Meeting Abstract
Migratory birds seasonally increase fat stores and the enzymatic capacity for fatty acid transport and catabolism to fuel long-distance migratory flights. However, catabolism of lean mass is also well documented in migratory birds and, if adaptive for migratory flight, seasonal changes in the capacity for protein metabolism should occur. To investigate seasonal changes in fuel storage and metabolism in preparation for migration, I conducted a photoperiod manipulation using captive White-throated Sparrows (Zonotrichia albicollis). I measured body composition and water-restricted metabolic rate through a “winter” photoperiod, and after exposing half the birds to a “spring” photoperiod. Lean mass peaked for all birds during the winter, but after photostimulation spring birds rapidly increased fat mass and the activity of fat catabolism enzymes while displaying peak Zugunruhe. There was a 25-fold increase in muscle sarcolipin transcript levels in spring birds, which may stimulate mitochondrial biogenesis and fat catabolism through sarco/endoplasmic reticulum Ca2+ ATPase (SERCA) uncoupling. Body composition remained stable in winter birds and metabolic rates did not differ significantly between seasons. However, spring birds lost more water for a given metabolic rate, driving greater rates of lean mass loss alongside altered protein catabolism enzyme activities. This suggests that protein may be catabolized at a greater rate during migratory seasons, potentially to cope with higher rates of water loss.
