CAPILLARITY AND FIBER TYPES IN LOCOMOTORY MUSCLES OF WILD MALLARD DUCKS (ANAS-PLATYRHYNCHOS)

Six locomotory muscles from wild mallard ducks (Anas platyrhynchos) we re analysed by histochemical methods. Special care was taken in sample procedure in order to describe the heterogeneity found throughout eac h muscle. Capillarity and fibre-type distributions were correlated to the functional implications and physiological needs of each muscle. Co mparisons between our results and similar previous reports on dabbling and diving ducks are also discussed. Muscles from the leg presented t he most heterogeneous fibre-type distributions, which are correlated t o the wide range of terrestrial and aquatic locomotory performances sh own by these animals. More specialized muscles such as pectoralis. use d almost exclusively for flapping flight, had more homogeneous fibre-t ype distributions, whereas muscles from the wing presented a high prop ortion of glycolytic fibres probably recruited during non-steady flapp ing flight. Deep muscle pectoralis zones and parts of the gastrocnemiu s which are closer to the bone are remarkable for their high capillari ty indices and oxidative capacities, which suggests that these parts a re recruited during sustained flapping flight and swimming. However, t wo different strategies for achieving these high oxygen needs are evid ent, indicating that the fibre cross-sectional area plays an important role in the modulation of the oxygen supply to the muscle cells.