Molecular Dating, Evolutionary Rates, and the Age of the Grasses
Molecular Dating, Evolutionary Rates, and the Age of the Grasses
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DOI：
10.1093/sysbio/syt072
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发表时间：
2014-03-01
影响因子：
6.5
通讯作者：
Edwards, Erika J.
中科院分区：
文献类型：
--
作者：
Christin, Pascal-Antoine;Spriggs, Elizabeth;Edwards, Erika J.
进化生物学中的许多问题都需要估计分歧时间，但对于化石记录稀少的群体来说，这种估计在很大程度上依赖于分子测年方法。这些方法的准确性取决于一个足够的基础模型和化石证据作为校准点的适当实施。我们探讨这些在禾本科（草），一个非常有限的化石记录，特别是集中在约会组的早期分歧的多样化的植物谱系的影响。我们表明，分子测年的基础上的质体标记物的数据集是强烈依赖于模型的假设。特别是，加速的进化速率在该基地的禾本科，然后在后代的减速强烈偏见的方法，假设自相关率。这个问题可以通过使用具有较低速率变化的标记来规避，并且我们表明，从完整的核基因组中提取的系统发育标记可以是更常用的质体标记的有用补充。然而，分歧时间的估计仍然受到化石校准点的不同实现的强烈影响。仅用大型化石校准的分析导致禾本科核心的年龄估计为51-55 Ma，但包含微体化石证据将这一年龄推高到74-82 Ma，并导致估计的禾本科进化速率较低。这些结果强调了在解决依赖于重要群体估计年龄的进化问题时，考虑来自多个基因组和替代化石位置的标记的重要性。
Many questions in evolutionary biology require an estimate of divergence times but, for groups with a sparse fossil record, such estimates rely heavily on molecular dating methods. The accuracy of these methods depends on both an adequate underlying model and the appropriate implementation of fossil evidence as calibration points. We explore the effect of these in Poaceae (grasses), a diverse plant lineage with a very limited fossil record, focusing particularly on dating the early divergences in the group. We show that molecular dating based on a data set of plastid markers is strongly dependent on the model assumptions. In particular, an acceleration of evolutionary rates at the base of Poaceae followed by a deceleration in the descendants strongly biases methods that assume an autocorrelation of rates. This problem can be circumvented by using markers that have lower rate variation, and we show that phylogenetic markers extracted from complete nuclear genomes can be a useful complement to the more commonly used plastid markers. However, estimates of divergence times remain strongly affected by different implementations of fossil calibration points. Analyses calibrated with only macrofossils lead to estimates for the age of core Poaceae similar to 51-55 Ma, but the inclusion of microfossil evidence pushes this age to 74-82 Ma and leads to lower estimated evolutionary rates in grasses. These results emphasize the importance of considering markers from multiple genomes and alternative fossil placements when addressing evolutionary issues that depend on ages estimated for important groups.