CAREER: Liminal locomotion: life at the air-water-land interface

Pennsylvania State Univ University Park, University Park PA

Investigators

Abstract

This award is funded in whole or in part under the American Rescue Act of 2021 (Public Law 117-2). Most animals are movement specialists: swimmers, walkers, or flyers. But a few species have the unusual ability to move in all of these modes. To be this versatile, a multimodal animal must overcome the significant functional challenge of generating thrust in the divergent physical conditions of water, land, and air. Understanding how animals do this remarkable behavior remains unclear. This project studies trimodal freshwater insects — water boatmen, backswimmers, and diving beetles that swim, walk, and fly — using a biomechanical approach. To visualize the ultrafast motion of their limbs and bodies in 3D, a cutting-edge high-speed video system that can be used in the lab or outside is being developed. During swimming and underwater walking, those limb motions move the water: by tracking precisely how the water moves, the investigator will calculate thrust and gain a mechanical understanding of the behaviors. Comparing three species allows investigation of the different pathways by which the behaviors, and the body shapes that allow them, may have evolved. This research offers insights into the biology of movement versatility and the functional principles needed to invent bioinspired multimodal machines. Graduate students will be trained both in the cutting-edge techniques and in science communication and outreach, helping them integrate public service into their work from the beginning of their research careers. To put outreach into practice, graduate students will partner with two local nature centers to share insights with community members with projects designed to reach different demographics. To understand how some freshwater insects manage to achieve trimodal locomotion, high-speed videography and laser-based flow velocimetry will be combined to build a complete, three-dimensional picture of the kinematics and fluid dynamics of (1) walking in air and underwater, (2) swimming, and (3) the swimming-to-flying transition. Operating at intermediate Reynolds numbers and moving between mediums, the study species offer opportunities to study transitional fluid dynamics, for example, in the scaling of drag-based paddling, a fundamental and widespread locomotor mechanism. This is the first study to measure high-resolution flow fields generated by the swimming of the target species, the first to measure 3D velocity fields of underwater walking in any arthropod, and the first to quantify water takeoff in conjunction with flight in insects. For the takeoff from water to flight, preliminary data suggest that the behavior is driven by both surface tension and aerodynamic forces. This work will shed new light on the general biomechanical principles of free surface locomotion by developing a methodology that permits simultaneous high-resolution temporal and spatial measurement of underwater velocity fields and above-water kinematics. In addition to the important broader impact of graduate student training, this project creates a new learning community for engineering graduate students that will support public outreach efforts, not only for this project, but also for many others, spanning the breadth of the mechanical engineering discipline. These efforts will be assessed as part of an educational study on how graduate students develop into holistic scholars. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.