Meeting Abstract
Avian wingbeat frequencies range from 2-80 Hz, resulting in differences in the contraction rate and shortening velocity of the flight muscles across species. Differential expression of myosin heavy chain (MHC) isoforms among muscles correlates with variation in maximum shortening velocity in both mammalian and avian muscle fibers. Thus, we expected MHC isoform complement in the pectoralis would vary across species in relation to the diversity of mechanical performance during flight. However, studies using SDS-PAGE electrophoresis have shown the adult fast isoform of the myosin heavy chain (MHC) to be the predominant, and often only, MHC isoform in the pectoralis of several avian species that differ in histological fiber type and wingbeat frequency. This finding lead us to previously hypothesize that the adult fast MHC isoform is essential to meet the mechanical demands of powered avian flight, with expression of this isoform in the pectoralis broadly conserved across species. To test this hypothesis, we examined the MHC expression across a greater diversity of avian species with a wide range of body size. MHC isoforms of the superficial pectoralis of 18 species collected in collaboration with the Fatal Light Awareness Program were separated and identified using SDS-PAGE electrophoresis and western blots. We find much greater interspecific diversity in MHC isoforms present in the avian pectoralis than previously observed, counter to our original hypothesis. The adult fast isoform is absent in some species, while a novel fast isoform previously not described in domestic chicken muscle is present in others. Further work is underway to examine whether the observed diversity of avian pectoral MHC expression may correlate with histological fiber type, phylogeny, or other physiological/behavioral factors influencing muscle function.
