Muscle fiber types in a migratory and a non-magratory avian species.

Abstract

Most vertebrate skeletal muscles are composed of mixed populations of fibers that differ in their biochemical and contractile properties. Three fiber types can be distinguished by standard histochemical staining techniques: B-red fibers, which are rich in mitochondrial enzymes and have an acid-stable myosin ATPase; a-white fibers, which are poor in mitochondrial enzymes and have acid labile myosin ATPase; and a-red fibers, which are "intermediate" between the other two types. In this study of bird muscle, one running/walking muscle (tibialis anterior) and one flight muscle (pectoralis) were studied in the migratory mourning dove and the non-migratory northern bobwhite. The muscles were fiber-typed and the mean size of each fiber type (in ~m2) and the percentage of muscle occupied by each fiber type determined. Superficial (outermost 3 mm) and deep samples were taken from the pectoralis. The tibialis anterior was sampled through its entire cross section. B-red fibers were not found in the pectoralis of either species. Deep dove pectoralis is predominantly a-red (68.3%). Superficial dove pectoralis is predominantly a-white (72.5%). The bobwhite pectoralis is predominantly a-white with a uniform scattering of a-red fibers and no statistical difference between superficial and deep regions. The bobwhite tibialis anterior has all three fiber types, including highly oxidative B-red fibers. The dove tibialis anterior is predominantly a-white. The fiber composition of the pectoralis muscles of these two species reflects the pattern of usage of the muscles. The non-migratory bobwhite, which uses its pectoralis muscle only for short bursts of flight, contains mostly low-endurance a-white fibers. The pectoralis muscle of the dove, which is utilized during moderately long seasonal migrations, contains mostly higher endurance a-red fibers. The fiber composition of the tibialis anterior muscle also reflects the pattern of usage in these two species. The tibialis anterior of the bobwhite (which would "rather run than fly") contains high endurance a-red and B-red fibers in addition to a-white fibers. The tibialis anterior of the dove, which contributes little to the seasonal migration of this species, contains predominantly a-white fibers.