Heard Stephen B
Department of Biological Sciences, University of Iowa, Iowa City, Iowa, 52242.
Evolution. 1996 Dec;50(6):2141-2148. doi: 10.1111/j.1558-5646.1996.tb03604.x.
Aspects of phylogenetic tree shape, and in particular tree balance, provide clues to the workings of the macroevolutionary process. I use a simulation approach to explore patterns in tree balance for several models of the evolutionary process under which speciation rates vary through the history of diversifying clades. I demonstrate that when speciation rates depend on an evolving trait of individuals, and are therefore "heritable" along evolutionary lineages, the resulting phylogenies become imbalanced. However, imbalance also results from some (but not all) models of "nonheritable" speciation rate variation. The degree of imbalance increases with the magnitude of speciation rate variation, and then for gradual evolution (but not punctuated equilibria) reaches an asymptote short of the theoretical maximum. Very high levels of rate variation are required to produce imbalance matching that found in real data (estimated phylogenies from the systematic literature). I discuss implications of the simulation results for our understanding of macroevolution.
系统发育树形状的各个方面，尤其是树的平衡性，为宏观进化过程的运作提供了线索。我采用模拟方法来探究多样化分支进化历史中物种形成速率变化的几种进化过程模型下的树平衡模式。我证明，当物种形成速率取决于个体的一个进化特征，因此沿着进化谱系是“可遗传的”时，所产生的系统发育树会变得不平衡。然而，不平衡也源于一些（但不是全部）“非可遗传的”物种形成速率变化模型。不平衡程度随着物种形成速率变化的幅度增加，然后对于渐进进化（但不是间断平衡）达到一个低于理论最大值的渐近线。需要非常高水平的速率变化才能产生与实际数据（从系统文献中估计的系统发育树）中发现的不平衡相匹配的情况。我讨论了模拟结果对我们理解宏观进化的意义。
