My research interests are in the fields of functional morphology and ecological physiology. My focus is in the study of the dynamics of locomotion in animals. I examine the energetics and hydrodynamics of vertebrate swimming, with particular regard to propulsive modes and the evolution of aquatic mammals. This research is accomplished by examination of morphological structures with computer tomography (CT scans), biomechanics with motion analysis and computer digitizing, and exercise physiology by measurement of metabolic performance with oxygen consumption. Research in the Liquid Life Lab has allowed my students and me to work with a variety of animals, including whales, dolphins, seals, sea lions, mantees, otters, platypus, muskrat, beaver, opossums, hippopotamus, frogfish, flying fish, sharks, mallard ducks, alligators, and whirligig beetles. The research has been funded by the National Science Foundation (NSF), Office of Naval Research (ONR), and Defense Advanced Research Projects Agency (DARPA). The research has application in the field of biomimetics and bioinspiration of engineered systems. I am currently on the editorial board of the journal Bioinspiration and Biomimetics, which is published by the Institute of Physics.
I have been profiled for my research in the book At the Water's Edge: Macroevolution and the Transformation of Life by Carl Zimmer. I have appeared on television in the PBS series Evolution and in the BBC production of Walking with Prehistoric Beasts, which aired on the Discovery Channel.
Research Topics
Thermoregulation in aquatic animals
The aquatic environment presents challenges to animals that control their body temperture. Water is thermally more conductive than air at the same temperature. To maintain a body temperature above the temperature of the water, aquatic animals must either increase their metabolism, increase the insulation of the body, or find new sources of thermal energy.
My Master's thesis research examined the changes in insulation associated with the regulation of metabolism in the muskrat (Ondatra zibethicus). The fur of the muskrat insulates the body, but cannot be regulated. By using regional heterothermia, the muskrat could regulate the temperature of the appendages (feet, tail), with their high surface-to volume ratio, and adjust its thermal insulation. When heat needs to be conserved and insulation increased, blood flow to the appendages is reduced and the appendage takes on the temperature of the environment. In water, the muskrat allowed its appendages to approach the temperature of the medium. In air at high temperatures, the appendages were warmed once the core body temperature reached a critical level. The temperature of the appendages cycled with the core temperature.
Fish, F. E. 1979. Thermoregulation in the muskrat (Ondatra zibethicus): The use of regional heterothermia. Comparative Biochemistry and Physiology 64A(3): 391-397. pdf
Jet Propulsion
Locomotion in animals by jet propulsion is typically associated with the pulsing movements of the jellyfish or the rapid movements of squid and octopus. Jetting is less common in vertebrates, but is used by some species of fishes. The frogfishes (Genus Antennarius) has restricted opercular openings in the axilla of the pectoral fins. As the fish breathes, it can expel water from the opercular openings as jets. The frogfish can use the jets to take-off from the bottom or to move through the water (below). Due to the high drag of the body, the fish jets at low speeds of 2.3-2.7 cm/sec (0.27-0.32 body lengths/sec). Because the jets are located under the center of gravity of the body, the head of the fish pitches up and down, during expiration and inspiration, respectively. Jetting may be a strategy by the frogfish to sneak up on its prey. Frogfishes mimic sponges and rocks. When the frogfish gets close enough to its prey, it waves the first dorsal fin spine, which has a lure on its end. Once the prey approaches, the frogfish can rapidly engulf the prey.
Fish, F. E. 1987. Kinematics and power output of jet propulsion by the frogfish genus Antennarius (Lophiiformes: Antennariidae). Copeia 1987(4): 1046-1048. pdf
Energetics of Swimming
Stability and Maneuverability
The morphological designs of animals represent a balance between stability for efficient locomotion and instability associated with maneuverability. Morphologies that deviate from designs associated with stability are highly maneuverable . Major features affecting maneuverability are positions of control surfaces, control of buoyancy, and flexibility of the body. For marine mammals, variation in body design affects stability and turning performance.
Sirenians, such as manatees, have a high degree of hydrostatic control over buoyancy and thus are able to control stability without flow induced lift forces to stabilize body orientation and with a minimum of control surfaces (i.e., flippers, flukes).
Cetaceans have a number of control surfaces (i.e., flippers, flukes, dorsal fin, caudal peduncle) and relatively rigid body that provides a generally stable design. Destabilizing forces generated during swimming are balanced by dynamic stabilization due to the phase relationships of various body components. Cetaceans with flexible bodies and mobile flippers (Dephinapterus, Inia) are able to turn tightly, although at low turning rates, compared to fast-swimming cetaceans (Lagenorhynchus, Cephalorhynchus, Orcinus) with less body flexibility and relatively immobile flippers. This latter group sacrifices small turning radii for higher turning rates. In cetaceans, turning performance and the morphology and placement of control surfaces are associated with prey type and habitat. Flexibility and slow, precise maneuvering are found in cetaceans that inhabit more complex habitats (i.e., rivers, pack ice), whereas high-speed maneuvers are used by cetaceans in the more open pelagic environment. As smaller prey species, such as fish, can produce smaller radius turns at higher turning rates than dolphins, these fast-swimming dolphins compensate by working in cooperative groups or by using maneuvers in which they orient the body to easily bend and bring the mouth toward the fish rapidly.
Evolution of Swimming Modes
For secondarily aquatic vertebrates, the movement from the terrestrial environment back into the water was a major evolutionary change.
Three-Dimensional Geometry of Biological Control Surfaces
The immense diversity of animals with their particular morphological features presents a rich resource of novel designs that may be incorporated into advanced technologies. The technology associated with the development of robots is becoming more dependent on biomimetics and biologically-inspired designs. The morphology of animals have been copied for development of various technologies. Both machines and animals must contend with the same physical laws that regulate their design and behavior. These behaviors (i.e., maneuverability, acceleration) can be superior to the performance of machines.
The control surfaces of animals have different functions including propulsion, maneuverability, braking, trim control, hovering, reverse swimming, and stability. In nature, the control surfaces are used for prey capture, prey acquisition, escape maneuvers, obstacle avoidance, turning in restricted spaces, surfacing, diving, and control of rapid accelerations. Stealth may be an important characteristic of maneuvering with pectoral fins as prey acquisition by a predator often requires approach without detection. Various morphologies within aquatic animal lineages have evolved which foster maneuverability. Turning performance can be affected by morphology with respect to rigidity of the body, and mobility and position of the control surfaces (e.g., fins, paddles, flippers) determining the level of performance.
Despite the importance of the control surfaces, there has been little information on the structure, function, and hydrodynamics of aquatic biological control surfaces. A description of the morphological variation and three-dimensional geometry of the control surfaces of nektonic organisms would be beneficial to both biologist and engineers.
My research on the control surfaces has used medical computer tomography (CT) scans to examine the three-dimensional geometry for a variety of vertebrate species, including dolphins, whales, porpoises, manatee, sea lion, seals, penguins, sea turtles, tuna, sharks and rays.
Comments or Suggestions? email Webmaster