Histochemical Characterization and Distribution of Fiber Types in the Pectoralis Muscle of the Ostrich (Struthio camelus) and Emu (Dromaius novaehollandiae)

Abstract

The muscle fibers of the pectoralis (M. pectoralis pars thoracicus) of a male and a female ostrich (Struthio camelus) and a male and a female emu (Dromaius novaehollandiae) were studied histochemically for succinate dehydrogenase and myofibrillar adenosine triphosphatase. Slow‐tonic (ST), fast‐twitch oxidative‐glycolytic (FOG) and fast‐twitch glycolytic (FG) fibers were approximately equal in number and distribution in the emu pectoralis examined. In the ostriches, both predominantly FG and approximately equal areas, were present. ST fibers were significantly (P ≤ 0.05) larger than the similarly (P ≥ 0.05) sized FG and FOG fibers in the female ostrich and emus. In the male ostrich ST fibers were smaller (P ≤ 0.05) than FG fibers, neither of which were significantly (P ≥ 0.05) different from FOG fibers. The ratites have the greatest percentage and widest distribution of ST fibers found in any avian pectoralis studied to date. This could represent the ancestoral avian pectoralis, neoteny or an effect of flightlessness. ST fibers are used in the maintenance of posture, which is probably the main role of the pectoralis in the emu. The predominantly FG areas of the ostrich are indicative of an additional function, namely, behavioural display. Sexual dimorphism in the ostrich pectoralis is strongly suggested.

Osteology and myology of the wing of the Emu (Dromaius novaehollandiae), and its bearing on the evolution of vestigial structures

“…The wing of the Emu has no reported function, either anecdotal or hypothesized. An examination of the histology of M. pectoralis major, the muscle responsible for the downstroke in volant birds, revealed a high percentage of slow tonic fibers (those muscle fibers responsible for maintaining posture, but not contributing to activity), suggesting that the wing is normally held motionless (Rosser and George, 1985).…”

“…M. deltoideus major, M. subcoracoideus, M. biceps brachii). As this variability is also present in the wing of the kiwi and a function has not been reported for either structure (Rosser and George, 1985), it would be tempting to suggest that this widespread myological variability is due to a lack of function. In theory, this lack of function would weaken the strong selection normally exerted on wing morphology, leading to the accumulation of variation.…”

Histochemical and Morphometrical Characterization and Distribution of Fibre Types in Four Muscles of Ostrich (Struthio camelus)

“…The slow fibres are present by as much as 39% in the pectoralis muscle of the ratitis (Rosser and George, 1985) and they are certainly correlated to the inability of these birds to fly.…”

Muscle fiber type and metabolic profiles of four muscles from the African black ostrich

“…It is not yet known how many MHC isoforms the muscles of the ostrich express as no information could be found about the gene sequence of the MHC isoforms. Previously, Velotto and Crasto (2004) and Rosser and George (1985) used conventional ATPase staining (preincubation at pH 4.6 or pH 10.4) in conjunction with SDH staining (the latter being semi-quantitative) that allow for fibers to be classified as SO, FOG and FG. According to this classification system, Velotto and Crasto (2004) only found FG fibers in the m. gastrocnemius pars externa, and none in the m. tibialis cranialis caput tibiale, m. tibialis cranialis caput femorale and FL. The present study was able to identify only two muscle fiber types using an avian and mammalian fast MHC isoform antibody, whereas approximately 10 other antibodies failed to bind (data not shown).…”