Diversity of Limb-Bone Safety Factors for Locomotion in Terrestrial Vertebrates: Evolution and Mixed Chains
Diversity of Limb-Bone Safety Factors for Locomotion in Terrestrial Vertebrates: Evolution and Mixed Chains
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DOI：
10.1093/icb/icu032
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发表时间：
2014-12-01
影响因子：
2.6
通讯作者：
Sheffield, K. Megan
中科院分区：
文献类型：
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作者：
Blob, Richard W.;Espinoza, Nora R.;Sheffield, K. Megan
在陆地上运动时，脊椎动物的四肢骨骼暴露在负荷下。像大多数生物结构一样，四肢骨骼具有承受比通常经历的更大载荷的能力，称为安全系数（SF）。肢骨SFs的多样性有多大？哪些因素与这种变化相关？我们从两个角度研究了这些问题。首先，我们评估了不同谱系的股骨运动SF，包括蝾螈，青蛙，海龟，蜥蜴，鳄鱼，和有袋动物（负鼠）。与值的后肢元素在运行的鸟类和真兽目哺乳动物的比较表明四肢骨SF的系统发育多样性。高SF（类似于7）对于四足动物来说是原始的，但低负荷和骨骼强度的提高在不同的谱系中有不同程度的贡献;此外，鸟类和真兽目似乎独立地进化出了较低的SF。其次，我们测试的假设，SF将是相似的四肢骨骼内的一个分类单元，通过比较数据从短吻鳄的肱骨和股骨。无论是在弯曲和扭转，我们发现一个较高的SF为肱骨比股骨。如果骨骼具有不同的负荷变化、不同的维护成本或通常的高SF值，则已经预测了跨元素的不同SF的这种“混合链”。尽管肱骨和股骨的载荷变化相似，但对于肱骨来说，高SF可能成本较低，因为它比股骨小。短吻鳄的高SF也可能促进它们四肢骨骼之间SF的差异。然而，除了这些具体的发现，我们的研究结果更普遍的含义是，肢体骨SFs的多样性的评估可以提供重要的视角，以指导未来的研究。特别是，更完整的了解SF的变化可以提供深入了解的因素，促进了进化辐射的陆地运动功能的脊椎动物。
During locomotion over land, vertebrates' limb bones are exposed to loads. Like most biological structures, limb bones have a capacity to withstand greater loads than they usually experience, termed a safety factor (SF). How diverse are limb-bone SFs, and what factors correlate with such variation? We have examined these questions from two perspectives. First, we evaluated locomotor SF for the femur in diverse lineages, including salamanders, frogs, turtles, lizards, crocodilians, and marsupials (opossums). Comparisons with values for hind-limb elements in running birds and eutherian mammals indicate phylogenetic diversity in limb-bone SF. A high SF (similar to 7) is primitive for tetrapods, but low magnitudes of load and elevated strength of bones contribute to different degrees across lineages; moreover, birds and eutherians appear to have evolved lower SFs independently. Second, we tested the hypothesis that SFs would be similar across limb bones within a taxon by comparing data from the humerus and femur of alligators. Both in bending and in torsion, we found a higher SF for the humerus than for the femur. Such a "mixed chain'' of different SFs across elements has been predicted if bones have differing variabilities in load, different costs to maintain, or high SF values in general. Although variability in load is similar for the humerus and femur, a high SF may be less costly for the humerus because it is smaller than the femur. The high SFs of alligators also might facilitate differences in SF among their limb bones. Beyond these specific findings, however, a more general implication of our results is that evaluations of the diversity of limb-bone SFs can provide important perspective to direct future research. In particular, more complete understanding of variation in SF could provide insight into factors that promoted the evolutionary radiation of terrestrial locomotor function in vertebrates.