DISSERTATION RESEARCH: Independent evolution and ancestral conditions in the gnathostome axial column

脊椎动物与无脊椎动物的区别在于，脊椎动物的脊椎骨即使只由软骨构成。尽管它在所有有颌骨脊椎动物的身体平面中处于中心位置，但脊椎的早期进化史和发育机制还没有被很好地理解。在不同的脊椎动物群体中，特别是在鱼类中，组成脊椎的脊椎在形状、组成和结构上都有显著的差异。此外，主要鱼类群体的早期化石记录表明，许多鱼类进化出的脊柱基本成分完全独立于其他鱼类。该项目的目标是记录鲨鱼和溜冰鞋等研究较少的群体中脊椎的发育，确定脊椎的深层历史中实际上发生了多少独立进化，并与目前对骨鱼脊椎发育的理解进行必要的比较。该项目将颌骨超树上的祖先状态重建与计算机断层扫描、基因表达和命运图谱实验相结合，以研究鱼类脊椎进化和发育的宏观进化模式。软骨鱼类是拟议研究的主要焦点，因为它们作为与骨鱼最接近的外群在系统发育中占有关键地位。在发育和功能研究中，软骨动物通常被认为是祖先脊椎动物状况的样本，但它们的许多形态的原始或衍生状态尚不清楚，因此重新成为研究兴趣的主题。确定轴柱复合体中的祖先条件和同源性，对于从另一种脊椎动物模型系统获得的研究和数据的知情评估至关重要。此外，鲨鱼和化石都是极具魅力的研究对象，有效地吸引了公众的兴趣。为了帮助向公众传达这个项目和其他相关项目的性质，研究人员将使用计算机断层扫描(静态和动态)和鲨鱼化石标本来教育当地学校的学生进化生物学的重要性和相关性。

The presence of a backbone, even if only made of cartilage, is the feature that distinguishes vertebrate animals from their invertebrate relatives. Despite its central position in the body plans of all jawed vertebrates, the early evolutionary history and developmental mechanisms that gave rise to the vertebral column are not well understood. Across different vertebrate groups, and among fishes in particular, the vertebrae that make up the backbone are remarkably varied in their shape, composition, and structure. Furthermore, the early fossil record of the major groups of fishes shows that many evolved fundamental components of the vertebral column quite independently of others. The goals of this project are to document vertebral development in poorly studied groups such as sharks and skates, to determine how much independent evolution actually occurred in the deep history of vertebrae, and to provide essential comparisons with the current understanding of vertebral development in bony fishes.This project combines ancestral state reconstructions on gnathostome supertrees with computed tomography, gene expression, and fate mapping experiments to investigate the macroevolutionary patterns of vertebral evolution and development in fishes. Chondrichthyans are the main focus of the proposed research because they occupy a key phylogenetic position as the most proximate outgroup to the Osteichthyes. Chondrichthyans are often considered exemplars of ancestral vertebrate conditions in developmental and functional studies, but the primitive or derived status of much of their morphology is unclear and the subject of renewed research interest. Identifying ancestral conditions and homoplasy in the axial column complex is essential for the informed evaluation of studies and data obtained from alternative vertebrate model systems. Moreover, sharks as well as fossils are charismatic study subjects that effectively capture public interest. To help communicate the nature of this and other related projects to the public, the investigators will use computed tomographic scans (static and animated), and fossil shark specimens to educate students at local schools about the importance and relevance of evolutionary biology.