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Comparative anatomy of the middle ear in some lizard species with comments on the evolutionary changes within Squamata
PeerJ ( IF 2.7 ) Pub Date : 2021-07-22 , DOI: 10.7717/peerj.11722
Paola María Sánchez-Martínez 1 , Juan D Daza 2 , Julio Mario Hoyos 1, 3
Affiliation  

The skeleton of the middle ear of lizards is composed of three anatomical elements: columella, extracolumella, and tympanic membrane, with some exceptions that show modifications of this anatomy. The main function of the middle ear is transforming sound waves into vibrations and transmitting these to the inner ear. Most middle ear studies mainly focus on its functional aspects, while few describe the anatomy in detail. In lizards, the morphology of the columella is highly conservative, while the extracolumella shows variation in its presence/absence, size, and the number of processes present on the structure. In this work, we used diaphanized and double-stained specimens of 38 species of lizards belonging to 24 genera to study the middle ear’s morphology in a comparative framework. Results presented here indicate more variation in the morphology of the extracolumella than previously known. This variation in the extracolumella is found mainly in the pars superior and anterior processes, while the pars inferior and the posterior process are more constant in morphology. We also provide new information about the shape of gekkotan extracolumella, including traits that are diagnostic for the iguanid and gekkonid middle ear types. The data collected in this study were combined with information from published descriptive works. The new data included here refers to the length of the columella relative to the extracolumella central axis length, the general structure of the extracolumella, and the presence of the internal process. These characters were included in ancestral reconstruction analysis using Bayesian and parsimony approaches. The results indicate high levels of homoplasy in the variation of the columella-extracolumella ratio, providing a better understanding of the ratio variation among lizards. Additionally, the presence of four processes in the extracolumella is the ancestral state for Gekkota, Pleurodonta, and Xantusiidae, and the absence of the internal processes is the ancestral state for Gekkota, Gymnophthalmidae, and Scincidae; despite the fact that these groups convergently develop these character states, they could be used in combination with other characters to diagnose these clades. The posterior extension in the pars superior and an anterior process with some small and sharp projections is also a diagnostic trait for Gekkota. A more accurate description of each process of the extracolumella and its variation needs to be evaluated in a comprehensive analysis, including a greater number of species. Although the number of taxa sampled in this study is small considering the vast diversity of lizards, the results provide an overall idea of the amount of variation of the middle ear while helping to infer the evolutionary history of the lizard middle ear.

中文翻译:

一些蜥蜴物种中耳的比较解剖学以及对有鳞蜥蜴进化变化的评论

蜥蜴中耳的骨骼由三个解剖元件组成:小柱、小柱外和鼓膜,但有一些例外情况显示了这种解剖结构的修改。中耳的主要功能是将声波转化为振动并将其传递到内耳。大多数中耳研究主要集中在其功能方面,而很少详细描述解剖结构。在蜥蜴中,小柱的形态是高度保守的,而小柱外的存在/不存在、大小和结构上存在的突起数量显示出变化。在这项工作中,我们使用属于 24 属的 38 种蜥蜴的透明化和双染色标本在比较框架中研究中耳的形态。此处显示的结果表明,小柱外形态的变化比以前已知的要多。小柱外的这种变异主要见于上突和前突,而下突和后突在形态上更为恒定。我们还提供了有关壁虎科动物小柱形状的新信息,包括对鬣蜥和壁虎中耳类型具有诊断意义的特征。本研究中收集的数据与已发表的描述性作品的信息相结合。这里包含的新数据是指小柱相对于小柱外中心轴长度的长度、小柱外的一般结构以及内部突起的存在。这些特征被包括在使用贝叶斯和简约方法的祖先重建分析中。结果表明,小柱-小柱外比值的变化具有高水平的同质性,从而可以更好地了解蜥蜴之间的比值变化。此外,外小管内四个突起的存在是壁虎、侧齿兽和黄蜂科的祖先状态,而内部突起的缺失则是壁虎、裸眼虫科和鼠尾藻的祖先状态;尽管这些群体会集中发展这些特征状态,但它们可以与其他特征结合使用来诊断这些进化枝。上肢的后伸和带有一些小而尖锐的突起的前突也是 Gekkota 的诊断特征。需要在综合分析中对小柱外的每个过程及其变异进行更准确的描述,包括更多的物种。尽管考虑到蜥蜴的巨大多样性,本研究中采样的分类群数量很少,但结果提供了中耳变异量的整体概念,同时有助于推断蜥蜴中耳的进化历史。
更新日期:2021-07-22
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