Department of Anthropology, University of Toronto Scarborough, Toronto, ON M1C 1A4, Canada
Department of Anthropology, University of Toronto Scarborough, Toronto, ON M1C 1A4, Canada.
Proc Natl Acad Sci U S A. 2021 Jan 5;118(1). doi: 10.1073/pnas.2008850118. Epub 2020 Dec 21.
Identifying developmental explanations for the evolution of complex structures like mammalian molars is fundamental to studying phenotypic variation. Previous study showed that a "morphogenetic gradient" of molar proportions was explained by a balance between inhibiting/activating activity from earlier developing molars, termed the inhibitory cascade model (ICM). Although this model provides an explanation for variation in molar proportions, what remains poorly understood is if molar shape, or specifically complexity (i.e., the number of cusps, crests), can be explained by the same developmental model. Here, we show that molar complexity conforms to the ICM, following a linear, morphogenetic gradient along the molar row. Moreover, differing levels of inhibiting/activating activity produce contrasting patterns of molar complexity depending on diet. This study corroborates a model for the evolution of molar complexity that is developmentally simple, where only small-scale developmental changes need to occur to produce change across the entire molar row, with this process being mediated by an animal's ecology. The ICM therefore provides a developmental framework for explaining variation in molar complexity and a means for testing developmental hypotheses in the broader context of mammalian evolution.
确定哺乳动物牙齿等复杂结构进化的发育解释对于研究表型变异至关重要。先前的研究表明，一种称为抑制级联模型（ICM）的早期发育牙齿的抑制/激活活性之间的平衡解释了摩尔比例的“形态发生梯度”。尽管该模型为摩尔比例的变化提供了解释，但仍然不清楚摩尔形状，或者更具体地说，复杂性（即，尖峰，嵴的数量）是否可以用相同的发育模型来解释。在这里，我们表明，摩尔复杂性符合 ICM，沿着摩尔行呈线性形态发生梯度。此外，不同水平的抑制/激活活性会根据饮食产生不同的摩尔复杂性模式。这项研究证实了一个关于摩尔复杂性进化的模型，该模型在发育上很简单，只需发生小规模的发育变化即可在整个摩尔行中产生变化，而这个过程是由动物的生态介导的。因此，ICM 为解释摩尔复杂性的变化提供了一个发育框架，并为在哺乳动物进化的更广泛背景下测试发育假设提供了一种手段。
