Ian K. Bartol (Old Dominion University), Joseph T. Thompson (Saint Joseph's University), and Paul S. Krueger (Southern Methodist University)
Squids are versatile swimmers, having the ability to hover in one spot, change direction or orientation rapidly with apparent ease, and ascend/descend almost vertically. Although squids have fins and arms that are used to varying degrees for propulsion, stability, and maneuverability, it is the pulsed jet that is the foundation of the locomotive system. Pulsed jets in squids, which differ from the more familiar undulatory locomotion of fishes, aquatic reptiles, and aquatic mammals, are generated by alternately filling an internal mantle cavity with water and ejecting that water by powerful mantle contractions through a maneuverable funnel. Pulsed jetting is used by squids of remarkably different sizes, from hatchlings that are only a few millimeters in length to adults that may grow as large as 18 m. Over this wide size range, the physics of fluids plays an important role in the evolution of various jet features (e.g., characteristic vortices known as vortex rings) that are central to propulsive swimming performance. This collaborative project investigates how fluid mechanical constraints shape swimming strategies and muscular mechanics in squid of different life history stages, with the ultimate goal of assessing how propulsive efficiency changes with size. To accomplish this, jet flows, body movements, and muscle properties will be examined in two species of squids, the brief squid Lolliguncula brevis and the oval squid Sepioteuthis lessoniana. These squids, which vary in total length from < 1 cm as hatchlings to >15 cm as adults, will be trained to swim in a flow tank (i.e., an aquatic "treadmill") containing water seeded with light-reflective particles. As particle-laden water is expelled from the funnel, it will be illuminated with lasers and videotaped so that the jet velocity can be determined using a technique known as digital particle image velocimetry (DPIV). These DPIV data will provide direct measurements of jet features and propulsive efficiency. Multiple video cameras positioned on a motorized rail system will be used to collect high-resolution images of the mantle and funnel as the squids swim, providing valuable data on swimming behavior. Because the contractile properties of the mantle change with size and have direct effects on jet flows, detailed measurements of isolated bundles of mantle muscle also will be made using standard muscle mechanical techniques. The integration of DPIV, swimming footage, and muscle mechanical data promises to broaden our understanding of propulsive efficiency in jet-propelled organisms, especially at low size ranges where little is known about the jet mechanism, and provide insight into the evolution of ontogenetic changes in musculoskeletal support systems. These data are relevant not only for biological investigators but also for engineers and designers of emerging technologies, such as synthetic jets and pulsed-jet micro-vehicles. This project will engage undergraduate and graduate students in interdisciplinary research. It will also facilitate minority student involvement, either through direct participation in experiments or through educational development in local public schools and aquariums.
