Bert Theresa M, McCarthy Kevin J, Cruz-Lopez Hector, Bogdanowicz Steven
Florida Marine Research Institute, 100 Eighth Avenue S.E., St., Petersburg, Florida, 33701.
Section of Ecology and Systematics, Corson Hall, Cornell University, Ithaca, New York, 14853.
Evolution. 1996 Apr;50(2):655-671. doi: 10.1111/j.1558-5646.1996.tb03876.x.
Many investigators categorize individuals from hybrid zones to facilitate comparisons among genotypic classes (e.g., parental, F , backcross) for comparative studies in which components of fitness or geographic variation are being analyzed. Frequently, multiple character sets representing genetically independent traits are used to classify these individuals and various methodologies are employed to combine the classifications obtained from the different character sets. We adapted the principles of total evidence and taxonomic congruence (two formalized approaches used by systematists in formulating phylogenetic hypotheses) to address the problem of discriminating hybridizing species and classifying individuals from hybrid zones. As our model, we used two morphological (coloration and morphometric) and two molecular (allozyme and mitochondrial DNA restriction-fragment-length polymorphism) character sets that differentiate two stone crab species (Menippe adina and M. mercenaria). Using principal-components analysis, we determined that combining character sets and eliminating characters or character sets that did not have large eigenvector coefficients for the principal component that best separated the two species yielded the highest level of discrimination between species and allowed us to classify a broad range of morpho-genotypes as hybrids. For the stone crabs, three diagnostic allozyme loci and five diagnostic coloration characters best separated the species. The two character sets were not completely congruent, but they agreed in their classification of 50% of the individuals from the hybrid zone and rarely strongly disagreed in their classifications. Classification discrepancies between the two character sets probably represent variation between traits in interspecific gene flow rather than intraspecific, ecologically mediated variation. Our results support the assertions of previous investigators who espoused the benefits associated with using multiple character sets to classify individuals from hybrid zones and demonstrate that, if character sets are reasonably congruent and numerically balanced, combining diagnostic characters from multiple character sets (a total-evidence approach) can enhance discriminatory power between species and facilitate the assignment of hybrid-zone individuals to genotypic classes. On the contrary, classifying hybrid-zone individuals using character sets separately (a taxonomic-congruence approach) provides the opportunity to compare levels of introgression between species and to assess reasons for discordance among the data sets.
许多研究人员对杂交区域的个体进行分类，以便在分析适合度或地理变异成分的比较研究中，促进基因型类别（如亲本、F1、回交）之间的比较。通常，代表遗传上独立性状的多个特征集用于对这些个体进行分类，并采用各种方法来合并从不同特征集获得的分类。我们采用了总证据原则和分类一致性原则（系统学家在构建系统发育假设时使用的两种形式化方法）来解决区分杂交物种和对杂交区域个体进行分类的问题。作为我们的模型，我们使用了两个形态学特征集（颜色和形态测量）和两个分子特征集（等位酶和线粒体DNA限制性片段长度多态性），这些特征集可以区分两种石蟹物种（Menippe adina和M. mercenaria）。通过主成分分析，我们确定，结合特征集并消除那些对于最能区分这两个物种的主成分没有大特征向量系数的特征或特征集，能够在物种之间产生最高水平的区分度，并使我们能够将广泛的形态基因型归类为杂种。对于石蟹来说，三个诊断性等位酶位点和五个诊断性颜色特征最能区分这两个物种。这两个特征集并不完全一致，但它们对杂交区域50%的个体分类达成了一致，并且在分类上很少出现强烈分歧。两个特征集之间的分类差异可能代表种间基因流中不同性状之间的变异，而不是种内生态介导的变异。我们的结果支持了先前研究人员的观点，他们主张使用多个特征集对杂交区域个体进行分类有诸多益处，并表明，如果特征集合理一致且在数值上平衡，结合多个特征集的诊断特征（一种总证据方法）可以增强物种之间的区分能力，并有助于将杂交区域个体归类到基因型类别中。相反，分别使用特征集对杂交区域个体进行分类（一种分类一致性方法），提供了比较物种间渗入水平并评估数据集之间不一致原因的机会。
