This research will investigate the fluid mechanics of aquatic suction feeding, the most commonly used method of prey capture among vertebrate animals. Suction feeding is found in aquatic species of every major group of land-dwelling vertebrates, and is the principal prey-capture mechanism used by bony fishes, a group that makes up over half of all vertebrate species. This behavior involves the explosive expansion of the mouth and oral cavity to accelerate water and prey into the mouth. Suction flows exert forces on prey, transporting them to the predator, and these flows determine the success of suction feeders. Because of the technical challenges associated with observing high-speed water motion, very few direct observations of suction feeding flows have been made. The purpose of this project is to study these water flow patterns using new technologies and to study the mechanics of predator prey interactions. By contributing basic knowledge about how animals manipulate the water they live in to capture food this research will contribute to our understanding of a major period in vertebrate evolution and will deepen our insight into the relationship between skull design and feeding ecology and evolution in teleost fishes. A mathematical computational fluid dynamic model will be further developed and used in conjunction with experimental flow visualization by Digital Particle Image Velocimetry (DPIV) to characterize the temporal and spatial distribution of suction flows and how they influence suction feeding performance. DPIV uses a laser light sheet about 5 cm in width and 2 mm thick to illuminate neutrally buoyant particles in the water. High speed video (500 - 1000 images/s) is directed at this light sheet and water motion is visualized by tracking the particles suspended in the water. Computer programs are used to precisely infer water velocity patterns by analyzing consecutive video images of particle motion. The effect of forward swimming behavior during suction feeding (termed 'ram feeding') on the water flow pattern created by suction will be measured. In addition, the forces exerted on prey by suction flows will be measured both by inferences from the water flow patterns and directly through the use of force transducers to test the hypothesis that the acceleration reaction, a previously ignored force that is generated by flows of changing velocity, outpaces the more familiar drag forces that are experienced by prey caught in a flow. An important role for acceleration reaction may greatly alter the picture of forces that are experienced by prey, and may help to explain the explosive nature of suction feeding, which can occur in less than 10 msec, one of the fastest feeding behaviors seen in vertebrates. A second part of the project will be directed at understanding the variation among fish species in suction feeding performance. Four species in the freshwater fish family Centrarchidae will be studied representing the range of suction feeding abilities known in this family. A parallel series of four species of the Cichlidae representing a similar range of ecomorphological diversity will also be studied. Peak suction flow capacity will be measured for each species using DPIV while mouth and oral expansion will be measured using an ultrasound method, sonomicrometry, that permits precise quantification of changes in the internal dimensions of the oral cavity during feeding. Broader impacts of this project may involve application of information on unsteady flows to enhance forces exerted on target bodies in the development of surgical suction devices. This research will provide training for a postdoctoral researcher, a female graduate student, and an undergraduate from an underrepresented group. The postdoc will gain teaching experience and the graduate student will design a laboratory exercise on aquatic feeding for use in a course on vertebrate evolution. A website will be developed that provides information about suction feeding and movie clips of feeding fish for use by university instructors in organismal biology courses.
