Collaborative Research: RUI: The challenges of living small: functional tradeoffs in the vertebral bone structure of diminutive mammals

这项研究探索了身体大小如何影响非常小(微型)哺乳动物的骨骼结构和功能。小型化在动物群体中很常见，而且意义重大，因为它往往与新特征的演变有关，尽管小动物面临着独特的挑战。微型化对脊椎动物骨骼的影响尤其重要，因为骨骼系统支持所有其他器官系统，必须承受内力和外力，同时仍能促进有效的身体运动。最小的脊椎动物的骨骼是如何承受和传递日常力量的，人们仍然知之甚少。3D成像技术、计算机建模和对哺乳动物脊椎(脊椎)的物理测试将被用来评估几个相关的小型哺乳动物群体(地鼠、鼹鼠、刺猬和角齿虎)的骨骼是如何进化成小尺寸的功能的。该项目正在测试较小的骨骼是更坚固(更耐折断)还是更坚硬(更抗弯曲)，以及内部和外部骨骼结构如何协同工作，使非常小的哺乳动物能够安全有效地移动。计划中的活动将促进科学和公众了解自然选择如何导致骨骼形状的变化，以及身体大小如何影响动物与环境互动的方式。该项目涉及对6名来自以本科为主的机构(巴克内尔大学)的学生进行独立研究培训。通过菲尔德博物馆的推广活动将提高公众对小型哺乳动物令人难以置信的多样性和重要性的认识，这些动物经常被忽视，但对生态系统功能至关重要。这项研究利用哺乳动物支系Eulipotyphla的分类丰富以及生态和身体大小的多样性来：1)测量小梁和皮质骨组织对Eulipotyphlan腰椎全骨性能的贡献；2)量化选择压力，以最大化非常小的哺乳动物的骨骼强度和/或僵硬；以及3)确定当非常小的哺乳动物采用新的生态环境时，何时发生强度和僵硬之间的权衡。通过重点研究中轴骨骼，特别是腰椎的骨小梁和皮质骨的形态和性能，这项研究利用了一个系统，该系统在发育上受到HOX模式的限制，但在形态上也是可塑性的，并且严重参与了四足动物的运动。这项研究的综合方法综合了有限元分析(FEA)的结果和身体大小、系统发育、生态和形态测量数据，以评估形态功能的权衡和量化椎骨的选择压力。Eulipotyphla在这一分支范围的功能研究中的使用是新颖但适当的，因为该类群在分类和生态上是多样化的，并且包括按质量计算最小的哺乳动物(重量不到2克)。这些研究将提供新的定量证据，说明骨小梁和皮质骨在压力下的相对重要性和相互作用，并检验长期存在的假设，即选择如何作用于骨形态，以产生适当强度、坚硬的小尺寸骨结构。此外，教育和推广成果包括本科生研究培训，在菲尔德博物馆寻找小型哺乳动物的寻宝活动，以及菲尔德博物馆支持中学学习标准的学习工具包。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。

This research explores how body size affects the structure and function of bones in very small (miniaturized) mammals. Miniaturization is common across animal groups and is significant because it is often associated with the evolution of new features despite the unique challenges faced by small animals. The effects of miniaturization on the vertebrate skeleton are particularly fundamental because the skeletal system supports all other organ systems, and must withstand internal and external applied forces while still facilitating efficient body motion. It remains poorly understood how the skeletons of the smallest vertebrate animals withstand and transmit everyday forces. 3D imaging techniques, computer modeling, and physical testing on mammalian backbones (vertebrae) will be used to assess how the skeletons of several related groups of small mammals (shrews, moles, hedgehogs, and solenodons) have evolved to function at small size. The project is testing whether smaller bones are stronger (more resistant to breaking) or stiffer (more resistant to bending), and how internal and external bone structure work together to allow very small mammals to move safely and efficiently. Planned activities will promote scientific and public understanding of how natural selection leads to changes in the shapes of bones, and how body size influences the way animals interact with their environment. This project involves training of six students from a primarily undergraduate institution (Bucknell University) in independent research. Outreach activities through the Field Museum will promote public awareness of the incredible diversity and importance of small mammals, which are often overlooked but are critical to ecosystem function.This research leverages the taxonomic richness and ecological and body size diversity of the mammalian clade Eulipotyphla to: 1) measure the contributions of trabecular and cortical bone tissues to whole-bone performance in the eulipotyphlan lumbar spine; 2) quantify the selective pressures to maximize bone strength, stiffness, or both in very small mammals; and 3) determine when tradeoffs between strength and stiffness occur as very small mammals adopt novel ecologies. By focusing on the morphology and performance of trabecular and cortical bone in the axial skeleton, specifically the lumbar spine, this research takes advantage of a system that is developmentally constrained via Hox patterning but also morphologically plastic and heavily involved in quadrupedal locomotion. The integrative approach of this study synthesizes Finite Element Analysis (FEA) results with body size, phylogenetic, ecological, and morphometric data to assess morpho-functional tradeoffs and quantify selective pressures on vertebral bone. The use of Eulipotyphla for this clade-wide functional study is novel but appropriate, as the group is taxonomically and ecologically diverse and includes the smallest mammal by mass (weighing less than two grams). These investigations will yield novel quantitative evidence about the relative importance of, and interaction between, trabecular and cortical bone under stress, and test long-standing hypotheses about how selection acts on bone morphology to produce appropriately strong, stiff bony structures at small sizes. In addition, educational and outreach outcomes include undergraduate research training, a treasure hunt activity to find small mammals at the Field Museum, and a learning kit for the Field Museum to support middle school learning standards.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.