Zardoya R, Meyer A
Museo Nacional de Ciencias Naturales, Madrid, Spain.
Genetics. 2000 Jun;155(2):765-75. doi: 10.1093/genetics/155.2.765.
The complete nucleotide sequence (17,005 bp) of the mitochondrial genome of the caecilian Typhlonectes natans (Gymnophiona, Amphibia) was determined. This molecule is characterized by two distinctive genomic features: there are seven large 109-bp tandem repeats in the control region, and the sequence for the putative origin of replication of the L strand can potentially fold into two alternative secondary structures (one including part of the tRNA(Cys)). The new sequence data were used to assess the phylogenetic position of caecilians and to gain insights into the origin of living amphibians (frogs, salamanders, and caecilians). Phylogenetic analyses of two data sets-one combining protein-coding genes and the other combining tRNA genes-strongly supported a caecilian + frog clade and, hence, monophyly of modern amphibians. These two data sets could not further resolve relationships among the coelacanth, lungfishes, and tetrapods, but strongly supported diapsid affinities of turtles. Phylogenetic relationships among a larger set of species of frogs, salamanders, and caecilians were estimated with a mitochondrial rRNA data set. Maximum parsimony analysis of this latter data set also recovered monophyly of living amphibians and favored a frog + salamander (Batrachia) relationship. However, bootstrap support was only moderate at these nodes. This is likely due to an extensive among-site rate heterogeneity in the rRNA data set and the narrow window of time in which the three main groups of living amphibians were originated.
已确定了盲螈（Typhlonectes natans，蚓螈目，两栖纲）线粒体基因组的完整核苷酸序列（17,005 bp）。该分子具有两个独特的基因组特征：控制区有七个109 bp的大串联重复序列，L链推定复制起点的序列可能折叠成两种替代二级结构（一种包括tRNA(Cys)的一部分）。新的序列数据用于评估蚓螈的系统发育位置，并深入了解现存两栖动物（青蛙、蝾螈和蚓螈）的起源。对两个数据集进行的系统发育分析——一个结合蛋白质编码基因，另一个结合tRNA基因——有力地支持了蚓螈 + 青蛙分支，因此支持现代两栖动物的单系性。这两个数据集无法进一步解析腔棘鱼、肺鱼和四足动物之间的关系，但有力地支持了龟类的双孔类亲缘关系。利用线粒体rRNA数据集估计了更大量的青蛙、蝾螈和蚓螈物种之间的系统发育关系。对后一个数据集进行的最大简约分析也恢复了现存两栖动物的单系性，并支持青蛙 + 蝾螈（无尾目）的关系。然而，这些节点处的自展支持率仅为中等。这可能是由于rRNA数据集中位点间广泛的速率异质性以及现存两栖动物三个主要类群起源的时间窗口较窄所致。
