Meeting Abstract
Glucocorticoids (GC) are associated with responses to stress and also energy metabolism, tissue remodeling and homeostasis. At low circulating levels GC bind high-affinity mineralocorticoid receptors (MR) and affect anabolic pathways including tissue repair and homeostasis. At elevated levels, they bind to GC receptors (GR) activating catabolic pathways. Avian migrants express phenotypic flexibility by seasonally modifying anatomy, physiology and behavior to accommodate energetic demands of each stage. We hypothesized that GC signaling may contribute to the phenotypic flexibility in the pectoralis (flight) and gastrocnemius (leg) muscles in sparrows on the wintering grounds at three distinct stages leading up to migratory departure in spring: winter, pre-nuptial molt, and pre-departure. CORT was detected in plasma and in both muscles but CORT signaling differed across muscles and stages. Both plasma and pectoralis CORT were elevated at pre-departure (p<0.05). Expression of 1lβ-hydroxysteroid dehydrogenase (1lβ-HSD) Type 2 (inactivates CORT) increased in the pectoralis at pre-departure (p<0.05), whereas, 1lβ-HSD Type 1 (regenerates CORT) did not change. Neither isoform was detected in the gastrocnemius. Expression of MR only was elevated in pectoralis at pre-departure (p<0.05). These data suggest that anabolic functions predominate in the pectoralis only while catabolic activity is undetected in either muscle at pre-departure. Thus, we find evidence for potential pathways by which GC signaling may function to regulate the phenotypic flexibility expressed by birds anticipating migratory departure.
