BAIER, D.B.*; GATESY, S.: The Role Of Avian Slow-Twitch Fibers in Turkey Tail Display

EMGs from the tail muscles of male turkeys (Meleagris gallopavo) vary in amplitude between flight and display. In flight, caudal tail muscles yield high amplitude EMGs typical of twitch fibers. In display, male turkeys fan, raise, and turn their tails with little or no EMG activity. Slow-tonic muscle fibers (type III) like those found in the avian M. latissimus dorsi cranialis were hypothesized to be responsible for display postures, which can be maintained for several hours. Such tonic fibers do not propagate action potentials thereby explaining lack of conspicuous EMG signals. Histochemical staining for mATPase was used to characterize tail muscle fiber types. The primary muscles involved in raising the tail (M. levator caudae pars vertebralis, M. levator caudae pars rectricalis) and in fanning (M. bulbi rectricium) all show mixed populations of slow-twitch (type I) and fast-twitch (type II) fibers. The muscle previously assumed to turn the tail (M. lateralis caudae) contains only fast-twitch (type II) fibers. No slow-tonic (type III) fibers have been identified in any caudal muscle. However, avian slow-twitch fibers are also multiply innervated, unlike mammalian slow-twitch fibers. Despite their innervation, avian slow-twitch fibers are often considered to be action potential-propogating. Our histochemical results, together with EMG activities, suggest that avian slow-twitch fibers are responsible for maintaing tail posture during display.