A Molecular Phylogenetic Perspective on Salamander Evolution

这项研究的目的是通过研究储存在它们的遗传物质(DNA)中的信息来揭示不同群体的火蜥蜴之间的进化关系。分别遗传的核DNA和线粒体DNA中包含的信息被用来提供不同种类火蜥蜴进化关系的两个独立推论。一群生物体的进化关系和历史多样性构成了理解该生物群的多样性、作为一种自然资源的价值和保护需求的基本知识。目前有九大类群被认为是分类学上的科(蛇形科、两形科、隐鳃科、双齿科、小蜥科、剑齿科、变形科、火蜥科和虎牙科)；该项目的早期结果表明，目前认识到的双齿科错误地归入了两个非常不同的进化谱系。火蜥蜴家族之间的进化关系以及每个家族中包含的主要谱系的关系构成了这项工作的重点。实验程序包括从标本中提纯DNA，分离出可比较的(同源的)DNA片段，获得这些DNA片段的核苷酸序列，并使用统计检验来区分火蜥蜴进化的替代假说。然后，物种间的关系模式被用来调查在每一组中观察到的生物多样性产生的过程，并特别关注发育模式。火蜥蜴家族之间的进化关系被用来研究幼虫繁殖的进化，这种进化在火蜥蜴中发生过多次。Plethodontidae和Salamandridae之间的进化关系解决了在这些家庭中观察到的多样化、专门化摄食机制的进化。这项分析的所有层面都有助于对火蜥蜴进行修订的分类。这项工作还揭示了所研究的核和线粒体DNA序列的进化特性。特别注意评估分子进化模式是否满足用于从DNA序列比较中获得进化信息的分析方法的假设。这一结果提供了关于使用的最佳分析方法以及进化分歧时间的大小的一般信息，这些分子比较将在这些时间内提供信息。这有助于使用分子序列比较来对其他生物体群体进行类似的研究。

The purpose of this research is to reveal the evolutionary relationships among the different groups of salamanders by studying the information stored in their genetic material (DNA). Information contained in the separately inherited nuclear DNA and mitochondrial DNA is used to provide two independent inferences of the evolutionary relationships of the different groups of salamander. The evolutionary relationships and historical diversification of a group of organisms constitute essential knowledge for understanding the group's diversity, value as a natural resource and need for conservation. Nine major groups of salamanders are currently recognized as taxonomic families (Ambystomatidae, Amphiumidae, Cryptobranchidae, Dicamptodontidae, Hynobiidae, Plethodontidae, Proteidae, Salamandridae and Sirenidae); earlier results of this project suggest that the Dicamptodontidae as currently recognized incorrectly groups two very different evolutionary lineages. The evolutionary relationships of the salamander families to each other and the relationships of the major lineages contained within each family constitute the focus of this work. The experimental procedure consists of purifying DNA from specimens, isolating comparable ("homologous") segments of DNA, obtaining the nucleotide sequence of those DNA segments, and using statistical tests to discriminate alternative hypothesis of salamander evolution. The patterns of relationship among species are then used to investigate the processes by which the organismal diversity observed in each group arose, giving special attention to developmental patterns. Evolutionary relationships among the salamander families are used to investigate the evolution of larval reproduction, which has occurred multiple times in salamanders. Evolutionary relationships within the Plethodontidae and Salamandridae address the evolution of the diverse, specialized feeding mechanisms that are observed in these families. All levels of this analysis contribute to a revised taxonomic classification of the salamanders. This work also reveals the evolutionary properties of the nuclear and mitochondrial DNA sequences studied. Particular attention is given to evaluating whether the molecular evolutionary pattern meets the assumptions of the analytical methods used to obtain evolutionary information from DNA sequence comparisons. This result provides general information regarding the best analytical methods to use and the magnitude of evolutionary divergence times over which these molecular comparisons will be informative. This facilitates the use of molecular sequence comparisons for conducting similar studies on other groups of organisms.