Environmental temperature has profound effects on the physiological processes of animals whose body temperature is determined by their surroundings, such as reptiles and amphibians. The ability of such animals to be active at low temperatures is limited by the slowing of physiological processes such as the speed of muscle contraction. The explosive movements of ballistic tongue projection in salamanders and chameleons are unusual in maintaining extremely high performance across a broad range of temperatures. This study will examine the physiological and biomechanical processes that confer this high performance and temperature insensitivity. Tongue projection is powered by rapid elastic recoil of collagen tendon-like structures (in a "bow and arrow" mechanism) which frees the dynamics of the movement from the dynamics of muscle contraction. This mechanism may endow this system and other musculoskeletal systems with an expanded thermal breadth of high performance, because the elastic recoil of collagen has a much lower temperature sensitivity than muscle contraction speed and power. This study will use high-speed digital imaging and recordings of muscle activation patterns during tongue projection, and measurements of the speed and power of muscle contractions, each at a range of temperatures. The combined data will enable a robust test of this elastic recoil model, and data from two independently evolved systems -salamanders and chameleons - will permit a test of the model's generality and predictive power. The results will further our understanding of the complex interplay of environment, biomechanics and physiology, which cannot be confidently predicted from first principles. Results will also provide testable predictions about the thermal responses of diverse biological systems with elastic components. Tongue projection is a highly engaging and effective vehicle for communicating discoveries in physiology and biomechanics, and is ideal for recruiting and training students in all aspects of scientific research. The results may also have practical applications in the design of prosthetic devices and sports equipment that improve performance and the functional range of muscles.
