Douady Christophe J, Dosay Miné, Shivji Mahmood S, Stanhope Michael J
Department of Biochemistry and Molecular Biology, Dalhousie University, 5859 University Avenue, Halifax, Nova Scotia, Canada B3H 4H7.
Mol Phylogenet Evol. 2003 Feb;26(2):215-21. doi: 10.1016/s1055-7903(02)00333-0.
Early morphological studies regarding the evolutionary history of elasmobranchs suggested sharks and batoids (skates and rays) were respectively monophyletic. More modern morphological cladistic studies, however, have tended to suggest that batoids are derived sharks, closely related to sawsharks and angelsharks, a phylogenetic arrangement known as the Hypnosqualea hypothesis. Very few molecular studies addressing interordinal relationships of elasmobranchs have been published; the few that do exist, are very limited in terms of both taxon representation and/or aligned sequence positions, and are insufficient to answer the question of whether batoids are derived sharks. The purpose of this study was to address this issue with more complete taxon representation, concomitant with a reasonable number of aligned sequence positions. The data set included a 2.4-kb segment of the mitochondrial 12S rRNA-tRNA valine-16S rRNA locus, and in terms of taxa, representatives of two orders of Batoidea, at least one representative of all orders of sharks, and as an outgroup, the widely recognized sister group to elasmobranchs-Holocephali. The results provide the first convincing molecular evidence for shark monophyly and the rejection of the Hypnosqualea hypothesis. Our phylogenetic placement of batoids as a basal elasmobranch lineage means that much of the current thinking regarding the evolution of morphological and life history characteristics in elasmobranchs needs to be re-evaluated.
早期关于板鳃亚纲动物进化史的形态学研究表明，鲨鱼和鳐魟类（鳐和魟）分别是单系类群。然而，更现代的形态学分支系统学研究倾向于表明，鳐魟类是衍生的鲨鱼，与锯鲨和扁鲨关系密切，这种系统发育排列被称为Hypnosqualea假说。很少有关于板鳃亚纲动物目间关系的分子研究发表；现有的少数研究在分类单元代表性和/或比对序列位置方面都非常有限，不足以回答鳐魟类是否是衍生鲨鱼的问题。本研究的目的是通过更完整的分类单元代表性，并结合合理数量的比对序列位置来解决这个问题。数据集包括线粒体12S rRNA - tRNA缬氨酸 - 16S rRNA基因座的一个2.4千碱基片段，在分类单元方面，包括两个鳐魟目代表、所有鲨鱼目的至少一个代表，以及作为外类群的、被广泛认可的板鳃亚纲动物的姐妹类群——全头亚纲。结果为鲨鱼的单系性提供了首个令人信服的分子证据，并否定了Hypnosqualea假说。我们将鳐魟类置于板鳃亚纲基部谱系的系统发育位置意味着，目前许多关于板鳃亚纲动物形态和生活史特征进化的观点需要重新评估。
