28S and 18S rDNA sequences support the monophyly of lampreys and hagfishes
28S and 18S rDNA sequences support the monophyly of lampreys and hagfishes
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DOI：
10.1093/oxfordjournals.molbev.a025897
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发表时间：
1998-12-01
影响因子：
10.7
通讯作者：
Sullivan, J
中科院分区：
文献类型：
--
作者：
Mallat, J;Sullivan, J
解决脊椎动物的三个主要现存谱系（八目鳗，七鳃鳗和有颌动物）的相互关系是进化中一个特别重要的问题，因为基础分辨率严重影响我们对原始脊椎动物特征的理解。在过去的20年里，一个共识已经出现，即七鳃鳗是安氏颚口鳗的姐妹群，八目鳗代表了一个古老的、基础的谱系。这一假说基本上取代了单系的圆口类（七鳃鳗加八目鳗）的经典假说。为了验证这些假设，我们比较了几乎完整的核糖体DNA序列，从每个这些主要的血统，以及那些从头索动物和尾索动物，这代表了一个并系外群评估基础脊椎动物的关系。为了进行比较，92%-99%的完整的28 S rDNA序列，从文昌鱼Branchiostoma floridae，八目鳗Eptatretus starcus，七鳃鳗Petromyzon marinus，和软骨鱼类Hydrolagus colliei和Squalus acanthias，然后与以前报道的28 S和18 S rDNA序列进行了分析，从其他脊索动物。我们进行了传统的（非参数）bootstrap分析，根据最大似然，简约，最小进化（使用LogDet距离）的标准，28 S和18 S rDNA序列分别考虑和组合。所有这些分析为圆口动物的单系性提供了中等到非常强的支持。此外，目前接受的七鳃鳗-颚口类分支的假设被Kishino-Hasegawa检验适度拒绝（P = 0.099），并被参数bootstrap检验彻底拒绝（P < 0.01），支持单系生活圆口类。另一个重要的发现是八目鳗E. Staphylococcus是已知生物中最长的28 S rDNA基因（> 5，200 nt）。
Resolving the interrelationships of three major extant lineages of vertebrates (hagfishes, lampreys, and gnathostomes) is a particularly important issue in evolution because the basal resolution critically influences our understanding of primitive vertebrate characters. A consensus has emerged over the last 20 years that lampreys are the sister group to the gnathostomes ansi the hagfishes represent an ancient, basal lineage. This hypothesis has essentially displaced the classical hypothesis of monophyly of the cyclostomes (lampreys plus hagfishes). To test these hypotheses, we compared nearly complete ribosomal DNA sequences from each of these major lineages, as well as those from a cephalochordate and a urochordate, which represent a paraphyletic outgroup for assessing the basal vertebrate relationships. For this comparison, 92%-99% complete 28S rDNA sequences were obtained from the lancelet Branchiostoma floridae, the hagfish Eptatretus stouti, the lamprey Petromyzon marinus, and cartilaginous fishes Hydrolagus colliei and Squalus acanthias and were then analyzed with previously reported 28S and 18S rDNA sequences from other chordates. We conducted conventional (nonparametric) bootstrap analyses, under maximum-likelihood, parsimony, and minimum-evolution (using LogDet distances) criteria, of both 28S and 18S rDNA sequences considered separately and combined. All these analyses provide moderate to very strong support for the monophyly of the cyclostomes. Furthermore, the currently accepted hypothesis of a lamprey-gnathostome clade is moderately rejected by the Kishino-Hasegawa test (P = 0.099) and resoundingly rejected by parametric bootstrap tests (P < 0.01) in favor of monophyly of living cyclostomes. Another significant finding is that the hagfish E. stouti has the longest 28S rDNA gene known in any organism (>5,200 nt).