Doctoral Dissertation Improvement: Ontogenetic development of postcranial adaptations to bipedalism in the rat

人类两足动物的进化标志着我们血统的起源，并代表着运动模式和肌肉骨骼形态的重大转变。然而，支撑这种运动变化的进化机制尚不清楚，相互竞争的模型表明，不同的选择压力是导致两足动物特征产生的原因。亚利桑那大学博士生亚当·福斯特在大卫·雷希伦博士的指导下进行的研究，将确定形态如何响应行为的模式，有助于我们理解两足动物的进化。这项研究直接测试了机械载荷的大小和方向(从四足动物到两足动物站立和运动的转变)在个体发育和成年期间后颅骨中产生适应性形态方面所起的作用。这项研究探索了三个主要问题：(1)两足站立和/或两足行走在骨骼形态的适应性变化中具有什么作用，(2)个体发育(即发育可塑性)在适应性两足动物形态生成中的作用是什么，以及(3)在个体发育过程中与运动变化相关的形态变化是否影响运动学和能量学？老鼠将被放置在跑步机上的定制马具系统中，当皮带不运动时，该系统允许舒适的两足运动或静态负荷，并将每周5天，每天锻炼或站立一小时，持续90天。骨骼变化通过微型CT扫描进行跟踪，运动学和能量学数据检查与形态变化相关的潜在能源成本降低。这些发现将有助于确定行为是如何驱动形态适应的，以及哪些形态可能是最早的原始人随着运动方式的变化而进化的。这项研究通过直接让本科生参与数据收集和分析来增加他们的研究机会，并涉及到与社区的接触。这项研究的结果将用于在当地一所高中开发一个进化实验室；该实验室和扫描结果将成为学生的永久资源。

The evolution of bipedalism in hominins marks the origins of our lineage and represents a significant shift in locomotor pattern and musculoskeletal morphology. The evolutionary mechanisms that underpin this locomotor shift are unclear, however, with competing models suggesting differing selective pressures were responsible for the generation of bipedal traits. Research by doctoral student Adam Foster (University of Arizona), under the supervision of Dr. David Raichlen, will identify patterns in how morphology responds to behavior, contributing to our understanding of bipedal evolution. The study directly tests for the roles that the amount and direction of mechanical loads (a shift from quadrupedal to bipedal standing and locomotion) have in generating adaptive morphology in the postcranial skeleton during ontogeny and adulthood, using a rat model. The research explores three main questions: (1) what role do bipedal standing and/or bipedal walking have in generating adaptive changes in skeletal morphology, (2) what is the role of ontogeny (i.e., developmental plasticity) in the generation of adaptive bipedal morphology, and (3) do morphological changes associated with locomotor shifts during ontogeny impact kinematics and energetics? Rats will be placed in a custom harness system mounted over a treadmill that allows for comfortable bipedal locomotion or static loading when the belt is not in motion, and will exercise or stand for one hour a day, 5 days a week, for 90 days. Skeletal changes are tracked through micro-CT scans, and kinematics and energetics data examine potential energy cost reductions associated with morphological changes. The findings will contribute to identifying how behavior drives morphological adaptation, and which morphologies may have been the first to evolve in response to a change in locomotion in the earliest hominins.The study enhances research opportunities for undergraduates by directly involving them in data collection and analysis, and involves outreach to the community. Results from this study will be used to develop an evolution lab at a local high school; the lab and scan results will become a permanent resource for students.