title: Seasonal variation of metabolic thermogenesis in Eurasian tree sparrows (Passer montanus) over a latitudinal gradient.
abstract: Phenotypic flexibility of various morphological and physiological characters is widespread in animals. Resident endothermic animals of temperate climates provide a natural experiment in phenotypic flexibility. In this study, we took an integrative approach to assess seasonal and geographic influences on metabolism in Eurasian tree sparrows (Passer montanus). We measured resting metabolic rate (RMR), masses of internal organs, mitochondrial respiration capacities in liver and muscle, cytochrome C oxidase (COX) activities in liver and muscle, and circulating levels of plasma triiodothyronine (T3) and thyroxine (T4) in summer and winter sparrows at two sites from southeastern (Wenzhou) and northeastern (Qiqihar) China that differ in climate. Body masses of tree sparrows were significantly higher in winter than in summer at both sites but did not differ with latitude. RMRs of tree sparrows varied significantly with both latitude and season, with RMRs of Qiqihar birds being higher than those of Wenzhou birds and with RMRs being higher in winter than in summer. Consistently, dry masses of brain, lung, liver, gizzard, small intestine, rectum, and total digestive tract varied significantly with either latitude or season. State 4 respiration and COX activity in liver and muscle were remarkably higher in Qiqihar and increased significantly in winter. Circulating levels of plasma T3 also showed significant seasonal and latitudinal variation and was higher in Qiqihar in winter than in other groups. These data suggest that tree sparrows mainly coped with cold by enhancing thermogenic capacities through heightened activity of respiratory enzymes and higher levels of plasma thyroid hormones (T3). These results are consistent with a pronounced seasonal and latitudinal phenotypic flexibility mediated through physiological and biochemical adjustments in Eurasian tree sparrows.
authors.affiliation: School of Life and Environmental Sciences, Wenzhou University, Wenzhou 325035, China; Key Laboratory for Water Environment and Marine Biological Resources Protection in Zhejiang Province, Wenzhou 325035, China; and Institute of Applied Ecology, Wenzhou University, Wenzhou 325035, China; 2Department of Biology, Daqing Normal College, Daqing 163712, China; 3College of Life Science and Engineering, Qiqihar University, Qiqihar 161006, China.
authors.forename: Wei-Hong
authors.initials: WH
authors.lastname: Zheng
authors.forename: Ming
authors.initials: M
authors.lastname: Li
authors.forename: Jin-Song
authors.initials: JS
authors.lastname: Liu
authors.forename: Shu-Li
authors.initials: SL
authors.lastname: Shao
authors.forename: Xing-Jun
authors.initials: XJ
authors.lastname: Xu
mesh_terms: D000818:Animals; D001481:Basal Metabolism; D002681:China; D002980:Climate; D009929:Organ Size; D010641:Phenotype; D012621:Seasons; D046370:Sparrows / Q000502:physiology*; D022722:Thermogenesis; D013963:Thyroid Hormones / Q000097:blood*
chemical_list: D013963:Thyroid Hormones