CIBIO, Centro de Investigação em Biodiversidade e Recursos Genéticos, Vairão, Portugal.
J Anat. 2012 May;220(5):423-34. doi: 10.1111/j.1469-7580.2012.01485.x. Epub 2012 Feb 23.
Scorpions depend on their pedipalps for prey capture, defense, mating and sensing their environment. Some species additionally use their pedipalps for burrowing or climbing. Because the pincers or chelae at the end of the pedipalps vary widely in shape, they have been used as part of a suite of characters to delimit ecomorphotypes. We here evaluate the influence of the different chela cuticular shapes on their performance under natural loading conditions. Chelae of 20 species, representing seven families and spanning most of the range of chela morphologies, were assigned to clusters based on chela shape parameters using hierarchical cluster analysis. Several clusters were identified corresponding approximately to described scorpion ecomorphotypes. Finite element models of the chela cuticulae were constructed from CT scans and loaded with estimated pinch forces based on in vivo force measurements. Chela shape clusters differed significantly in mean Von Mises stress and strain energy. Normalized FEA showed that chela shape significantly influenced Von Mises stress and strain energy in the chela cuticula, with Von Mises stress varying up to an order of magnitude and strain energy up to two orders of magnitude. More elongate, high-aspect ratio chela forms showed significantly higher mean stress compared with more robust low-aspect ratio forms. This suggests that elongate chelae are at a higher risk of failure when operating near the maximum pinch force. Phylogenetic independent contrasts (PIC) were calculated based on a partly resolved phylogram with branch lengths based on an alignment of the 12S, 16S and CO1 mitochondrial genes. PIC showed that cuticular stress and strain in the chela were correlated with several shape parameters, such as aspect ratio, movable finger length, and chela height, independently of phylogenetic history. Our results indicate that slender chela morphologies may be less suitable for high-force functions such as burrowing and defense. Further implications of these findings for the ecology and evolution of the different chela morphologies are discussed.
蝎子依靠其步足捕食、防御、交配和感知环境。一些物种还会利用步足挖掘或攀爬。由于步足末端的钳子或螯的形状差异很大，因此它们被用作区分生态型的特征之一。我们在这里评估不同的螯肢表皮形状对其在自然加载条件下的性能的影响。使用层次聚类分析，根据螯肢形状参数将 20 个代表 7 个科且涵盖了大多数螯肢形态范围的物种的螯肢分配到聚类中。根据描述的蝎子生态型，确定了几个集群。使用 CT 扫描构建了螯肢表皮的有限元模型，并根据体内力测量估计的夹力对其进行了加载。螯肢形状聚类在平均 Von Mises 应力和应变能方面存在显著差异。归一化 FEA 表明，螯肢形状显著影响了螯肢表皮中的 Von Mises 应力和应变能，Von Mises 应力变化高达一个数量级，应变能变化高达两个数量级。与更粗壮的低纵横比形式相比，更长、高纵横比的螯肢形式表现出明显更高的平均应力。这表明，当操作接近最大夹力时，细长的螯肢更容易失效。根据基于 12S、16S 和 CO1 线粒体基因的部分解析系统发育树和分支长度计算了系统发育独立对比（PIC）。PIC 表明，螯肢的表皮应力和应变与几个形状参数相关，例如纵横比、可动指长度和螯肢高度，与系统发育历史无关。我们的研究结果表明，细长的螯肢形态可能不太适合高力功能，例如挖掘和防御。进一步讨论了这些发现对不同螯肢形态的生态学和进化的影响。
