Inverting the hourglass: quantitative evidence against the phylotypic stage in vertebrate development
Inverting the hourglass: quantitative evidence against the phylotypic stage in vertebrate development
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DOI：
10.1098/rspb.2002.2242
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发表时间：
2003-02-22
影响因子：
4.7
通讯作者：
Richardson, MK
中科院分区：
文献类型：
--
作者：
Bininda-Emonds, ORP;Jeffery, JE;Richardson, MK
当所有脊椎动物胚胎都表现出低表型多样性时，系统发育阶段的概念是现代发育生物学的重要基石。许多理论涉及发育模式、发育模块、发育机制（包括发育整合）以及自然选择对胚胎阶段的作用，已经参考系统发育阶段提出。然而，系统发育阶段从未被精确定义，也从未得到比较定量数据的最终支持或反驳。我们通过观察整个脊椎动物和哺乳动物内部的发育时间变异模式，定量测试了系统发育阶段的“发育沙漏”定义的预测。对于这两个数据集，使用两种不同指标的结果与定义的预测相反：物种之间的表型变异在发育序列的中间最高。这种令人惊讶的发育特征独立性程度反驳了脊椎动物系统发育阶段的存在。相反，我们假设在胚胎中期存在许多严格界定的发育模块。此外，这些模块之间的高水平时序变化（异时性）可能是导致脊椎动物多样性的重要进化机制。现在，系统发育阶段的支持者显然有责任提出其明确的定义和支持其存在的定量数据。
The concept of a phylotypic stage, when all vertebrate embryos show low phenotypic diversity, is an important cornerstone underlying modern developmental biology. Many theories involving patterns of development, developmental modules, mechanisms of development including developmental integration, and the action of natural selection on embryological stages have been proposed with reference to the phylotypic stage. However, the phylotypic stage has never been precisely defined, or conclusively supported or disproved by comparative quantitative data. We tested the predictions of the 'developmental hourglass' definition of the phylotypic stage quantitatively by looking at the pattern of developmental-timing variation across vertebrates as a whole and within mammals. For both datasets, the results using two different metrics were counter to the predictions of the definition: phenotypic variation between species was highest in the middle of the developmental sequence. This surprising degree of developmental character independence argues against the existence of a phylotypic stage in vertebrates. Instead, we hypothesize that numerous tightly delimited developmental modules exist during the mid-embryonic period. Further, the high level of timing changes (heterochrony) between these modules may be an important evolutionary mechanism giving rise to the diversity of vertebrates. The onus is now clearly on proponents of the phylotypic stage to present both a clear definition of it and quantitative data supporting its existence.