CAREER: Evolutionary biomechanics and functional morphology of salamander locomotion

四足动物四足动物是如何变成陆地动物的，这是脊椎动物进化中的一个关键事件，为此后四足动物的多样化奠定了基础。早期四足动物的运动能力通常是用现存的火蜥蜴来模拟的，因为后者有一个广义的四足动物身体规划。然而，火蜥蜴在不同环境中表现出巨大的形态多样性，通过比较仔细匹配的进化谱系中的形态变化，提供了一个框架来评估陆地运动的机械要求。重力的更大影响可能会施加生物力学限制，阻止某些火蜥蜴在陆地上活动，但不同的发展战略，火蜥蜴占据的栖息地不同。变态包括动物在两个或更多不同的生命阶段的发育，但可以是双相(水生幼虫到陆生成虫)或多阶段(水生幼虫到陆生幼虫到水生成虫)，而直接发育保持在一个环境中。因此，生物力学约束在陆相直接显影剂中可能比双相变质者更强，因为前者不经历水生阶段。该项目将整合生理学、工程学和进化生物学，以研究栖息地偏好和发展战略之间的相互作用如何影响组织(例如骨骼)的结构和功能与整个有机体性能(例如运动)之间的关系。学生将通过一个新的以课程为基础的本科组织形式和功能研究经验和生物学学士后专业研究经验课程接受研究培训，以扩大来自历史上被排斥的社区的学习者的参与。此外，还将在两栖动物周期间举办“火蜥蜴之旅”活动，以促进女孩参与STEM。运动对骨骼提出了一些最高的身体要求(负荷)，无法承受负荷可能会导致动物骨折甚至死亡，然而骨骼如何进化来支持水生环境与陆地环境施加的负荷还不是很清楚。对生态不同物种的全骨力学进行系统发育比较，将促进人们对栖息地和发展战略如何塑造蜥蜴肢体骨骼进化形态的了解。研究人员将通过同步的3D运动学和动力学来量化陆地行走过程中的活体骨骼负荷。然后，研究人员将应用这些载荷数据，通过结合力学性能测试和3D数字图像关联来收集肢体骨强度的第一个动态测量数据。最后，他们将结合这些技术，通过比较不同发展策略(即直接、双相、多相)物种的幼体和成年动物，来研究一生中水-陆和陆-水转换对骨骼力学的影响。据预测，陆地直接显影剂的骨强度最高，有足形态的水生火蜥蜴最低，双相变质火蜥蜴居中。更强壮的骨骼可能有助于陆地物种承受内部(肌肉)和外部(地面反作用力)负载，然后将这些能量转化为推进。与股骨相比，基于前肢的多功能作用(例如，挖掘、繁殖、运动)，前肢预计将以更快的速度进化，与后肢相比，前肢的约束可能较少，后肢的主要作用是产生推进力。这项工作的发现将有助于对成为陆地的机械要求提供新的见解。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

How tetrapods, four footed animals, became terrestrial was a pivotal event in vertebrate evolution that set the stage for the diversification of tetrapods thereafter. The locomotor capabilities of early tetrapods are often modeled with extant salamanders since the latter have a generalized tetrapod body plan. Yet, salamanders exhibit tremendous morphological diversity across environments, providing a framework to assess the mechanical requirements for terrestrial locomotion by comparing morphological change across carefully matched evolutionary lineages. The greater effects of gravity may impose biomechanical constraints that preclude certain salamanders from moving on land, but the habitat that salamanders occupy differs between developmental strategies. Metamorphosis involves the development of an animal across two or more distinct life stages but can be biphasic (aquatic larvae to terrestrial adults) or multi-phasic (aquatic larvae to terrestrial juveniles to aquatic adults) whereas direct development remains in one environment. Thus, biomechanical constraints may be stronger in terrestrial direct developers than biphasic metamorphers since the former do not experience an aquatic stage. This project will integrate physiology, engineering, and evolutionary biology to examine how the interplay between habitat preference and developmental strategy affects the relationship between the structure and function of tissues (e.g., bones) and whole-organism performance (e.g., locomotion). Students will receive research training through a new Course-Based Undergraduate Research Experience on Organismal Form and Function and Professional Research Experience for Post-baccalaureates in Biology program to broaden the participation of learners from historically excluded communities. In addition, “Salamander Safaris” will be hosted during Amphibian Week to promote the participation of girls in STEM. Locomotion places some of the highest physical demands (‘loads’) on bones and failure to withstand loads could cause fractures or even death in an animal, yet how bones evolved to support the loads imposed by aquatic vs. terrestrial environments is not well understood. Phylogenetic comparisons of whole-bone mechanics across ecologically diverse species will advance knowledge of how habitat and developmental strategy has shaped the evolutionary morphology of salamander limb bones. Investigators will quantify in vivo bone loading during terrestrial walking through synchronized 3D kinematics and kinetics. Investigators will then apply these loading data to collect the first dynamic measures of limb bone strength by integrating mechanical property testing and 3D digital image correlation. Finally, they will combine these techniques to examine how bone mechanics is affected by water-land and land-water transitions within a lifetime by comparing juveniles and adults from species with different developmental strategies (i.e., direct, biphasic, multiphasic). Bone strength is predicted to be highest in terrestrial direct developers lowest in paedomorphic aquatic salamanders, and intermediate in biphasic metamorphic salamanders. Stronger bones likely assist terrestrial species to withstand internal (muscle) and external (ground reaction forces) loads and then transfer this energy into propulsion. Compared to the femur, the humerus is expected to evolve at faster rates based on the multi-functional role of forelimbs (e.g., digging, reproduction, locomotion) that is likely less constrained compared to hindlimbs whose primary role is for generating propulsion. Findings from this work will contribute new insights into the mechanical requirements of becoming terrestrial.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.