CAPILLARITY AND FIBER TYPES IN LOCOMOTORY MUSCLES OF WILD COMMON COOTS, FULICA-ATRA

Six locomotory muscles of wild common coots, Fulica atl-a, were analyz ed histochemically. Capillarity and fiber-type distributions were corr elated to the functional implications and physiological needs of each muscle. Leg muscles exhibit three unevenly distributed fiber types, a pattern that reflects the great variety of terrestrial and aquatic loc omotory performances that coots are able to develop. Aerobic zones are presumably recruited during steady swimming and diving, while regions with anaerobic characteristics may be used for bursts of activity suc h as sprint swimming or during take off, when coots run along the wate r's surface, Fiber types and capillarization in wing muscles have a ma rked oxidative trend. High wing beat frequencies, short and broad wing s, and the long distance migrations that these birds perform indicate that the presence of high numbers of oxidative fibers and the well dev eloped capillary supply are needed for enhanced oxygen uptake. The pec toralis muscle, except in its deep part, has exclusively fast oxidativ e fibers with a very high staining intensity for succinate dehydrogena se assay as compared to the same fiber type of other muscles. Its pred ominant role in flapping flight justifies these characteristics that a re typical of fibers with high aerobic metabolism. The deep part of th e pectoralis muscle presents a low proportion of an unusual slow anaer obic fiber type. These fibers could play a role during feeding dives w hen the bird presses the air out of the feathers by tightening the win gs against the body. A linear relationship between capillary and fiber densities in all coot muscles studied reflects an adjustment between fiber diameter and vascularization in order to obtain the oxygen for m itochondrial supply. This strategy seems a suitable way to cope with t he rigid aerobic constraints that flying and diving impose upon the co ot's physiology. J. Morphol. 237:147-164, 1998. (C) 1998 Wiley-Liss, I nc.