Reconciling Molecular and Fossil Evidence on the Age of Angiosperms

9726856桑德森被子植物的年龄长期以来一直是植物进化论中有争议的话题。传统上，这个问题主要是从古植物学的角度来解决的。然而，依赖于恒定进化速度假说(“分子钟”)的分子研究为这个问题增加了一个新的维度，通常表明的年龄比化石证据要老得多。其中许多分析相互矛盾，因此它们不仅质疑古植物学假设，而且质疑分子时钟的有效性，这是分子进化中的一个主要问题。桑德森博士和道尔博士将利用新的数据和新的分析方法，对分子证据对被子植物年龄的影响进行关键评估，特别是它与化石证据的一致或不一致。他们建议将来自rbcL、atpB和18S rDNA基因的现有和新的序列数据与从四个缓慢进化的叶绿体基因获得的新数据相结合。分类群的取样将侧重于具有良好白垩纪化石记录的被子植物，或代表被子植物树中早期分支的被子植物以及其他相关种子植物。使用允许假设进化速度不同的新方法，我们希望获得更好的评估(1)被子植物年龄的分子估计的误差和这些误差的来源，以及(2)当考虑到分歧时间的误差时，被子植物年龄的化石证据和分子估计之间的不一致程度。从这项研究中得出的方法和见解可能有助于对分子数据和化石数据之间存在明显冲突的其他群体进行年代测定。

9726856 Sanderson The age of the angiosperms has long been a topic of controversy in plant evolution. Traditionally, the problem was addressed primarily from a paleobotanical point of view. However, molecular studies relying on the hypothesis of a constant rate of evolution ("molecular clock") have added a new dimension to the problem, often suggesting a much older age than does fossil evidence. Many of these analyses conflict with each other, and therefore they call into question not only paleobotanical assumptions but also the validity of the molecular clock, a major issue in molecular evolution. Drs. Sanderson and Doyle will undertake a critical evaluation of the implications of molecular evidence for the age of angiosperms, especially its agreement or disagreement with fossil evidence, using both new data and new methods of analysis. They propose to combine existing and new sequence data from rbcL, atpB, and 18S rDNA genes with new data to be obtained from four slowly evolving chloroplast genes. Sampling of taxa will emphasize angiosperms with a good Cretaceous fossil record or which represent early branches in the angiosperm tree in addition to other relevant seed plants. Using new methodologies that allow hypothetical rates of evolution to vary, we hope to obtain a better assessment of (1) the error in molecular estimates of the age of angiosperms and the sources of those errors, and (2) the level of disagreement between fossil evidence for the age of angiosperms and molecular estimates when the error in divergence times is taken into account. Methods and insights derived from this study may be useful in dating other groups where there are apparent conflicts between molecular and fossil data.