Data from: Mind the gap: genetic manipulation of basicranial growth within synchondroses modulates calvarial and facial shape in mice through epigenetic interactions

Phenotypic integration patterns in the mammalian skull have long been a focus of intense interest as a result of their suspected influence on the trajectory of hominid evolution. Here we test the hypothesis that perturbation of cartilage growth, which directly affects only the chondrocranium during development, will produce coordinated shape changes in the adult calvarium and face regardless of mechanism. Using two murine models of cartilage undergrowth that target two very different mechanisms, we show that strong reduction in cartilage growth produces a short, wide, and more flexed cranial base. This in turn produces a short, wide face in both models. Cranial base and face are already correlated early in ontogeny, and the relationship between these modules gains structure through postnatal growth and development. These results provide further evidence that there exist physical interactions between developing parts of the phenotype that produce variation at a distance from the actual locus upon which a particular selective pressure is acting. Phenotypic changes observed over the course of evolution may not all require adaptationist explanations; rather, it is likely that a substantial portion of observed phenotypic variation over the history of a clade is not directly adaptive but rather a secondary consequence of some local response to selection.

哺乳动物颅骨的表型整合（phenotypic integration）模式，因其被推测会影响人科演化轨迹，长期以来一直是学界高度关注的研究热点。本研究验证了下述假说：发育过程中仅直接作用于软骨颅（chondrocranium）的软骨生长扰动，无论其作用机制如何，均可导致成年个体颅盖骨（calvarium）与面部产生协同的形状变化。我们采用两种靶向完全不同作用机制的小鼠软骨发育不全模型开展实验，结果显示软骨生长的显著抑制会形成短宽且曲度更大的颅底（cranial base）结构，进而使两种模型的面部均呈现短宽形态。颅底与面部在个体发育（ontogeny）早期就已存在相关性，且二者的关联关系会在出生后的生长发育过程中逐步完善结构特征。本研究结果进一步证实，表型发育的不同组分之间存在物理相互作用，这种相互作用会产生与特定选择压力（selective pressure）实际作用位点存在空间距离的表型变异。演化过程中观测到的表型变化并非都需要适应主义解释；实际上，在一个演化支（clade）的演化历史中观测到的大量表型变异可能并非直接受选择作用，而是局部选择响应所带来的次级后果。