Recently we have discovered that high-power ballistic movements can maintain their high performance even when the muscles powering them are cold. Ectothermic animals whose body temperature is determined by the environment including salamanders, frogs, and chameleons use spring-loaded tongue projection that achieves high performance even at low body temperatures. They can perform ballistic tongue projection at muscle temperatures that are 20°C or more below the body temperature of an endothermic bird or a mammal. By storing muscle energy slowly in springy tendon-like tissue and subsequently releasing the energy quickly, these animals can circumvent the slowing of muscle contraction that occurs at low temperature. Our paper in Proceedings of the National Academy of Sciences documents this phenomenon in chameleons. See press coverage of this and other research.
High-Power Ballistic Movements
This photo 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. Also, we have found that high power, ballistic tongues have evolved at least three times independently among the lungless salamanders. We are currently working to determine the physiological and biomechanical basis for this remarkably high 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.
Limb-Trunk Integration in Running Tetrapods
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 use a technique in which the muscles act as force transducers: we record changes in muscle activity as we manipulate locomotor forces by altering the environment or applying perturbations to dogs, lizards, and salamanders as they locomote. We have several recent publications from this research on dogs and salamanders.
Feeding in Tiny Tadpoles
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.