Ivanović Ana, Arntzen Jan W
Faculty of Biology, University of Belgrade, Belgrade, Serbia.
Naturalis Biodiversity Center, Leiden, The Netherlands.
J Anat. 2018 Mar;232(3):359-370. doi: 10.1111/joa.12759. Epub 2017 Dec 14.
We carried out a comparative morphometric analysis of 56 species of salamandrid salamanders, representing 19 out of 21 extant genera, with the aim of uncovering the major patterns of skull shape diversification, and revealing possible trends and directions of evolutionary change. To do this we used micro-computed tomography scanning and three-dimensional geometric morphometrics, along with a well-resolved molecular phylogeny. We found that allometry explains a relatively small amount of shape variation across taxa. Congeneric species of salamandrid salamanders are more similar to each other and cluster together producing distinct groups in morphospace. We detected a strong phylogenetic signal and little homoplasy. The most pronounced changes in the skull shape are related to the changes of the frontosquamosal arch, a unique feature of the cranial skeleton for the family Salamandridae, which is formed by processes arising from the frontal and squamosal bones that arch over the orbits. By mapping character states over the phylogeny, we found that a reduction of the frontosquamosal arch occurs independently in three lineages of the subfamily Pleurodelinae. This reduction can probably be attributed to changes in the development and ossification rates of the frontosquamosal arch. In general, our results are similar to those obtained for caecilian amphibians, with an early expansion into the available morphospace and a complex history characterizing evolution of skull shape in both groups. To evaluate the specificity of the inferred evolutionary trajectories and Caudata-wide trends in the diversity of skull morphology, information from additional groups of tailed amphibians is needed.
我们对56种蝾螈科蝾螈进行了比较形态测量分析，这些蝾螈代表了21个现存属中的19个，目的是揭示头骨形状多样化的主要模式，并揭示进化变化的可能趋势和方向。为此，我们使用了微计算机断层扫描和三维几何形态测量学，以及一个解析度良好的分子系统发育树。我们发现，异速生长在不同分类单元中解释的形状变化相对较少。蝾螈科蝾螈的同属物种彼此更相似，并聚集在一起，在形态空间中形成不同的组。我们检测到强烈的系统发育信号，且几乎没有同形现象。头骨形状最明显的变化与额鳞弓的变化有关，额鳞弓是蝾螈科颅骨骨骼的一个独特特征，它由额骨和鳞骨产生的突起形成，这些突起在眼眶上方呈拱形。通过在系统发育树上绘制特征状态，我们发现额鳞弓的缩小在无肺螈亚科的三个谱系中独立发生。这种缩小可能归因于额鳞弓发育和骨化速率的变化。总体而言，我们的结果与蚓螈两栖动物的结果相似，两者都早期扩展到可用的形态空间，并且头骨形状进化具有复杂的历史。为了评估推断的进化轨迹的特异性以及尾两栖动物头骨形态多样性的全尾目趋势，还需要来自其他有尾两栖动物群体的信息。
