Department of Evolutionary Biology, Institute for Biological Research "Siniša Stanković", National Institute of the Republic of Serbia, University of Belgrade, Belgrade, Serbia.
J Anat. 2024 Jul;245(1):97-108. doi: 10.1111/joa.14030. Epub 2024 Mar 2.
The modular organization of tetrapod paired limbs and girdles, influenced by the expression of Hox genes is one of the primary driving forces of the evolution of animal locomotion. The increased morphological diversification of the paired limbs is correlated with reduced between-limb covariation, while correlation within the elements is usually higher than between the elements. The tailed amphibians, such as Lissotriton newts, have a biphasic lifestyle with aquatic and terrestrial environments imposing different constraints on limb skeleton. By employing the methods of computerized microtomography and 3D geometric morphometrics, we explored the pattern of morphological variation, disparity, modularity and morphological integration in the proximal parts of the anterior limbs of six species of Eurasian small bodied newts. Although the species significantly differ in limb shape, there is a great overlap in morphology of scapula and humerus, and there are no differences in morphological disparity. For the scapula, the shape differences related to the duration of the aquatic period are in length, depth and curvature. The shape of the humerus is not affected by the length of aquatic period, and shape differences between the species are related to robustness of the body. The length of aquatic period has statistically supported phylogenetic signal. The scapula and humerus are structures of varying modularity. For the humerus, the strongest support on the phylogenetic level was for the capitulum/shaft hypothesis, which can also be interpreted as functional modularity. For the scapula, the greatest support was for the antero-posterior hypothesis of modularity in case of Lissotriton vulgaris, which can be explained by different functional roles and muscle insertion patterns, while there was no phylogenetic modularity. The modularity patterns seem to correspond with the general tetrapod pattern, with modularity being more pronounced in the distal structure. The future research should include more salamandrid taxa with different habitat preferences and both adult and larval stages, in order to explore how size, phylogeny and ecology affect the morphology and covariation patterns of limbs.
四足动物成对附肢和腰带的模块化组织受 Hox 基因表达的影响，是动物运动进化的主要驱动力之一。成对附肢形态多样性的增加与附肢之间的协变减少相关，而元素内部的相关性通常高于元素之间的相关性。有尾两栖动物，如蝾螈，具有水生和陆生环境的双相生活方式，这对附肢骨骼施加了不同的限制。通过采用计算机微断层扫描和 3D 几何形态测量学方法，我们研究了欧亚大陆小体型蝾螈的六种前肢近端部分的形态变异、离散度、模块性和形态整合模式。尽管这些物种在肢体形状上有显著差异，但肩胛骨和肱骨的形态有很大的重叠，形态离散度没有差异。对于肩胛骨，与水生期持续时间相关的形状差异在于长度、深度和曲率。肱骨的形状不受水生期长度的影响，物种之间的形状差异与身体的健壮程度有关。水生期的长度在统计学上具有支持进化的信号。肩胛骨和肱骨的结构具有不同的模块性。对于肱骨，在进化水平上最强的支持是头状骨/轴假说，也可以解释为功能模块性。对于肩胛骨，在 Lissotriton vulgaris 中，对前后假说的支持最大，这可以用不同的功能作用和肌肉插入模式来解释，而没有进化模块性。模块化模式似乎与一般四足动物的模式相对应，在远端结构中模块性更为明显。未来的研究应包括具有不同生境偏好的更多蝾螈类群以及成年和幼虫阶段，以探讨大小、进化和生态如何影响四肢的形态和协变模式。
