Replaying evolutionary transitions from the dental fossil record

摘要

The evolutionary relationships of extinct species are ascertained primarily through the analysis of morphological characters. Character inter-dependencies can have a substantial effect on evolutionary interpretations, but the developmental underpinnings of character inter-dependence remain obscure because experiments frequently do not provide detailed resolution of morphological characters. Here we show experimentally and computationally how gradual modification of development differentially affects characters in the mouse dentition. We found that intermediate phenotypes could be produced by gradually adding ectodysplasin A (EDA) protein in culture to tooth explants carrying a null mutation in the tooth-patterning gene Eda. By identifying development-based character inter-dependencies, we show how to predict morphological patterns of teeth among mammalian species.Finally , in vivo inhibition of sonic hedgehog signalling in Eda null teeth enabled us to reproduce characters deep in the rodent ancestry. Taken together, evolutionarily informative transitions can be experimentally reproduced, thereby providing development -based expectations for character-state transitions used in evolutionary studies.%演化传统上呈现为一系列成年形态,反映它们随时间所发生的变化,而牙齿则经常是古生物学家可以利用的最好(或惟一)证据。牙齿特征因此被广泛用来确定化石物种的相关性。现在,Jukka Jernvall及同事采用发育生物学方法来重现啮齿类动物牙齿过去5,000万年的演化。不能产生形态发生素"外异蛋白"的小鼠有非常一般化的牙齿。向突变牙齿外植体中添加少量"外异蛋白",会重现啮齿类动物牙齿的形态随时间推移已知所发生的变化。作者建立了一个关于牙齿发育的计算模型,该模型有—个界面(ToothMaker),它为弄清物种之间的关系提供了一个新工具。