Gap crossing is a regular locomotor activity for arboreal animals. The distance between branches likely plays a role in determining whether an animal is capable of crossing a given gap, and what locomotor behavior it uses to do so. Yet, despite the importance of gap distance as a physical parameter influencing gap crossing behavior, the precise relationships between gap distance and movement kinematics have been explored in only a very small number of species. One particularly interesting group of arboreal inhabitants are the flying snakes (Chrysopelea). This species is able to use a dynamic "J-loop" movement to launch its glides, but it is not known whether it is also capable of using such jumps to cross smaller gaps between tree branches. This dissertation addresses this knowledge gap, and investigates the influence of gap distance on crossing behavior and kinematics in three closely-related species of snake: Chrysopelea paradisi, a species of flying snake, and two species from the sister genus, Dendrelaphis, neither of which can glide. Chapter 2 is a literature review of the biomechanics of gap crossing, specifically focusing on the role played by gap distance, and establishes the context for the rest of the work. Chapter 3 presents a detailed study of how increasing gap size influences the behavior and kinematics of gap crossing in C. paradisi, showing that this species uses increasingly dynamic movements to cross gaps of increasing size. Chapter 4 explores the same relationships between gap size and kinematics in D. punctulatus and D. calligastra, revealing remarkable similarities between the three species, suggesting the possibility that dynamic gap crossing may have evolved prior to gliding in this clade. Finally, chapter 5 addresses the role played by gap distance in limiting the non-dynamic, cantilever movements used by these species to cross small gaps, comparing observed stopping distances to those predicted by various torque-related limitations. / Doctor of Philosophy / To successfully cross a gap, an animal must be able to reach or jump from one side to the other. Animals who live in trees must do this quite frequently, as they live among the branches and there are often not connected paths from one place to another. But we don't know very much about how the distance between two structures (the "gap distance") affects the ways an animal moves between them. In this dissertation, I explore how gap distance changes the way a few special species of snakes cross a gap. The species I am studying are special because one species, the paradise tree snake, can glide. Because this 'flying' snake launches its glides by doing a big jump, it is possible that the snake can also jump between tree branches, but this question has never been examined before. We also don't know how the ability to do big jumps evolved, so I studied how distance affects the way two very closely related species of snake, the common tree snake and the northern tree snake, cross gaps. By looking at all of these species, we can understand more about what kinds of behavior are specific to the flying snakes, and which are present in related species. Finally, I also explore how gap distance limits the way the snakes cross gaps when they are not jumping. When the snakes do not jump, they have to hold themselves out straight off the end of a branch. This requires a lot of muscular effort, which means they can't go as far. The fact that the non-jumping behavior is distance-limited might help explain why the snakes need to jump. Altogether, the projects in this study help us understand how gap distance influences what behavior an animal chooses to cross the gap, and increases our knowledge of how flying snakes and their relatives cross gaps in particular.

No description available.