Drummond Alexei J, Ho Simon Y W, Phillips Matthew J, Rambaut Andrew
Department of Zoology, University of Oxford, Oxford, United Kingdom.
PLoS Biol. 2006 May;4(5):e88. doi: 10.1371/journal.pbio.0040088. Epub 2006 Mar 14.
In phylogenetics, the unrooted model of phylogeny and the strict molecular clock model are two extremes of a continuum. Despite their dominance in phylogenetic inference, it is evident that both are biologically unrealistic and that the real evolutionary process lies between these two extremes. Fortunately, intermediate models employing relaxed molecular clocks have been described. These models open the gate to a new field of "relaxed phylogenetics." Here we introduce a new approach to performing relaxed phylogenetic analysis. We describe how it can be used to estimate phylogenies and divergence times in the face of uncertainty in evolutionary rates and calibration times. Our approach also provides a means for measuring the clocklikeness of datasets and comparing this measure between different genes and phylogenies. We find no significant rate autocorrelation among branches in three large datasets, suggesting that autocorrelated models are not necessarily suitable for these data. In addition, we place these datasets on the continuum of clocklikeness between a strict molecular clock and the alternative unrooted extreme. Finally, we present analyses of 102 bacterial, 106 yeast, 61 plant, 99 metazoan, and 500 primate alignments. From these we conclude that our method is phylogenetically more accurate and precise than the traditional unrooted model while adding the ability to infer a timescale to evolution.
在系统发育学中,无根系统发育模型和严格分子钟模型是连续统一体的两个极端。尽管它们在系统发育推断中占据主导地位,但很明显这两者在生物学上都不现实,真正的进化过程介于这两个极端之间。幸运的是,已经描述了采用宽松分子钟的中间模型。这些模型为“宽松系统发育学”这一新领域打开了大门。在这里,我们介绍一种进行宽松系统发育分析的新方法。我们描述了在面对进化速率和校准时间的不确定性时,如何使用它来估计系统发育和分歧时间。我们的方法还提供了一种衡量数据集时钟相似性的手段,并在不同基因和系统发育之间比较这种度量。我们在三个大型数据集中未发现分支之间存在显著的速率自相关,这表明自相关模型不一定适用于这些数据。此外,我们将这些数据集置于严格分子钟和另一个无根极端之间的时钟相似性连续统一体上。最后,我们展示了对102个细菌、106个酵母、61个植物、99个后生动物和500个灵长类比对的分析。由此我们得出结论,我们的方法在系统发育上比传统的无根模型更准确、更精确,同时增加了推断进化时间尺度的能力。