使用线粒体基因组信息探讨现生两栖动物的起源和系统进化

熊荣川 邓欢欢 译

摘要：建立现生两栖动物（滑体两栖动物）和它们古代的近缘物种的关系对我们认识早期四足动物的进化非常必要。然而，它们之间的系统发育关系仍然没有得到解决，因为现生两栖动物形态高度特化而且化石相当稀少。古生物学家还不确定滑体两栖动物是单系还是复系，也不确定哪一类古代两栖动物是它们最近的祖先。为了解决这个问题，8个现生两栖动物的线粒体基因组测序完成并将它们和之前发表的序列进行比对。对核苷酸序列作全面的分子系统分析得到一棵高解析度的系统进化树，且和传统的蛙蟾类假设保持一致。通过单独使用分子钟推断分子进化支序的时间信息，我们给出了滑体两栖动物进化的第一个时间尺度，推断其在大约3300万前出现。通过拟合分子钟时间和化石时间，我们认为滑体动物起源于古代temnospondyl两栖动物的假设比其它假设更为可信。而且，在这一时间尺度下，讨论了现生两栖动物的可能起源中心：(i) 现生蛙类（新蛙类群）可能起源于非洲-印度大陆；(ii) 有尾目可能起源于东亚；(iii) 古代无足目可能起源于三叠纪泛大陆的热带森林地区。一个精确的系统发育树及其相关分化时间对指导搜寻缺失的化石有所帮助，而且也能促进两栖动物进化的比较研究。

关键词：两栖动物 线粒体基因组 分子时间推定 系统进化 时间尺度

原文：

Mitogenomic Perspectives on the Origin and Phylogeny of Living Amphibians

Abstract.—Establishing the relationships among modern amphibians (lissamphibians) and their ancient relatives is necessary for our understanding of early tetrapod evolution. However, the phylogeny is still intractable because of the highly specialized anatomy and poor fossil record of lissamphibians. Paleobiologists are still not sure whether lissamphibians are monophyletic or polyphyletic, and which ancient group (temnospondyls or lepospondyls) is most closely related to them. In an attempt to address these problems, eight mitochondrial genomes of living amphibians were determined and compared with previously published amphibian sequences. A comprehensive molecular phylogenetic analysis of nucleotide sequences yields a highly resolved tree congruent with the traditional hypotheses (Batrachia). By using a molecular clock–independent approach for inferring dating information from molecular phylogenies, we present here the first molecular timescale for lissamphibian evolution, which suggests that lissamphibians first emerged about 330 million years ago. By observing the fit between molecular and fossil times, we suggest that the temnospondyl-origin hypothesis for lissamphibians is more credible than other hypotheses. Moreover, under this timescale, the potential geographic origins of the main living amphibian groups are discussed: (i) advanced frogs (neobatrachians) may possess an Africa-India origin; (ii) salamanders may have originated in east Asia; (iii) the tropic forest of the Triassic Pangaea may be the place of origin for the ancient caecilians. An accurate phylogeny with divergence times can be also helpful to direct the search for “missing” fossils, and can benefit comparative studies of amphibian evolution. (Zhang et al., 2005)

[Amphibian; mitochondrial genome; molecular dating; phylogeny; timescale.]

参考文献：

Zhang Peng, Zhou Hui, Chen Yue-Qin, Liu Yi-Fei,Qu Liang-Hu (2005). "Mitogenomic Perspectives on the Origin and Phylogeny of Living Amphibians." Systematic Biology 54(3): 391-400.