Histochemistry of flight muscles in the Jamaican fruit bat, Artibeus jamaicensis: implications for motor control

Flight style of the black-billed magpie: variation in wing kinematics, neuromuscular control, and muscle composition

Black-billed magpies (Pica pica; Corvidae) exhibit an unusual flight style with pronounced, cyclic variation in wingbeat frequency and amplitude during level, cruising flight. In an effort to better understand the underlying internal mechanisms associated with this flight style, we studied muscle activity patterns, fiber composition of the pectoralis muscle, and wingbeat kinematics using both laboratory and field techniques. Over a wide range of speeds in a windtunnel (0-13.4 m s-1), wingbeat frequency, wingtip elevation, and relative intensity of electromyographic (EMG) signals s-1 from the flight muscles were least at intermediate speeds, and increased at both slower and faster speeds, in approximate agreement with theoretical models that predict a U-shaped curve of power output with flight speed. Considerable variation was evident in kinematic and electromyographic variables, but variation was continuous, and, thus, was not adequately described by the simple two-gait system which is currently accepted as describing gait selection during vertebrate flight. Indirect evidence suggests that magpies vary their flight style consistent with reducing average power costs in comparison to costs associated with continuous flapping at a fixed level of power per wingbeat. The range of variation for the kinematic variables was similar in the field and lab; however, in the field, proportionally fewer flights showed significant correlations between wingbeat frequency and the other variables. Average flight speed in the field was 8.0 m s-1. Average wingbeat frequency was less in the field than in the windtunnel, but mean values for wingtip elevation and wingspan at midupstroke were not significantly different. Histological study revealed that the pectoralis muscle of magpies contained only fast-twitch (acid-stable) muscle fibers, which were classified as red (R) and intermediate (I) based on oxidative and glycolytic capacities along with fiber diameter. This fiber composition may be related to variation in wingbeat kinematics, but such composition is found in the pectoralis of other bird species. This suggests that the muscle fibers commonly found in the pectoralis of small to medium sized birds are capable of a wider range of efficient contractile velocities than predicted by existing theory. Future studies should explore alternative explanations for variation in wingbeat kinematics, including the potential role of nonverbal communication among cospecifics.

Histochemical and myosin composition of vampire bat (Desmodus rotundus) pectoralis muscle targets a unique locomotory niche

The vampire bat pectoralis muscle contains at least four fiber types distributed in a nonhomogeneous pattern. One of these fiber types, here termed IIe, can be elucidated only by adenosine triphosphatase (ATPase) histochemistry combined with reactions against antifast and antislow myosin antibodies. The histochemical and immunohistochemical observations indicate a well-developed specialization of function within specific regions of the muscle. In parallel, analyses of native myosin isoforms and myosin heavy chain isoforms indicate two points. First, the histochemical "type IIe" fiber is predominant in cranial portions of the muscle, and myosin extracted from these regions exhibits a unique electrophoretic mobility not observed in the myosin isoforms of more traditional laboratory mammals. Second, the type I fibers are confined to the pectoralis abdominalis muscle and a small adjacent region of the caudal part of the pectoralis. This pattern of type I fiber distribution is considered a derived character state compared to muscle histochemical phenotype and isoform composition in the pectoralis muscles of other phyllostomids we have studied (Artibeus jamaicensis, Artibeus lituratus, Carollia perspicillata). We relate this to the unique locomotory needs of the common vampire bat, Desmodus rotundus.