Fattening Physiology in a Long-Distance Migrant: Interplay between Baseline Corticosterone, Diet, and the Endocannabinoidome.

AbstractMigration and subsequent reproduction are the most demanding stages in the life cycle of migratory birds, especially for capital breeders. Fattening rate is a key parameter determining the energy available to meet these high energy demands. For five consecutive years, we measured physiological parameters (body condition, baseline corticosterone, diet, endocannabinoidome lipids) involved in energy regulation in female greater snow geese. Goose body condition increased during spring fattening period until reaching a plateau a few days before migratory departure. Baseline corticosterone followed a similar pattern with an initial increase followed by a slight decrease at the end of spring staging. Individuals with high baseline corticosterone also had a high proportion of corn in their diet. The endocannabinoids N-arachidonoylethanolamine (AEA) and 2-arachidonoylglycerol (2-AG), known to play central roles in energy homeostasis, appetite, and fat storage, were detected in plasma but showed no association with diet or body condition. Other endocannabinoidome lipids, like N-oleoylethanolamine (OEA) and N-palmitoylethanolamine (PEA), were negatively associated with dietary corn intake, suggesting a potential role in regulating feeding behavior. The endocannabinoids 2-oleoyl-glycerol (2-OG) and 2-palmitoyl-glycerol (2-PG) were negatively associated with body condition, as was the essential fatty acid linoleic acid (LA); all declined sharply once individuals reached their final body condition. This suggests a downregulation of foraging activity and a shift in lipid metabolism from energy accumulation to maintenance at the end of the premigratory stage. Our results suggest complementary roles of the hormonal and lipidic mediators during the fattening process in preparation for migration. The lipidomic results, though exploratory, provide novel directions for future research.