Bishop Peter J, Wright Mark A, Pierce Stephanie E
Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology,Harvard University, Cambridge, Massachusetts, United States of America.
Geosciences Program, Queensland Museum, Brisbane, Queensland, Australia.
PeerJ. 2021 Nov 29;9:e12574. doi: 10.7717/peerj.12574. eCollection 2021.
Skeletal muscle mass, architecture and force-generating capacity are well known to scale with body size in animals, both throughout ontogeny and across species. Investigations of limb muscle scaling in terrestrial amniotes typically focus on individual muscles within select clades, but here this question was examined at the level of the whole limb across amniotes generally. In particular, the present study explored how muscle mass, force-generating capacity (measured by physiological cross-sectional area) and internal architecture (fascicle length) scales in the fore- and hindlimbs of extant mammals, non-avian saurians ('reptiles') and bipeds (birds and humans). Sixty species spanning almost five orders of magnitude in body mass were investigated, comprising previously published architectural data and new data obtained dissections of the opossum and the tegu lizard . Phylogenetic generalized least squares was used to determine allometric scaling slopes (exponents) and intercepts, to assess whether patterns previously reported for individual muscles or functional groups were retained at the level of the whole limb, and to test whether mammals, reptiles and bipeds followed different allometric trajectories. In general, patterns of scaling observed in individual muscles were also observed in the whole limb. Reptiles generally have proportionately lower muscle mass and force-generating capacity compared to mammals, especially at larger body size, and bipeds exhibit strong to extreme positive allometry in the distal hindlimb. Remarkably, when muscle mass was accounted for in analyses of muscle force-generating capacity, reptiles, mammals and bipeds almost ubiquitously followed a single common scaling pattern, implying that differences in whole-limb force-generating capacity are principally driven by differences in muscle mass, not internal architecture. In addition to providing a novel perspective on skeletal muscle allometry in animals, the new dataset assembled was used to generate pan-amniote statistical relationships that can be used to predict muscle mass or force-generating capacity in extinct amniotes, helping to inform future reconstructions of musculoskeletal function in the fossil record.
众所周知，在动物个体发育过程以及跨物种比较中，骨骼肌质量、结构和产生力量的能力都与体型大小相关。对陆生羊膜动物肢体肌肉缩放比例的研究通常聚焦于特定类群中的单个肌肉，但在此研究中，该问题是在整个羊膜动物肢体层面进行考察的。具体而言，本研究探讨了现存哺乳动物、非鸟类蜥蜴（“爬行动物”）和两足动物（鸟类和人类）的前肢和后肢中肌肉质量、产生力量的能力（通过生理横截面积测量）以及内部结构（肌束长度）是如何缩放的。研究调查了体重跨度近五个数量级的60个物种，包括先前已发表的结构数据以及通过对负鼠和鬃狮蜥进行解剖获得的新数据。采用系统发育广义最小二乘法来确定异速生长缩放斜率（指数）和截距，以评估先前针对单个肌肉或功能组所报道的模式在整个肢体层面是否得以保留，并检验哺乳动物、爬行动物和两足动物是否遵循不同的异速生长轨迹。总体而言，在单个肌肉中观察到的缩放模式在整个肢体中也能观察到。与哺乳动物相比，爬行动物通常肌肉质量和产生力量的能力比例较低，尤其是在体型较大时，而两足动物在后肢远端表现出强烈至极强烈的正异速生长。值得注意的是，在对肌肉产生力量的能力进行分析时，如果考虑到肌肉质量，爬行动物、哺乳动物和两足动物几乎普遍遵循单一的共同缩放模式，这意味着整个肢体产生力量能力的差异主要由肌肉质量的差异驱动，而非内部结构。除了为动物骨骼肌异速生长提供新视角外，所收集的新数据集还用于生成泛羊膜动物统计关系，可用于预测已灭绝羊膜动物的肌肉质量或产生力量的能力，有助于为未来化石记录中肌肉骨骼功能的重建提供参考。
