Pursuit and Evasion Strategies in Zebrafish: Mathematical Modeling and Behavioral Experiments

Author(s): Soto, Alberto Prado | Advisor(s): McHenry, Matthew J | Abstract: Predator-prey interactions are important to the ecology and evolution of animals and have major implications for the behavioral and locomotor strategies they exhibit. They offer a system to study the strategies used by animals to pursue prey and evade predators from both a theoretical and experimental perspective. Here I have mathematically modeled the evasion strategy of prey fish, conducted experiments to assess the pursuit strategy of zebrafish, and developed a technique to investigate the biomechanics of fish locomotion during pursuit. My first dissertation chapter revisited the mathematics of a classic pursuit-evasion model and tested the predictions against empirical data on the escape response of larval zebrafish. The evasion strategy of prey in response to an approaching predator had been previously modeled and predicted an optimal escape direction based on the relative speed of the prey, but empirical results often failed to confirm the model predictions. I revisited and generalized the model to reveal a large region of parameter space that predicted a previously unknown performance plateau. The plateau indicated that fast prey can escape away from a slower predator in many directions without diminishing their escape performance. I tested the model predictions against data on the escape direction of larval zebrafish in response to an approaching robotic predator and found general agreement. Chapter two of my dissertation focused on the pursuit strategy of zebrafish in pursuit of prey. To study the locomotion of zebrafish chasing prey, I built an experimental setup to film predator--prey interactions at high--speed. These interactions were automatically analyzed with a custom image processing algorithm that tracks the midline of the predator and the position of the prey through time. I confirmed that zebrafish swim intermittently in a burst--and--coast swimming pattern during pursuit. The predator turned and accelerated toward the prey with a single tail beat. The change in heading during a turning maneuver could be predicted by the bearing angle immediately before the burst phase and was correlated with the lateral excursion of the caudal fin. This intermittent pursuit strategy is a form of pure pursuit in which the predator aligns its heading with the position of the prey. My third dissertation chapter developed a technique to acquire multichannel imaging data using a single camera. In chapter two, I found that zebrafish predators execute turning maneuvers that orient them toward the position of the prey. A mechanistic understanding of how fish execute turning maneuvers continues to elude biologists and physicists alike because it requires measuring the forces produced by the swimming fish. I addressed this challenge by designing an experimental system which allows for simultaneous acquisition of images for flow visualization and automatic tracking using a single high--speed video camera. This technique, Multichannel Stroboscopic Videography (MSV), provides the ability to automate measurements of both the animal's body and flow field and illustrates MSV's powerful capacity for high-throughput experimentation with a complex hydrodynamic analysis.