Doctoral Dissertation Research: The Biomechanics of Vertical Clinging and Grasping in Primates

杜克大学的博士生劳拉·约翰逊（Laura Johnson）将在丹尼尔·施密特博士的指导下，对灵长类动物一组特定姿势的生物力学进行研究——这些姿势是直立地依附在树干上时所采取的。这项研究的重点是与灵长类动物进化起源相关的一个关键适应性转变，即“入侵”复杂的树木环境。早期灵长类动物进化出了用指甲抓握的手和脚，而不是像其他树栖物种（如松鼠）那样保留爪子。这种失去爪子的进化事件给生物力学家提出了一个关键的悖论，即理解树栖灵长类动物如何在没有爪子的情况下有效地抓住巨大的垂直树干。这个问题的调查解决了现存和祖先灵长类动物对树栖生态位的形态适应。由于在树栖环境中无法利用爪子，灵长类动物必须用尽量减少肌肉活动的姿势抓住树木。先前对哺乳动物生物力学的研究表明，在涉及不同肌肉骨骼解剖结构、基质尺寸和体重的三种情况下，存在假设的变异。为了检验这些变量，研究人员在实验室环境中观察了来自杜克狐猴中心的8种灵长类动物的样本，这些物种在解剖结构和体重上都有所不同。个体被提示垂直地依附和抓住四种尺寸相对于他们的体重增加的基质。地松鼠，卡罗来尼松鼠，被列为有爪的非灵长类哺乳动物外群。视频数据是通过一个八摄像头系统收集的，以记录三维的姿势，而单肢加载模式的数据是通过插入基板的力板收集的。这项研究的结果将揭示导致灵长类动物失去爪子而选择指甲的进化压力，这种适应可能与灵长类动物身体大小的增加有关，并且是人类手部抓取的必要先驱。该项目还包括本科生培训和向其他研究人员和公众（包括当地K-12学校）广泛传播数据，并将在动物园设计和灵长类动物保护中得到应用。

Doctoral student Laura Johnson (Duke University), under the supervision of Dr. Daniel Schmitt, will investigate the biomechanics of a specific set of primate postures - those adopted while vertically clinging to tree trunks. The research focuses on a key adaptive shift associated with the evolutionary origins of primates, that of the 'invasion' of the complex arboreal environment. Early primates evolved grasping hands and feet with nails, rather than keeping claws, such as found in other tree-dwelling species (e.g., squirrels). This evolutionary event of loss of claws raises a critical paradox for biomechanists, that of understanding how arboreal primates maintain an effective grip on large, vertical tree trunks without claws. The investigation of this question addresses morphological adaptation to an arboreal niche in both living and ancestral primates. Not being able to take advantage of claws in the arboreal habitat, primates must hold onto the trees by using postures that will minimize muscular work. Prior research on mammalian biomechanics suggests hypothesized variation within three contexts involving differing musculoskeletal anatomies, substrate sizes, and body weights. To examine these variables, a sample of eight primate species from the Duke Lemur Center which differ in anatomies and body weights are observed in a laboratory setting. Individuals are prompted to vertically cling and grasp to substrates of four increasing sizes, relative to their body weight. The ground squirrel, Scurius caroliniensis, is included as a clawed non-primate mammalian outgroup. Video data are collected using an eight-camera system to document postures in three dimensions, and data on single-limb loading patterns are collected utilizing force plates inserted into the substrate.Results from this study will shed light on the evolutionary pressures that led primates to lose claws in favor of nails, an adaptation that may be related to primate body size increase, and is a necessary precursor to human hand grasping. The project also incorporates undergraduate training and broad dissemination of data to other researchers and the public, including local K-12 schools, and will find application in zoo design and primate conservation.