National Evolutionary Synthesis Center, Durham, NC 27705, USA
Department of Biology, Rutgers University, Newark, NJ 07102, USA American Museum of Natural History, Division of Invertebrate Zoology, 79th and Central Park West, New York, NY 10024, USA.
Proc Biol Sci. 2014 Aug 7;281(1788):20140677. doi: 10.1098/rspb.2014.0677.
Major disparities are recognized between molecular divergence dates and fossil ages for critical nodes in the Tree of Life, but broad patterns and underlying drivers remain elusive. We harvested 458 molecular age estimates for the stem and crown divergences of 67 avian clades to explore empirical patterns between these alternate sources of temporal information. These divergence estimates were, on average, over twice the age of the oldest fossil in these clades. Mitochondrial studies yielded older ages than nuclear studies for the vast majority of clades. Unexpectedly, disparity between molecular estimates and the fossil record was higher for divergences within major clades (crown divergences) than divergences between major clades (stem divergences). Comparisons of dates from studies classed by analytical methods revealed few significant differences. Because true divergence ages can never be known with certainty, our study does not answer the question of whether fossil gaps or molecular dating error account for a greater proportion of observed disparity. However, empirical patterns observed here suggest systemic overestimates for shallow nodes in existing molecular divergence dates for birds. We discuss underlying biases that may drive these patterns.
在生命之树的关键节点上，分子分歧日期和化石年龄之间存在显著差异，但广泛的模式和潜在的驱动因素仍然难以捉摸。我们收集了 67 个鸟类进化枝的主干和冠部分歧的 458 个分子年龄估计值，以探讨这些替代时间信息源之间的经验模式。这些分歧估计值平均比这些进化枝中最古老的化石年龄大两倍以上。对于绝大多数进化枝来说，线粒体研究的年龄比核研究的年龄大。出乎意料的是，分子估计值与化石记录之间的差异在主要进化枝（冠部分歧）内的分歧比主要进化枝之间（主干分歧）的分歧更高。对按分析方法分类的研究的日期进行比较，发现很少有显著差异。由于真正的分歧年龄永远无法确定，因此我们的研究并不能回答化石空白或分子定年误差是否占观察到的差异更大比例的问题。然而，这里观察到的经验模式表明，鸟类现有分子分歧日期中浅层节点存在系统高估。我们讨论了可能导致这些模式的潜在偏差。
