Department of Biological Sciences, Florida Atlantic University, Boca Raton, FL 33431, USA
Apex Predators Program, National Marine Fisheries Service, Narragansett, RI 02882, USA.
J Exp Biol. 2018 Dec 12;221(Pt 24):jeb188318. doi: 10.1242/jeb.188318.
Cartilaginous shark skeletons experience axial deformation at the intervertebral joints, but also within the mineralized cartilaginous centrum, which can compress to between 3% and 8% of its original length in a free-swimming shark. Previous studies have focused on shark centra mechanical properties when loaded to failure; our goal was to determine properties when compressed to a biologically relevant strain. We selected vertebrae from six shark species and from the anterior and posterior regions of the vertebral column. Centra were X-radiographed to measure double cone proportion and apex angles, and were mechanically tested at three displacement rates to 4% strain. We determined the variation in toughness and stiffness of vertebral centra among shark species and ontogenetic stages, testing strain rates, and compared anterior and posterior regions of the vertebral column. Our results suggest that toughness and stiffness, which are positively correlated, may be operating in concert to support lateral body undulations, while providing efficient energy transmission and return in these swift-swimming apex predators. We analyzed the contribution of double cone proportion and apex angle to centra mechanical behavior. We found that the greatest stiffness and toughness were in the youngest sharks and from the posterior body, and there was significant interspecific variation. Significant inverse correlations were found between mechanical properties and double cone apex angle suggesting that properties can be partially attributed to the angle forming the double cone apex. These comparative data highlight the importance of understanding cartilaginous skeleton mechanics under a wide variety of loading conditions representative of swimming behaviors seen in the wild.
软骨鱼类的骨骼在椎间关节处发生轴向变形，但也在矿化软骨中心内发生变形，在自由游动的鲨鱼中，软骨中心可压缩至其原始长度的 3%至 8%。以前的研究集中在鲨鱼中心在失效时的机械性能；我们的目标是确定在压缩到生物相关应变时的性能。我们从六个鲨鱼物种以及脊柱的前区和后区选择了椎骨。对中心进行 X 射线照相以测量双锥体比例和顶点角度，并以三种位移率机械测试至 4%应变。我们确定了鲨鱼物种和个体发育阶段之间的椎骨中心韧性和刚度的变化，测试了应变率，并比较了脊柱的前区和后区。我们的结果表明，与韧性正相关的刚度可能协同作用以支持身体的侧向波动，同时为这些快速游动的顶级捕食者提供有效的能量传递和返回。我们分析了双锥体比例和顶点角度对中心机械行为的贡献。我们发现，最年轻的鲨鱼和身体后部的刚度和韧性最大，而且存在显著的种间差异。机械性能与双锥体顶点角度之间存在显著的负相关关系，这表明性能部分归因于形成双锥体顶点的角度。这些比较数据突出了在代表野生游泳行为的各种加载条件下理解软骨骨骼力学的重要性。
