Deban Lab Research

Physiology and Biomechanics of Movement

Our research examines how organisms move during feeding and locomotion, and how physiological and biomechanical function changes through evolution. You can read about some of our projects in the brief summaries below.

Ballistic Tongue in a Miniaturized Salamander

Miniaturization of body size is often accompanied by peculiarities in morphology that can have functional consequences. We examined the feeding behavior and morphology of the miniaturized plethodontid salamander Thorius, one of the smallest vertebrates, to determine if its performance and biomechanics differ from those of its larger relatives. We found that its tongue is ballistic and achieves accelerations of up to 600 G with low thermal sensitivity, indicating that tongue projection is powered by an elastic-recoil mechanism, like its larger relatives. Due to its small size, Thorius possesses a reduced number of myofibers in the tongue muscles, a large projector muscle mass relative to tongue mass, and an unusual folding of the tongue skeleton. See our paper in the Journal of Experimental Zoology.

Extreme Salamander Biting Force

We modeled the biting capacity of salamanders by analyzing the geometry of the skull, jaws and head muscles. We found that dusky salamanders amplify their biting force by using a unique and historically enigmatic system of ligaments that couples head movements with jaw movements. This mechanism allows the salamanders to supplement their jaw muscles with other muscles and increase their biting force more than five times. To analyze the salamander jaws, we developed a novel 3D geometric method for determining muscle moments using linear measurements of skeletal material, without the need for 3D coordinate data. See our paper in the Journal of Experimental Biology for details of the unique jaw mechanism and our methods.

Functional Tradeoffs in Aquatic Feeding

During aquatic feeding, salamanders use the hyobranchial apparatus to expand the mouth cavity and generate suction that draws in prey. Among newts of the family Salamandridae there is a wide range of ecological diversity: species are terrestrial, semi-aquatic, or aquatic as adults. We tested if a more robust hyobranchial apparatus yields increased aquatic feeding performance. Using digital particle image velocimetry (PIV), we found that fluid velocity (figure) generated in the fully aquatic Paramesotriton, which has the most robust hyobranchial apparatus, was double that of all semi-aquatic species. These findings reveal that specialized morphology increases aquatic feeding performance in newts. See our paper in Zoology.

How Muscles Respond to Conditions

Performance of muscle-powered movements depends on temperature of the muscle and the force the muscle must develop. In our experiments on frog limb muscles, we found that muscle velocity, power and work are most strongly affected by temperature at low temperatures and high forces. These results suggest that animal performance that requires muscles to do work with low forces relative to a muscle's maximum force production will be robust to temperature changes. Conversely, performance requiring muscles to shorten with relatively large forces is expected to be more sensitive to temperature changes. See our paper in the Journal of Experimental Biology.

Interactive Muscle-Spring Model

Our interactive muscle model integrates the physiological properties of muscle tissue with the mechanics of elastic recoil to predict performance of movement. The model uses forward dynamics and Runge-Kutta integration, and is implemented in JavaScript in the browser. The physiological and mechanical inputs to the model can be changed interactively and the results are immediately visible and downloadable as tabular data. The model is designed to be useful for exploring hypotheses regarding the function of integrated systems and for teaching students the principles of muscle-powered movement. See our GitHub repo for the public code or play with the model.

High-Power Ballistic Movements

The photo below of a Hydromantes shooting its tongue to catch a housefly reveals the spectacular performance of some ballistic movements. The tongue skeleton is acting like a harpoon and is shot completely from the salamander’s body. The tongue is projected so rapidly that it travels to the prey under its own momentum. We are examining tongue projection as a model of ballistic movement and have found that tongue projection in salamanders is accomplished with extremely high power output via an elastic “bow and arrow” mechanism. See our paper in Nature.

Also, we have found that high power, ballistic tongues have evolved at least three times independently among the lungless salamanders. We are working to determine the physiological and biomechanical basis for this remarkable performance. In addition, we are examining ballistic tongues of frogs and chameleons, which have evolved elastically powered tongues independently from those of salamanders and have different mechanisms. A central technique we use is capturing movements in slow motion to reveal details of their dynamics. See amphibians and reptiles feeding in slow motion on our Youtube playlist.

Spring-Loaded Tongues Launching when Cold

Chameleons, toads, and some salamanders can project their tongues ballistically using elastic recoil, like shooting a bow and arrow. Collagen connective tissue, like our tendons, can get stretched when the muscles contract, storing elastic energy. This energy can be released extremely quickly, far faster than the muscles contracted while stretching the connective tissue, which means that the tongue can be launched with a higher acceleration and power than if it were powered directly by muscle contraction. The rapid recoil of the collagen is decoupled temporally from the contraction of the muscle fibers that stretched it, so the rate at which the muscle stretches the collagen is irrelevant to the speed of tongue projection. When chameleons, toads, salamanders and other ectotherms cool down, the speed of muscle contraction slows and so do their movements. Ballistic movements such as tongue projection that make use of elastic recoil, however, are able to circumvent this thermal handicap, because the rate of recoil of collagen is independent of temperature.

This movie shows a Chamaeleo calyptratus, the veiled chameleon, capturing a suspended cricket at two different temperatures, 35°C (top) and 15°C (bottom), slowed down 100 times. You can see that tongue projection is similar at these two temperatures, but tongue retraction is much slower at the colder temperature. Tongue retraction does not use elastic recoil and depends upon direct muscle contraction. See our paper in Proceedings of the National Academy of Sciences.

Here a southern toad, Bufo terristris, capture crickets at two temperatures, 24°C (top) and 17°C (bottom), slowed down 100 times. Notice that ballistic mouth opening and tongue projection—which are elastically powered—are nearly identical, but that tongue retraction and mouth closing are slower in the cold. Like the chameleon above, the toad is able to circumvent the slowing effects of cold on muscle contraction using elastic recoil. See our paper in the Journal of Experimental Biology.

Like the toad and chameleon, the ballistic-tongued Hydromantes platycephalus can shoot its tongue at cold temperatures. This species lives at high elevation (~3000 m) in the Sierra Nevada mountains of California and is active at freezing temperatures, so a cold-proof tongue projection mechanism is an asset. This movie shows an individual feeding at two temperatures. See our paper in the Journal of Experimental Zoology.

Our research on thermal robustness of elastically powered movements was supported by the US National Science Foundation under Grants No. IOS 0842626 and 1350929. For information about access to data gathered as part of this research, please see our publications or contact ...

Functional Integration in Animal Locomotion

Collaborative research we are engaged in focuses on how locomotor forces are generated in the limbs and trunk during running, and how this has changed in tetrapod evolution. Because the trunk muscles have both locomotor and postural roles, as well as respiratory functions in amniotes, conflicts can arise during locomotion. We are investigating how locomotor-ventilatory conflicts and locomotor-postural conflicts have been resolved in vertebrate evolution. We record changes in muscle activity as we manipulate locomotor forces by altering the environment or introducing challenges to dogs, lizards, and salamanders as they locomote. See our publications in this area.

Feeding in Miniaturized Aquatic Organisms

Our work on feeding in tiny tadpoles demonstrates the influence of body size on the biomechanical options available to aquatic organisms. As aquatic animals become very small they must adopt different biomechanics to feed and locomote. Tadpoles of the frog genus Hymenochirus became smaller through evolution and abandoned the ancestral mode of suspension feeding to become suction-feeding predators on relatively large prey. In the process they converged in function to a remarkable degree with teleost fishes. See our paper in Nature.

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