Donoghue Michael J
Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ, 85721.
Evolution. 1989 Sep;43(6):1137-1156. doi: 10.1111/j.1558-5646.1989.tb02565.x.
Studies of character evolution have frequently relied on ahistorical correlations rather than on phylogenies. However, correlations do not estimate the number of times that a trait evolved, and they are insensitive to the direction or the temporal sequence of character transformation. In contrast, cladograms can provide this information. A cladistic test of the hypothesis that the evolution of dioecy is favored in animal-dispersed plants indicates that dioecy may have originated somewhat more often in such lineages. Nevertheless, differences in rates of speciation or extinction must largely account for the observed species-level correlation between dispersal and breeding system. In considering the evolution of individual traits, cladograms help identify the context in which a feature evolved and specify which organisms should be compared in evaluating the causes of character change. Determining whether a feature and a performance advantage were strictly historically correlated or followed one another in sequence helps to distinguish whether the trait is an adaptation or an exaptation for the function. For example, cladograms of seed plants suggest that double fertilization arose incidentally prior to the origin of angiosperms and that the resulting product was later co-opted and elaborated as a nutritive tissue for the developing embryo. The order of character assembly in a lineage also bears on the evolution of functional and developmental interdependencies. In particular, it may be possible to trace the evolution of a character's "burden" from an initial period, during which change is more likely, through later stages, wherein successful modification is less likely owing to the evolution of dependent characters. The evolution of vessels and of floral phyllotaxis in angiosperms may exemplify this pattern. Recognition that the likelihood of character transformation may change during the evolution of a group warns against character weighting in phylogenetic analysis.
性状进化的研究常常依赖于非历史相关性而非系统发育关系。然而，相关性并不能估计一个性状进化的次数，而且它们对性状转变的方向或时间顺序不敏感。相比之下，分支图可以提供这些信息。对动物传播植物中雌雄异株进化受到青睐这一假设的分支检验表明，雌雄异株在这类谱系中的起源可能更为频繁。尽管如此，物种形成或灭绝速率的差异必须在很大程度上解释观察到的传播与繁殖系统之间的物种水平相关性。在考虑个体性状的进化时，分支图有助于确定一个特征进化的背景，并指明在评估性状变化原因时应比较哪些生物体。确定一个特征与性能优势是严格的历史相关还是依次出现，有助于区分该性状是对功能的适应还是预适应。例如，种子植物的分支图表明，双受精在被子植物起源之前偶然出现，其结果产物后来被采纳并发展成为发育中胚胎的营养组织。一个谱系中性状组合的顺序也与功能和发育相互依存关系的进化有关。特别是，有可能追溯一个性状“负担”的进化过程，从变化更可能发生的初始阶段，到由于相关性状的进化而成功修饰可能性较小的后期阶段。被子植物中导管和花的叶序的进化可能就是这种模式的例证。认识到在一个类群的进化过程中性状转变的可能性可能会发生变化，这提醒我们在系统发育分析中要避免对性状加权。
