Department of Anthropology, Buffalo Human Evolutionary Morphology Lab, University at Buffalo, Buffalo, NY, USA.
Department of Anthropology, University of Oregon, Eugene, OR, USA.
J Anat. 2021 Mar;238(3):693-710. doi: 10.1111/joa.13331. Epub 2020 Oct 20.
In studies of ontogenetic allometry, ontogenetic scaling has often been invoked to explain cranial morphological differences between smaller and larger forms of closely related taxa. These scaled variants in shape have been hypothesized to be the result of the extension or truncation of common growth allometries. In this scenario, change in size is the determining factor, perhaps under direct selection, and changes in cranial shapes are byproducts, not under direct selection themselves. However, many of these conclusions are based on studies that used bivariate generalizations of shape. Even among multivariate analyses of growth allometries, there are discrepancies as to the prevalence of ontogenetic scaling among primates, how shared the trajectories need to be, and which taxa evince properties of scaled variants. In this investigation, we use a large, comparative ontogenetic sample, geometric morphometric methods, and multivariate statistical tests to examine ontogenetic allometry and evaluate if differences in cranial shape among closely related catarrhines of varying sizes are primarily driven by size divergence, that is, ontogenetic scaling. We then evaluate the hypothesis of size as a line of least evolutionary resistance in catarrhine cranial evolution. We found that patterns of ontogenetic allometry vary among taxa, indicating that ontogenetic scaling sensu stricto does not often account for most morphological differences and that large and small taxa within clades are generally not scaled variants. The presence of a variety of ontogenetic pathways for the evolution of cranial shapes provides indirect evidence for selection acting directly on the cranial shape, rather than on size alone.
在个体发生的异速生长研究中，通常援引个体发生的尺度来解释亲缘关系密切的较小和较大形态之间的颅形态差异。这些形状的缩放变体被假设为常见生长异速生长的延伸或截断的结果。在这种情况下，大小的变化是决定因素，也许受到直接选择的影响，而颅形状的变化是副产品，本身不受直接选择的影响。然而，这些结论中的许多都是基于使用形状双变量概括的研究得出的。即使在生长异速生长的多元分析中，也存在关于灵长类动物中个体发生尺度的普遍性、共享轨迹需要达到的程度以及哪些分类群表现出缩放变体的属性的差异。在这项研究中，我们使用了一个大型的、比较性的个体发生样本、几何形态测量方法和多元统计检验来检查个体发生的异速生长，并评估大小在不同大小的亲缘关系密切的猫科动物的颅形态差异中是否主要是由大小的差异驱动的，也就是说，个体发生的尺度。然后，我们评估大小作为猫科动物颅部进化中最小进化阻力线的假说。我们发现，个体发生的异速生长模式在不同的分类群中有所不同，这表明严格意义上的个体发生尺度并不经常解释大多数形态差异，并且在进化枝内的大分类群和小分类群通常不是缩放变体。颅形状进化的各种个体发生途径的存在为直接作用于颅形状的选择提供了间接证据，而不仅仅是大小。
