CAREER: Ontogeny and evolution of avian locomotion: the functional significance of rudimentary structures

该项目将通过探索鸟类基本运动结构的功能相关性来解决一个重要的和长期存在的知识空白。在5亿年的历史中，动物入侵了非常不同的环境，获得了新的身体计划和运动方式。理论可以解释这些身体结构在完全发育的状态下是如何工作的，但是如果结构进化缓慢，通过增量的，适应性的（有益的）阶段，生物体如何获得新的和复杂的结构，这些结构似乎只有在它们完全组装的形式下才有用？换句话说，半只翅膀或半只眼睛有什么好处？这种“两难”的早期或初级阶段一直困扰着进化生物学家，但这是理解生命历史的关键。在发育中的生物和具有退化特征的动物中，对初级阶段的研究较少，但同样重要。退化特征利用不发达的结构在环境中导航，这些结构不仅缺乏专门化，而且往往类似于已灭绝亲属的特征。该项目将通过全面探索三组鸟类的基本运动结构的功能相关性来解决早期阶段的困境：羽翼发育的未成熟鸟类、羽翼减少的成年鸟类和羽翼发育初期的灭绝鸟类。这项研究将通过以下方式增强年轻科学家的能力：(i)在一个大约三分之一的学生是第一代大学生，一半以上是女性的机构中为参与研究的学生提供STEM职业生涯的装备，（ii）将研究纳入课堂并扩大校园博物馆，以及（iii）分享儿童书籍中基本结构的重要性，传授鼓舞人心和相关的教训。高度专门化结构的基本版本是如何运作的？本研究将实地观察与生物力学分析和肌肉骨骼模型相结合，在三个时间尺度上探讨了翅膀的增减：(1)现存发育中的鸟类的初始翅膀。大多数未成熟的鸟类都有“恐龙般的”小翅膀，这对水禽和猎禽的生存至关重要，可能在发育过程中发挥着关键但多样的作用。该项目将研究依赖翅膀的长距离飞行者的运动发育（形态、表现、行为）与先前研究过的更依赖腿的爆发飞行者的运动发育（形态、表现、行为）有何不同。(2)现存鸟类翅膀缩小。由于蜕皮或受伤导致的二级（半）不会飞行或暂时不能飞行的鸟类也有基本的飞行装置，似乎对运动有重要但未被重视的贡献。本项目将量化水禽在二次失飞期间的形态和表现，并记录动物园小翅膀鸟类的行为。(3)灭绝恐龙的原始“翅膀”。鸟类飞行的进化是由带有“原始翅膀”的恐龙化石保存下来的，破译这些化石具有挑战性，但对于理解鸟类的身体计划是不可或缺的。该项目将利用在现存鸟类中建立的生物力学关系来研究一种已灭绝恐龙（始祖鸟）的运动潜力。总的来说，这项研究将解决一个重要的知识差距，促进跨学科的互动，并培养本科生，硕士和博士后水平的学生。结合以上的教育活动，这项工作可以帮助启发未来的科学家创造性地探索沿着生命之树的身体计划的发展和进化。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This project will address an important and long-standing knowledge gap by exploring the functional relevance of rudimentary locomotor structures in birds. Over a 500-million-year history, animals have invaded dramatically different environments, acquiring new body plans and modes of locomotion. Theory can explain how these body plans work in their fully developed states, but if structures evolve slowly, through incremental, adaptive (beneficial) stages, how do organisms acquire new and complex structures that seem to be useful only in their fully assembled forms? In other words, what is the advantage of half a wing or only part of an eye? This “dilemma” of incipient or rudimentary stages has long troubled evolutionary biologists but is key to understanding the history of life. Rudimentary stages are less studied, but equally relevant, among developing organisms and animals with vestigial features, which navigate environments using underdeveloped structures that not only lack specializations, but often resemble features of extinct relatives. This project will address the dilemma of incipient stages by comprehensively exploring the functional relevance of rudimentary locomotor structures in three groups of birds: immature birds with developing wings, adult birds with reduced wings, and extinct birds with incipient “protowings.” The research will empower young scientists by (i) equipping participating students for careers in STEM at an institution where approximately one-third of the students are first-generation college students and more than half are women, (ii) incorporating research into classes and expanding a campus museum, and (iii) sharing the importance of rudimentary structures in a children’s book that imparts an encouraging and relatable lesson.How do rudimentary versions of highly specialized structures function? This research couples field observations with biomechanical analyses and musculoskeletal modeling to explore the gain and loss of wings on three time scales: (1) Incipient wings in extant developing birds. Most immature birds have small, “dinosaur-like” wings, which are vital to survival in waterfowl and gamebirds and likely play a key but diverse role in development. This project will examine how locomotor development (morphology, performance, behavior) in a wing-dependent long-distance flyer differs from that of a previously-studied, more leg-dependent, burst flyer. (2) Reduced wings in extant birds. Rudimentary flight apparatuses also occur in birds that are secondarily (semi)flightless or temporarily so due to molt or injury, and seem to provide important but under-appreciated contributions to locomotion. This project will quantify morphology and performance during a secondary loss of flight in waterfowl, and document behavior in zoo birds with small wings. (3) Rudimentary “wings” in extinct dinosaurs. The evolution of bird flight is preserved by dinosaur fossils with “protowings,” which are challenging to decipher but integral to understanding the avian body plan. This project will use biomechanical relationships established in living birds to investigate locomotor potential in an extinct dinosaur (Archaeopteryx). Collectively, this research will address an important knowledge gap, foster cross-disciplinary interactions, and train students at the undergraduate, Master’s and postdoctoral levels. In conjunction with the educational activities above, this work can help inspire a wide array of future scientists to creatively explore the development and evolution of body plans along the tree of life.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.