-loop基因（348 bp）数据集进行系统发育分析，发现高山蟾蜍与中华大蟾蜍关系密切，确定了三个不同的谱系。此外，从台湾岛扩增的线粒体DNA D-loop基因（564 bp）网络（279个个体，27个地点）显示，高山蟾蜍内部分为三个不同的分支（W、E和S分支），与地理分布相对应，从而验证了中央山脉和高屏溪排水系统作为主要生物地理屏障的重要性。失配分布分析、中性检验和贝叶斯天际线图显示，总种群和W分支发生了显著的种群扩张，时间分别约为0.08和0.07百万年前。这些结果表明，台湾岛物种高山蟾蜍的种群扩张可能是由于冰期后可用栖息地的释放，mtDNA上的遗传变异显示出栖息地选择、随后的种群扩散以及分支间的共同分布。
本研究首次明确了高山蟾蜍线粒体DNA序列的多个起源（不同分支）。在高山蟾蜍中发现的不同遗传分支可能是先前分化的谱系独立定殖的结果；推断高山蟾蜍起源于中国大陆的中华大蟾蜍，然后在台湾岛内扩散并隔离。高山蟾蜍W分支和E分支之间的高度分化，意味着中央山脉是一个遗传屏障，将整个岛屿分为西部和东部的系统发育类群。
