Steppan Scott J
Committee on Evolutionary Biology, The University of Chicago, Chicago, Illinois, 60637.
Division of Mammals, The Field Museum, Chicago, Illinois, 60605.
Evolution. 1997 Apr;51(2):587-594. doi: 10.1111/j.1558-5646.1997.tb02445.x.
A modified minimum evolution approach is used to estimate covariance matrices for hypothetical ancestors. Branch lengths are calculated as the mean disparity in corresponding ancestor-descendent covariances. Branches are longest leading to terminal populations and subspecies, while interspecific branches are relatively short, indicating a general conservation of covariance structure among species despite a high degree of intraspecific variability. Absolute deviations in covariance structure are not correlated with phenotypic divergence. Interpreted in light of other studies, the analyses suggest that deviations in covariance structure are most strongly associated with the formation of diagnosably distinct taxa and stochastic sampling of genotypes at the population level. There is no evidence for restructuring of phenotypic covariance structure in association with reproductive isolation. The results suggest that phenotypic covariances are dynamic over short time scales and do not support attempts to extrapolate genetic covariance structure to explain or predict macroevolutionary change. This study further demonstrates that branch lengths, which are not usually analyzed in detail, contain valuable evolutionary information complementary to that residing in the branching pattern.
一种改进的最小进化方法用于估计假设祖先的协方差矩阵。分支长度计算为相应祖先 - 后代协方差中的平均差异。通向终端种群和亚种的分支最长，而种间分支相对较短，这表明尽管种内变异性很高，但物种间协方差结构总体上是保守的。协方差结构的绝对偏差与表型差异无关。根据其他研究解释，分析表明协方差结构的偏差与可诊断的不同分类群的形成以及种群水平上基因型的随机抽样最密切相关。没有证据表明表型协方差结构的重组与生殖隔离有关。结果表明，表型协方差在短时间尺度上是动态的，不支持外推遗传协方差结构来解释或预测宏观进化变化的尝试。这项研究进一步表明，通常未详细分析的分支长度包含与分支模式中所包含的信息互补的有价值的进化信息。
