Sanderson Michael J, Donoghue Michael J
Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ, 85721.
Evolution. 1989 Dec;43(8):1781-1795. doi: 10.1111/j.1558-5646.1989.tb02626.x.
Patterns of variation in levels of homoplasy were explored through statistical analyses of standardized consistency indexes. Data were obtained from 60 recent cladistic analyses of a wide variety of organisms based on several different kinds of characters. Consistency index is highly correlated with the number of taxa included in an analysis, with homoplasy increasing as the number of taxa increases. This observation is compatible with a simple model of character evolution in which 1) the probability of character-state change increases with the total number of branches in a tree and 2) the number of possible states of a character is limited. Consistency index does not show a significant relationship to the number of characters utilized in an analysis or to the taxonomic rank of the terminal taxa. When the relationship between consistency index and number of taxa is taken into account, there is no significant difference between plant and animal data sets in the amount of homoplasy. Likewise, the level of homoplasy in morphological and molecular data sets does not appear to differ significantly, although there are still too few molecular studies to be confident of this result. Future comparisons of consistency indexes, including studies along the lines established here, must take into account the influence of the number of taxa on homoplasy.
通过对标准化一致性指数的统计分析，探究了同塑性水平的变化模式。数据取自基于几种不同特征对多种生物进行的60项近期分支系统学分析。一致性指数与分析中包含的分类单元数量高度相关，随着分类单元数量的增加，同塑性也会增加。这一观察结果与一个简单的性状进化模型相符，在该模型中：1）性状状态变化的概率随着树中分支总数的增加而增加；2）性状的可能状态数量是有限的。一致性指数与分析中使用的性状数量或终端分类单元的分类等级没有显著关系。当考虑一致性指数与分类单元数量之间的关系时，植物和动物数据集在同塑性程度上没有显著差异。同样，形态学和分子数据集的同塑性水平似乎也没有显著差异，尽管分子研究仍然太少，无法确定这一结果。未来对一致性指数的比较，包括按照此处确立的思路进行的研究，必须考虑分类单元数量对同塑性的影响。
