Meeting Abstract
104.5 Sunday, Jan. 6 Phenotype manipulations confirm the role of pectoral muscles in avian thermogenic capacity PETIT, M.*; VEZINA, F.; Université du Québec à Rimouski, Groupe de recherche sur les environnements nordiques BOREAS, Centre for Northern Studies, Québec Centre for Biodiversity Science; Université du Québec à Rimouski, Groupe de recherche sur les environnements nordiques BOREAS, Centre for Northern Studies, Québec Centre for Biodiversity Science Magali.Petit@uqar.qc.ca
In winter, resident bird living at northern latitudes exhibit changes in body composition and metabolic performance in response to cold. Whole body mass, digestive organs and muscles mass as well as basal metabolic rate (BMR, reflecting minimal maintenance energy costs) and maximal thermogenic capacity (MSUM, a measure of cold tolerance) have been shown to be higher in winter relative to other seasons. Because birds undergoing cold stress produce heat by shivering, correlational studies suggested that MSUM directly depends on pectoral muscle size. However, this relationship has yet to be experimentally demonstrated. To investigate the relationship between pectoral muscle size and MSUM, we manipulated pectoral muscle size in free-living wintering black-capped chickadees (Poecile atricapillus). We removed half of the flight feathers of experimental individuals and compared their muscle morphology and metabolism with control birds captured over the same period. Results show that 1) “clipped” chickadees (n=12) had similar body mass (+1.8%), fat reserves (-13.4%), hematocrit level (+2.0%), BMR (+5.8%) and MSUM (+8.2%) but expressed larger pectoral muscles (+17.0%) than “controls” birds (n=15) and 2) that mass-independent MSUM varied with muscle score and was positively related to hematocrit. Birds showing the highest muscle scores had in average a MSUM +20.4% higher than birds with the smallest scores. These findings therefore support previously observed correlations. Large pectoral muscles are indeed associated with a better mass-independent thermogenic capacity in small resident birds.
