Anti-Predator Responses of Squid Throughout Ontogeny

Multiple sensory modalities and a complex array of escape behaviors have evolved as components of anti-predator responses in squids. The goals of this study include: (1) examine the role of the lateral line analogue and vision in successful predator evasion; (2) measure kinematics of escape jetting; (3) document how chromatic patterning, posturing and inking in squid change in response to predators; and (4) investigate escape jet hydrodynamics of squid. Given that squids undergo considerable morphological, ecological, and behavioral changes throughout ontogeny, the goals above were all investigated across different life history stages. To test the respective roles of vision and the lateral line analogue, squid of different life stages were recorded in the presence of natural predators under light and dark conditions with their lateral line analogue intact and ablated via a pharmacological technique. Anti-predator behaviors of squid throughout ontogeny were studied in a series of predator-prey trials using high-speed videography. Additionally, the hydrodynamics and kinematics of high velocity escape jets in squid were examined using a combination of 2D/3D velocimetry. The lateral line analogue played a role in initiation of an escape response at the earliest life stages, and continued to contribute to successful evasion by aiding visual cues in juvenile/adult squid. Paralarvae relied heavily on stereotyped swimming behaviors and translucent coloration to avoid capture, while juvenile and adults used multiple cues associated with the predator’s approach to determine whether posturing or inking and escape jetting is the most suitable anti-predator behavior. Throughout ontogeny, squid produced two escape jet patterns: (1) escape jet I characterized by short rapid pulses resulting in vortex ring formation and (2) and escape jet II characterized by long high volume jets, often with a leading edge vortex ring. Paralarvae exhibited significantly higher propulsive efficiency (94.55%) than adult squid (87.71%) during jet ejection. These results indicate that all life stages of squid are well adapted for predator avoidance; they employ multiple sensory modalities for predator detection, use a variety of anti-predator behavioral responses, and utilize a highly efficient and flexible escape jet to maximize escape from predation