title: Reaction norms in natural conditions: how does metabolic performance respond to weather variations in a small endotherm facing cold environments?
abstract: Reaction norms reflect an organisms' capacity to adjust its phenotype to the environment and allows for identifying trait values associated with physiological limits. However, reaction norms of physiological parameters are mostly unknown for endotherms living in natural conditions. Black-capped chickadees (Poecile atricapillus) increase their metabolic performance during winter acclimatization and are thus good model to measure reaction norms in the wild. We repeatedly measured basal (BMR) and summit (Msum) metabolism in chickadees to characterize, for the first time in a free-living endotherm, reaction norms of these parameters across the natural range of weather variation. BMR varied between individuals and was weakly and negatively related to minimal temperature. Msum varied with minimal temperature following a Z-shape curve, increasing linearly between 24°C and -10°C, and changed with absolute humidity following a U-shape relationship. These results suggest that thermal exchanges with the environment have minimal effects on maintenance costs, which may be individual-dependent, while thermogenic capacity is responding to body heat loss. Our results suggest also that BMR and Msum respond to different and likely independent constraints.
authors.affiliation: Département de Biologie, chimie et géographie, Université du Québec à Rimouski, 300 Allée des Ursulines, Rimouski (Québec), G5L 3A1, Canada; Groupe de recherche sur les environnements nordiques BOREAS, Rimouski (Québec), Canada; Centre d'Etudes Nordiques, Québec (Québec), Canada; Centre de la Science de la Biodiversité du Québec, Montréal (Québec), Canada.
authors.forename: Magali
authors.initials: M
authors.lastname: Petit
authors.affiliation: Département de Biologie, chimie et géographie, Université du Québec à Rimouski, 300 Allée des Ursulines, Rimouski (Québec), G5L 3A1, Canada; Groupe de recherche sur les environnements nordiques BOREAS, Rimouski (Québec), Canada; Centre d'Etudes Nordiques, Québec (Québec), Canada; Centre de la Science de la Biodiversité du Québec, Montréal (Québec), Canada.
authors.forename: François
authors.initials: F
authors.lastname: Vézina
mesh_terms: D000064:Acclimatization; D000818:Animals; D001481:Basal Metabolism; D003080:Cold Temperature; D004777:Environment; D005260:Female; D008297:Male; D046109:Passeriformes / Q000502:physiology*; D012621:Seasons; D014887:Weather