Ortí G, Meyer A
Department of Ecology and Evolution, State University of New York, Stony Brook, New York 11794-5245, USA.
Syst Biol. 1997 Mar;46(1):75-100. doi: 10.1093/sysbio/46.1.75.
Phylogenetic relationships among fishes from ostariophysan orders, characiform families, and serrasalmin genera (e.g., "piranhas") were examined using partial mitochondrial ribosomal DNA sequences of the 12S and 16S genes. Phylogenetic information content of these sequences was assessed at three levels of taxonomic inclusiveness by analyzing the patterns of nucleotide substitution using secondary structure models. Conserved and variable regions were identified, mapped onto the structural models, and compared at increasing levels of taxonomic divergence. In general, loop regions (unpaired) exhibited a higher level of variation than did stem regions (paired). A high proportion of compensatory substitutions was observed in stem regions in three data sets, suggesting strong selection to maintain the secondary structure. Saturation due to multiple substitutions was indicated by decreasing transition/transversion ratios and strong structural constraints on variation in comparisons among orders of Ostariophysi but was not obvious among families of Characiformes and was not detected among serrasalmin genera. Reliable phylogenetic signal successfully reconstructed relationships among serrasalmin genera. However, aside from a few well-supported clades, relationships could not be reconstructed with confidence among characiform families and ostariophysan orders. The reciprocal monophyly of African and Neotropical characiform lineages was rejected (based on maximum likelihood ratio tests), and some support for previous hypotheses based on morphology was provided by the molecular data. The radiation of characiform fishes is discussed in a historical biogeographic context.
利用12S和16S基因的部分线粒体核糖体DNA序列，研究了骨鳔总目鱼类、脂鲤科鱼类和锯脂鲤属（如“食人鱼”）之间的系统发育关系。通过使用二级结构模型分析核苷酸替换模式，在三个分类包容性水平上评估了这些序列的系统发育信息含量。识别出保守区和可变区，将其映射到结构模型上，并在分类分歧程度不断增加的情况下进行比较。一般来说，环区（未配对）比茎区（配对）表现出更高的变异水平。在三个数据集中，茎区观察到高比例的补偿性替换，表明存在强烈的选择以维持二级结构。由于多次替换导致的饱和度通过转换/颠换比率的降低以及骨鳔总目各目之间比较中对变异的强烈结构限制来表明，但在脂鲤科各属之间不明显，在锯脂鲤属中未检测到。可靠的系统发育信号成功重建了锯脂鲤属之间的关系。然而，除了少数得到充分支持的分支外，脂鲤科各属之间以及骨鳔总目各目之间的关系无法可靠地重建。非洲和新热带脂鲤科谱系的相互单系性被拒绝（基于最大似然比检验），分子数据为先前基于形态学的假设提供了一些支持。在历史生物地理学背景下讨论了脂鲤科鱼类的辐射。
