Function and Evolution of Jaw-Muscle Fiber Type in Primates

研究肌肉可以帮助我们了解早期人类和其他灭绝的灵长类动物的饮食。颌肌纤维类型在微调颌部肌肉以完成特定的运动任务方面发挥着重要作用，例如咀嚼和有力的咬合。这项研究将研究一系列灵长类动物的颌部肌肉纤维类型，并使用这些数据来检验关于灵长类动物颌部肌肉模式进化的三个假说。这项工作的结果将通过以下方式为肌肉和饮食之间的关系提供新的见解：i)增加关于形成摄食系统解剖的行为和生态因素的知识；ii)增进我们对颌肌纤维类型和整个肌肉解剖如何共同作用以产生进食和攻击性咬合所需的颌部运动和颌力的理解；以及(Iii)完善活的和化石的灵长类动物的咀嚼生物力学模型。这项工作的一个核心组成部分包括对本科生、研究生和博士后学者，包括妇女和代表性不足的少数民族，进行最先进的肌肉纤维分型方法的培训和指导。此外，成果还将纳入旨在让小学女孩接触科学的社区外展计划。最后，这个项目将产生一个独特的肌肉组织数字图像和幻灯片集合，供科学界用于教学和研究。闭口肌是咀嚼系统的马达。总的来说，这些肌肉负责产生与进食行为以及非进食口腔行为相关的下巴运动和力，如攻击性咬人和张开大嘴以显示狗的威胁。虽然纤维结构是整个肌肉功能的重要决定因素，但在缺乏有关纤维类型的信息的情况下，其功能和适应性的重要性不能得到充分的认识。缺乏灵长类纤维表型的数据限制了1)关于颌肌纤维表型变异的认识；2)这种变异对行为和表现的功能意义；以及3)我们可以在活的和化石物种中模拟和检验摄食系统功能和表现假说的特异性。为了提供一个更完整的框架，将灵长类咀嚼解剖学和生理学的测量与功能和性能联系起来，研究人员将收集和分析关于颌肌纤维类型组成和分布的新数据，这些数据来自于在关键的摄食或咬人行为上存在分歧的选定的密切相关的链状灵长类和类人灵长类动物。收集的数据将用于：(I)使用最先进的免疫组织化学技术来量化灵长类闭口肌中肌球蛋白重链(MHC)纤维的类型组成和分布；(Ii)测试三种关键的功能和适应性假说，这些假说已经被提出来解释哺乳动物颌肌中纤维表型的演变：频繁招募假说、攻击性咬合假说和高咬合力假说；以及(Iii)评估纤维表型、纤维结构和杠杆之间的对应关系，以完善咀嚼生物力学的模型。该项目将提供有关灵长类闭口肌中发现的收缩蛋白的新数据，促进对驱动灵长类颌部肌肉纤维表型变化的生态和行为因素的了解，并对摄食系统形态的关键组成部分，如纤维结构、纤维表型和杠杆如何结合以促进或限制灵长类动物的摄食行为产生新的见解，包括作为解释早期人类祖先摄食行为和饮食的模型的物种。

Studying muscle can help us to understand the diets of early humans and other extinct primates. Jaw-muscle fiber types play an important role in fine-tuning the jaw muscles for specific motor tasks such as chewing and powerful biting. This research will study jaw-muscle fiber types across a range of primate species and use those data to test three hypotheses about the evolution of jaw muscle patterns in primates. Results of this work will provide new insights into the relationship between muscle and diet by i) increasing knowledge about the behavioral and ecological factors that shape feeding-system anatomy; ii) advancing our understanding of how jaw-muscle fiber types and whole muscle anatomy work together to generate the jaw movements and jaw forces necessary during feeding and aggressive biting; and (iii) refining models of chewing biomechanics in living and fossil primates. A central component of this work includes the training and mentoring of undergraduate and graduate students and postdoctoral scholars, including women and underrepresented minorities, in state-of-the-art methods for muscle fiber typing. In addition, results will be incorporated in community outreach programs aimed at exposing primary school girls to science. Lastly, this project will generate a unique collection of digital images and slides of muscle tissue that will be made available to the scientific community for teaching and research.The jaw-closing muscles are the motors of the masticatory system. Collectively, these muscles are responsible for generating the jaw movements and forces associated with feeding behaviors as well as non-feeding oral behaviors such as aggressive biting and wide-mouth opening for canine threat display. While fiber architecture is an important determinant of whole muscle function, its functional and adaptive significance cannot be fully appreciated in the absence of information on fiber type. This lack of data on primate fiber phenotype limits 1) knowledge about variation in jaw-muscle fiber phenotype; 2) the functional significance of this variation for behavior and performance; and 3) the specificity with which we can model and test hypotheses of feeding-system function and performance in both living and fossil species. To provide a more complete framework for linking measures of primate masticatory anatomy and physiology with function and performance, the investigators will collect and analyze novel data on jaw-muscle fiber type composition and distribution in select, closely related species of strepsirrhine and anthropoid primates that diverge in a key feeding or biting behavior. The data collected will be used to: (i) quantify the myosin heavy chain (MHC) fiber type composition and distribution in primate jaw-closing muscles using state-of-the-art immunohistochemistry; (ii) test three key functional and adaptive hypotheses that have been advanced to explain the evolution of fiber phenotype in mammalian jaw muscles: the frequent recruitment hypothesis, the aggressive bite hypothesis, and the high occlusal force hypothesis; and (iii) assess the correspondence among fiber phenotype, fiber architecture and leverage with the goal of refining models of masticatory biomechanics. This project will provide novel data on the contractile proteins found in primate jaw-closing muscles, advance knowledge of the ecological and behavioral factors that drove changes in the primate jaw-muscle fiber phenotype, and yield new insights into how key components of feeding-system morphology such as fiber architecture, fiber phenotype and leverage combine to facilitate or constrain feeding behavior in primates, including species that have been advanced as models for interpreting feeding behavior and diet in early human ancestors.