Schluter Dolph, Price Trevor, Mooers Arne Ø, Ludwig Donald
Department of Zoology and Centre for Biodiversity Research, University of British Columbia, Vancouver, British Columbia, V6T 1Z4, Canada.
Biology Department O-116, University of California-San Diego, La Jolla, California, 92093.
Evolution. 1997 Dec;51(6):1699-1711. doi: 10.1111/j.1558-5646.1997.tb05095.x.
Theories of ecological diversification make predictions about the timing and ordering of character state changes through history. These theories are testable by "reconstructing" ancestor states using phylogenetic trees and measurements of contemporary species. Here we use maximum likelihood to estimate and evaluate the accuracy of ancestor reconstructions. We present likelihoods of discrete ancestor states and derive probability distributions for continuous ancestral traits. The methods are applied to several examples: diets of ancestral Darwin's finches; origin of inquilinism in gall wasps; microhabitat partitioning and body size evolution in scrubwrens; digestive enzyme evolution in artiodactyl mammals; origin of a sexually selected male trait, the sword, in platies and swordtails; and evolution of specialization in Anolis lizards. When changes between discrete character states are rare, the maximum-likelihood results are similar to parsimony estimates. In this case the accuracy of estimates is often high, with the exception of some nodes deep in the tree. If change is frequent then reconstructions are highly uncertain, especially of distant ancestors. Ancestor states for continuous traits are typically highly uncertain. We conclude that measures of uncertainty are useful and should always be provided, despite simplistic assumptions about the probabilistic models that underlie them. If uncertainty is too high, reconstruction should be abandoned in favor of approaches that fit different models of trait evolution to species data and phylogenetic trees, taking into account the range of ancestor states permitted by the data.
生态多样化理论对性状状态随时间变化的时间和顺序做出了预测。这些理论可以通过利用系统发育树和当代物种的测量数据“重建”祖先状态来进行检验。在这里，我们使用最大似然法来估计和评估祖先重建的准确性。我们给出了离散祖先状态的似然值，并推导出连续祖先性状的概率分布。这些方法被应用于几个例子：达尔文雀祖先的食性；瘿蜂 inquilinism 的起源；灌丛鹩的微生境划分和体型进化；偶蹄目哺乳动物消化酶的进化；食蚊鱼和剑尾鱼中一种性选择的雄性特征——剑的起源；以及安乐蜥的特化进化。当离散性状状态之间的变化很少见时，最大似然结果与简约估计相似。在这种情况下，估计的准确性通常较高，但树中一些深层节点除外。如果变化频繁，那么重建就高度不确定，尤其是对遥远祖先的重建。连续性状的祖先状态通常也高度不确定。我们得出结论，不确定性度量是有用的，并且应该始终提供，尽管其基于的概率模型存在简单化假设。如果不确定性过高，就应该放弃重建，转而采用将不同性状进化模型与物种数据和系统发育树相拟合的方法，同时考虑数据所允许的祖先状态范围。
