Meeting Abstract
Plethodontid salamanders have evolved high-performance, ballistic tongue projection. Examples of extreme performance abound: Hydromantes can shoot its tongue from the body by 80% of SVL, Thorius can accelerate its tongue at 600 G, and Bolitoglossa can amplify muscle power 100 times with the use of collagen springs. Ballistic projection, in which the tongue skeleton leaves the body entirely, has evolved multiple times independently in plethodontids, and in each case is accomplished by an elastic-recoil mechanism that both amplifies muscle power and circumvents thermal constraints on muscle contraction, allowing projection at cold temperatures (as low as 2°C in Hydromantes). The bow-and-arrow mechanism of tongue projection has evolved via relatively minor changes in the morphology of the subarcualis rectus muscle (SAR), in which myofiber connections to the tongue skeleton are lost and collagen aponeuroses within the SAR are elaborated to form spiral sheets that act as springs to store muscle energy and release it quickly as mechanical work. Motor control has evolved by a simple shift in the timing of muscle activity that allows the collagen to be stretched prior to tongue projection. Muscle contractile experiments show that muscle contractile physiology is conserved evolutionarily. These findings in salamanders, together with data from chameleons and frogs, reveal that relatively minor changes in morphology and motor control can dramatically increase the performance and thermal robustness of animal movements.
