Monitoring muscle over three orders of magnitude: Widespread positive allometry among locomotor and body support musculature in the pectoral girdle of varanid lizards (Varanidae)
Monitoring muscle over three orders of magnitude: Widespread positive allometry among locomotor and body support musculature in the pectoral girdle of varanid lizards (Varanidae)
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DOI：
10.1111/joa.13273
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发表时间：
2020-07-24
影响因子：
2.4
通讯作者：
Clemente, Christofer J.
中科院分区：
文献类型：
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作者：
Cieri, Robert L.;Dick, Taylor J. M.;Clemente, Christofer J.
骨骼肌的设计存在功能权衡。肌肉力量取决于平行肌纤维的数量，而缩短速度和操作距离取决于肌束长度，导致肌肉可以产生的最大力量与其快速改变长度和收缩的能力之间的权衡。随着动物体型的增大，这种权衡变得更加明显，因为肌肉力量与面积（长度（2））成比例，而体重与体积（长度（3））成比例。为了了解这种肌肉权衡以及动物如何应对体型大小带来的生物力学后果，我们研究了蜥蜴胸带的肌肉特性。蜥蜴是研究肌肉特性缩放的理想群体，因为它们在体重的五个数量级上保持相似的身体比例和姿势，并且是高度活跃、适应陆地的爬行动物。我们测量了 8 个物种的 13 个人的 27 块胸带肌肉的肌肉质量、生理横截面积、肌束长度、近端和远端肌腱长度以及近端和远端力臂，重量从 64 克到 40 公斤不等。使用标准和系统发育学简化的长轴回归来研究肌肉结构特性如何随体型变化。肌肉质量（标度指数 >1）、生理横截面积（标度指数 >0.66）普遍存在异速生长，但肌腱长度则不然（标度指数 >0.33）。肌肉质量的正异速生长在负责躯干向前平移和弯曲肘部的肌肉中普遍存在，并且在肱骨量角肌和腕屈肌中几乎普遍存在。 PCSA 的正异速生长在躯干平移者和肱骨量角者中也很常见，尽管不如肌肉质量。肌束长度的正缩放并不普遍，但在肱骨量角器中很常见。与我们之前的研究显示的骨盆带相比，正异速生长的胸带肌肉比例更高，这表明巨蜥的质心可能随着体型的大小而向颅骨移动，或者胸带可能在较大物种的运动中发挥更主导的作用。主要与推进或双重作用相关的肌肉生理横截面积的缩放指数通常高于主要与对抗重力的支撑相关的指数，这表明运动需求对肌肉结构的影响至少与身体支撑具有相同的影响。总体而言，这些结果表明，较大的蜥蜴通过发育具有较高生理横截面积的较大胸肌来补偿较高体型下运动和身体支撑增加的生物力学需求。运动导向的胸带肌中束长度的等距缩放率表明，较大的蜥蜴可能被迫使用较短的步幅长度，但这个问题可以通过滑动喙骨关节提供的肢体偏移的增加来避免。
There is a functional trade-off in the design of skeletal muscle. Muscle strength depends on the number of muscle fibers in parallel, while shortening velocity and operational distance depend on fascicle length, leading to a trade-off between the maximum force a muscle can produce and its ability to change length and contract rapidly. This trade-off becomes even more pronounced as animals increase in size because muscle strength scales with area (length(2)) while body mass scales with volume (length(3)). In order to understand this muscle trade-off and how animals deal with the biomechanical consequences of size, we investigated muscle properties in the pectoral girdle of varanid lizards. Varanids are an ideal group to study the scaling of muscle properties because they retain similar body proportions and posture across five orders of magnitude in body mass and are highly active, terrestrially adapted reptiles. We measured muscle mass, physiological cross-sectional area, fascicle length, proximal and distal tendon lengths, and proximal and distal moment arms for 27 pectoral girdle muscles in 13 individuals across 8 species ranging from 64 g to 40 kg. Standard and phylogenetically informed reduced major axis regression was used to investigate how muscle architecture properties scale with body size. Allometric growth was widespread for muscle mass (scaling exponent >1), physiological cross-sectional area (scaling exponent >0.66), but not tendon length (scaling exponent >0.33). Positive allometry for muscle mass was universal among muscles responsible for translating the trunk forward and flexing the elbow, and nearly universal among humeral protractors and wrist flexors. Positive allometry for PCSA was also common among trunk translators and humeral protractors, though less so than muscle mass. Positive scaling for fascicle length was not widespread, but common among humeral protractors. A higher proportion of pectoral girdle muscles scaled with positive allometry than our previous work showed for the pelvic girdle, suggesting that the center of mass may move cranially with body size in varanids, or that the pectoral girdle may assume a more dominant role in locomotion in larger species. Scaling exponents for physiological cross-sectional area among muscles primarily associated with propulsion or with a dual role were generally higher than those associated primarily with support against gravity, suggesting that locomotor demands have at least an equal influence on muscle architecture as body support. Overall, these results suggest that larger varanids compensate for the increased biomechanical demands of locomotion and body support at higher body sizes by developing larger pectoral muscles with higher physiological cross-sectional areas. The isometric scaling rates for fascicle length among locomotion-oriented pectoral girdle muscles suggest that larger varanids may be forced to use shorter stride lengths, but this problem may be circumvented by increases in limb excursion afforded by the sliding coracosternal joint.