Thesis (Ph.D.)--University of Washington, 2023Chondrichthyes (chimaeras, sharks, skates and rays) are a lineage of vertebrates with skeletons composed entirely of cartilage, that have existed for over 400 million years. This long evolutionary history has allowed them to diversify their life-history traits, ecology, and biogeography as they are found throughout the world’s marine and freshwater waterways. Two critical aspects of an organism’s life are reproduction and locomotion. Chondrichthyans exhibit most forms of sexual reproduction, from egg-laying to live birth: oviparity, multiple types of aplacental viviparity, and placental viviparity. They also evolved many modes of locomotion, from axial-swimming (tail undulations), undulating or oscillating pectoral fins, to walking (or ‘punting’) along the substrate with pelvic fins. Some species use a combination of these methods to locomote, depending on their habitat. Aside from using cartilaginous fishes as my model, the tie between all of my chapters are the principles of form and function. How does the change in skeletal morphology influence how an animal moves and how is that driven by where it lives; habitat structuring encompasses what an organism encounters, to eat or avoid being eaten, it can also be reflective of where they reproduce and how long it takes to develop. Each chapter plays off these principles and flows into the next. First, I consider chondrichthyan evolution and life-history traits, what came before and has shaped what remains today; what characteristics don’t evolve in specific regions and ranges, and why might this be? Next, I consider the hydrodynamics of egg cases from multiple species of skates (Rajiformes) to determine how species-specific traits, specifically macro-morphology and microstructure, contribute to the variation where these eggs occur in order to aid in protective policies to avoid disturbing nursery grounds. Lastly, I characterize the swimming kinematics of the spotted ratfish (Hydrolagus colliei, Holocephali). Chimaeras are thought to move via pectoral fin-based swimming, flapping and fluttering their large fins in order to propel themselves through their deep dark world. But, chimaeras also have prominent pelvic fins, which allows us to compare the relationship between these two sets of fins, and the reliance of both sets during variable swimming conditions. In summary, I use Chondrichthyes as my system to understand how an ancient lineage of fishes live and move through their environments
