Data from: Altered expression of pectoral myosin heavy chain isoforms corresponds to migration status in the white-crowned sparrow (Zonotrichia leucophrys gambelii)

Birds undergo numerous changes as they transition across life history stages, yet relatively few studies have examined how birds adapt to the dynamic mechanical demands associated with such transitions. Myosin heavy chain (MHC) expression, often linked with muscle fiber type, is strongly correlated with a muscle’s mechanical power generating capability. We examined pectoral fiber type and MHC expression in a long-distance migrant, the white-crowned sparrow (Zonotrichia leucophrys gambelii), using histological methods and SDS-PAGE electrophoresis as they progressed from wintering through spring departure and arrival at the breeding grounds. Although no difference in histological fiber type was observed, MHC expression varied significantly over the course of the study. Wintering birds expressed a single, newly classified adult fast 2 isoform. At spring departure, pectoral isoform expression included two MHC isoforms: the adult fast 2 isoform along with a smaller proportion of a newly present adult fast 1 isoform. By spring arrival, both adult fast isoforms present at departure remained, yet expression had shifted to a greater relative proportion of the adult fast 1 isoform. Altering pectoral MHC isoform expression in preparation for and during spring migration may represent an adaptation to modulate muscle mechanical output to support long-distance flight.