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

古人类双足行走的进化标志着我们谱系的起源，并代表了运动模式和肌肉骨骼形态的重大转变。 然而，支撑这种运动转变的进化机制尚不清楚，竞争模型表明不同的选择压力导致了双足特征的产生。 博士生 Adam Foster（亚利桑那大学）在 David Raichlen 博士的指导下进行的研究将确定形态对行为做出反应的模式，从而有助于我们对双足进化的理解。 该研究使用大鼠模型，直接测试了机械负载的数量和方向（从四足站立和运动到双足站立和运动的转变）在个体发育和成年期颅后骨骼中产生适应性形态的作用。 该研究探讨了三个主要问题：（1）双足站立和/或双足行走在骨骼形态适应性变化中起什么作用，（2）个体发育（即发育可塑性）在适应性双足形态产生中的作用是什么，以及（3）个体发育过程中与运动变化相关的形态变化会影响运动学和能量学吗？ 大鼠将被放置在安装在跑步机上的定制安全带系统中，当跑步带不运动时，该系统允许舒适的双足运动或静态负载，并且将每天运动或站立一小时，每周 5 天，持续 90 天。 通过微型 CT 扫描跟踪骨骼变化，运动学和能量学数据检查与形态变化相关的潜在能量成本降低。 这些发现将有助于确定行为如何驱动形态适应，以及哪些形态可能是最早响应最早古人类运动变化而进化的。这项研究通过直接让本科生参与数据收集和分析，并涉及到社区的推广，增加了本科生的研究机会。 这项研究的结果将用于在当地一所高中建立一个进化实验室；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.