Graduate Program in Organismic and Evolutionary Biology, University of Massachusetts Amherst, Amherst, Massachusetts.
Department of Biology, University of Washington, Seattle, Washington.
Evolution. 2019 Oct;73(10):2060-2071. doi: 10.1111/evo.13815. Epub 2019 Aug 19.
Mammals flex, extend, and rotate their spines as they perform behaviors critical for survival, such as foraging, consuming prey, locomoting, and interacting with conspecifics or predators. The atlas-axis complex is a mammalian innovation that allows precise head movements during these behaviors. Although morphological variation in other vertebral regions has been linked to ecological differences in mammals, less is known about morphological specialization in the cervical vertebrae, which are developmentally constrained in number but highly variable in size and shape. Here, we present the first phylogenetic comparative study of the atlas-axis complex across mammals. We used spherical harmonics to quantify 3D shape variation of the atlas and axis across a diverse sample of species, and performed phylogenetic analyses to investigate if vertebral shape is associated with body size, locomotion, and diet. We found that differences in atlas and axis shape are partly explained by phylogeny, and that mammalian subclades differ in morphological disparity. Atlas and axis shape diversity is associated with differences in body size and locomotion; large terrestrial mammals have craniocaudally elongated vertebrae, whereas smaller mammals and aquatic mammals have more compressed vertebrae. These results provide a foundation for investigating functional hypotheses underlying the evolution of neck morphologies across mammals.
哺乳动物在进行觅食、捕食、移动和与同类或捕食者互动等生存关键行为时，会弯曲、伸展和旋转脊柱。寰枢复合体是哺乳动物的一项创新，允许在这些行为中进行精确的头部运动。尽管其他脊椎区域的形态变异与哺乳动物的生态差异有关，但对颈椎的形态特化知之甚少，颈椎在数量上受到发育限制，但在大小和形状上高度可变。在这里，我们首次对哺乳动物的寰枢复合体进行了系统发育比较研究。我们使用球谐函数来量化不同物种的寰枢椎的 3D 形态变化，并进行了系统发育分析，以研究椎体形状是否与体型、运动和饮食有关。我们发现，寰枢椎形状的差异部分可以用系统发育来解释，而且哺乳动物的亚类在形态差异上也存在差异。寰枢椎的形状多样性与体型和运动方式的差异有关；大型陆生哺乳动物的脊椎具有头尾拉长的形状，而较小的哺乳动物和水生哺乳动物的脊椎则更为压缩。这些结果为研究哺乳动物颈部形态进化的功能假说提供了基础。
