Estimating metazoan divergence times with a molecular clock
Estimating metazoan divergence times with a molecular clock
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DOI：
10.1073/pnas.0401670101
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发表时间：
2004-04-27
影响因子：
11.1
通讯作者：
McPeek, MA
中科院分区：
文献类型：
--
作者：
Peterson, KJ;Lyons, JB;McPeek, MA
准确地确定第一个左右对称动物出现的时间对于我们理解早期动物进化至关重要。最早明确的两侧对称化石大约有5.55亿年的历史。相反，用脊椎动物化石记录校准的分子钟分析估计，脊椎动物大约在9亿年前（Ma）从双翅目（果蝇）分裂出来。尽管如此，比较基因组分析表明，脊椎动物和双翅目之间存在显着的差异，因为蚊子和苍蝇的基因组之间的百分比差异大于鱼类和小鼠之间的差异，即使脊椎动物的分歧几乎是双翅目的两倍。在这里，我们表明，双翅目的分子进化率是类似于其他无脊椎动物类群（棘皮动物和双壳类软体动物），但不是脊椎动物，这显着降低了他们的分子进化率相对于无脊椎动物。使用由来自23个组内分类群的7个不同氨基酸序列的串联组成的数据集（给出了分散在两侧动物树和整个中生代的11个不同的无脊椎动物校准点），我们估计两侧动物的最后一个共同祖先出现在573和656 Ma之间，这取决于分配给缩放分子取代速率异质性的参数的值。这些结果与已知的化石记录雅阁，并支持寒武纪大爆发部分反映了两侧动物门多样化的观点。
Accurately dating when the first bilaterally symmetrical animals arose is crucial to our understanding of early animal evolution. The earliest unequivocally bilaterian fossils are approximate to555 million years old. In contrast, molecular-clock analyses calibrated by using the fossil record of vertebrates estimate that vertebrates split from dipterans (Drosophila) approximate to900 million years ago (Ma). Nonetheless, comparative genomic analyses suggest that a significant rate difference exists between vertebrates and dipterans, because the percentage difference between the genomes of mosquito and fly is greater than between fish and mouse, even though the vertebrate divergence is almost twice that of the dipteran. Here we show that the dipteran rate of molecular evolution is similar to other invertebrate taxa (echinoderms and bivalve molluscs) but not to vertebrates, which significantly decreased their rate of molecular evolution with respect to invertebrates. Using a data set consisting of the concatenation of seven different amino acid sequences from 23 in-group taxa (giving a total of 11 different invertebrate calibration points scattered throughout the bilaterian tree and across the Phanerozoic), we estimate that the last common ancestor of bilaterians arose somewhere between 573 and 656 Ma, depending on the value assigned to the parameter scaling molecular substitution rate heterogeneity. These results are in accord with the known fossil record and support the view that the Cambrian explosion reflects, in part, the diversification of bilaterian phyla.