Locomotor Ontogeny in Microcebus Murinus, Petaurus Breviceps and Monodelphis Domestica: The Influence of Very Small Body Size on the Evolution of Primate Quadrupedal Locomotion

这项研究为灵长类起源的研究带来了一个新的视角，通过研究非常小的身体尺寸对灵长类运动适应进化的影响。现存的灵长类动物表现出一系列不同的特殊运动行为，但大多数在它们的运动技能中包括四足行走。灵长类动物使用的四足行走形式在哺乳动物中是不寻常的，被认为是当最早的灵长类动物与他们的哺乳动物祖先背道而驰时出现的一种进化创新。目前的共识是，灵长类四足动物的特征是一种生物力学复合体，通过在小而不稳定的树枝上提供平衡机制，使早期灵长类动物能够独占地获得树栖“细小树枝生态位”中可用的资源。在灵长类四足动物进化的研究中，一个经常被忽视的重要问题是身体大小与底物(例如分支)大小的相互作用。显然，对于小型和大型灵长类动物来说，“细枝生态位”带来的运动挑战不能被认为是相同的。如果不考虑身体大小与底物大小的关系，我们就无法理解灵长类四足动物的运动进化。最近关于灵长类祖先大小的争论包括这样一种观点，即祖先灵长类可能比现存的最小的灵长类(老鼠狐猴)小得多，可能只有10-15克，但很少有研究考虑身体大小为100克或更少对灵长类四足动物的影响。这项研究将以运动生长发育为手段，研究非常小的身体尺寸对灵长类运动进化的影响。结合对两种小型有袋类动物运动发育的研究，将比较幼年和成年鼠狐猴(Microcebus Murinus)在各种基质上的四足动物运动，这两种小型有袋类动物是树栖糖滑鼠(Petaurus Brevicep)和陆栖灰色短尾负鼠(Monodelphis Home Tica)。产后稳定的婴儿将被用来检验关于身体尺寸和底物类型减少对四足动物运动的影响的假说。此外，从最小的婴儿期到成年期的形态和运动的发育转变将被用来检验关于身体形状对四足畸形的生物力学影响的假说。在灵长类或有袋类动物中，很小的身体尺寸对灵长类四足动物的影响以及“细枝生态位”的影响在很大程度上仍未被研究。这项研究将首次将发育分析与灵长类四足动物的运动研究结合起来，从非常小的身体尺寸的角度研究灵长类四足动物的运动，并首次从生态学和进化的角度研究小头鲸、斑头龙和斑腿猴的运动发育。这项研究将加强德克萨斯大学奥斯汀分校的本科教育，因为糖滑翔机和老鼠狐猴将被安置在一个观察室里，供学生为人类学和生物学课程收集行为数据。将加强对一名博士后助理和参与该项目的学生的研究培训。结果将被纳入教育电子实验室模块，原始数据将提供给其他研究人员。德克萨斯大学奥斯汀分校、西南国家灵长类研究中心和杜克大学之间的合作将得到加强。

This study brings a new perspective to the study of primate origins by examining the influence of very small body size on the evolution of primate locomotor adaptations. Living primates exhibit a diverse array of specialized locomotor behaviors, but most include quadrupedalism in their locomotor repertoire. The form of quadrupedal walking used by primates is unusual among mammals, and is thought to have arisen as an evolutionary innovation when the earliest primates diverged from their mammalian ancestor. Current consensus states that primate quadrupedal features are a biomechanical complex that gave early primates exclusive access to resources available in an arboreal "fine branch niche," by providing mechanisms for balance on small and unstable branches. One important issue often overlooked in research on the evolution of primate quadrupedalism is the interaction of body size with substrate (e.g., branch) size. Clearly, the locomotor challenges presented by the "fine branch niche" cannot be assumed to be the same for small and large primates. We cannot understand the evolution of primate quadrupedal locomotion without considering body size relative to substrate size. Recent debate on primate ancestral size includes the view that ancestral primates may have been much smaller than the smallest living primates (mouse lemurs), perhaps as small as 10-15g, yet few studies have considered the effects of body sizes of 100g or less on primate quadrupedalism. This study will use locomotor growth and development as a means to investigate the influence of very small body size on primate locomotor evolution. Quadrupedal movement on a variety of substrates will be compared between and within infant and adult mouse lemurs (Microcebus murinus) in conjunction with a study of locomotor development in two small-bodied marsupials, the arboreal sugar glider (Petaurus breviceps) , and the terrestrial gray short-tailed opossum (Monodelphis domestica). Posturally stable infants will be used to test hypotheses regarding the effects of reduced body size and substrate type on quadrupedal movement. In addition, developmental transitions in morphology and locomotion from youngest infancy to adulthood will be used to test hypotheses about the biomechanical effects of body shape on quadrupedalism. The influence of very small body size on primate quadrupedalism and in the context of the "fine branch niche" remains largely unexplored in either primates or marsupials. This study will be the first to combine developmental analysis with an examination of primate quadrupedal locomotion from the perspective of very small body size, and the first to address locomotor development in Microcebus, Petaurus, and Monodelphis from an ecological and evolutionary perspective. This study will enhance undergraduate education at UT Austin, as the sugar gliders and mouse lemurs will be housed in an observation room utilized by students collecting behavioral data for anthropology and biology courses. Research training will be enhanced for a postdoctoral associate and students participating in the project. Results will be incorporated into an educational electronic lab module, and raw data will be made available to other researchers. Collaboration between UT Austin, Southwest National Primate Research Center, and Duke University will be strengthened.