MOON, Brad; Univ. of Louisiana, Lafayette: Muscle Function and the Evolution of the Rattlesnake Rattling System

Rattling by rattlesnakes is one of the fastest vertebrate movements and involves some of the highest contraction frequencies sustained by vertebrate muscle. The high performance tailshaker muscles of rattlesnakes can sustain contraction frequencies up to 100 Hz for minutes to hours. Comparisons of the anatomical and physiological properties of tail muscles among rattlesnakes and their relatives can be used to study the evolution of high performance muscles and of the rattle. Rattlesnake tail muscles have a very high aerobic capacity. Closely related pitvipers such as copperheads vibrate their tails defensively and have tail muscles with an intermediate aerobic capacity. More distant relatives such as colubrid snakes have tail muscles that are not physiologically specialized, whether they vibrate their tails defensively or not. Similarly, tail vibration frequencies are highest in rattlesnakes, intermediate in copperheads, and lowest in colubrids. These results indicate that defensive tail vibration and high performance tail muscles evolved gradually, before the rattle evolved.