Shaul Shaul, Graur Dan
Department of Zoology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Israel.
Gene. 2002 Oct 30;300(1-2):59-61. doi: 10.1016/s0378-1119(02)00851-x.
For any given taxonomic divergence event, one may find in the literature a wide range of time estimates. Many factors contribute to the variation in molecular date estimates for the same evolutionary event. High on the list is the choice of calibration points for converting genetic distances into evolutionary rates and, subsequently, into dates of divergence. In this study, we investigate one critical source of error in estimating divergence times, i.e. the use of secondary calibration points, which are divergence time estimates that have been derived from one molecular dataset on the basis of a primary external calibration point, and which are used again independently of the original external calibration point on a second dataset. Unless particular care is exercised, this practice leads to internal inconsistencies, and the inferred dates of divergence are by necessity unreliable. We present a consistency test for assessing the reliability of divergence time estimates based on secondary calibration points. As a case study, we examine recent estimates of divergence times among phyla and kingdoms based on multiple nuclear protein-coding genes, and show that they fail the consistency test.
对于任何给定的分类学分歧事件，人们可能会在文献中找到各种各样的时间估计值。许多因素导致了同一进化事件分子日期估计的差异。其中最重要的是校准点的选择，校准点用于将遗传距离转换为进化速率，进而转换为分歧日期。在本研究中，我们调查了估计分歧时间时一个关键的误差来源，即使用二级校准点，二级校准点是基于主要外部校准点从一个分子数据集得出的分歧时间估计值，并且在第二个数据集上独立于原始外部校准点再次使用。除非格外小心，这种做法会导致内部不一致，并且推断出的分歧日期必然不可靠。我们提出了一种一致性检验，用于评估基于二级校准点的分歧时间估计的可靠性。作为一个案例研究，我们研究了基于多个核蛋白编码基因对门和界之间分歧时间的最新估计，并表明它们未通过一致性检验。
