title: Fluctuations in oxygen influence facultative endothermy in bumblebees.
abstract: Bumblebees are facultative endotherms, having the ability to elevate thorax temperature above ambient temperature by elevating metabolism. Here, we investigated the influence of hypoxia on metabolic demands and thermoregulatory capabilities of the bumblebee Bombus terrestris. We measured thorax temperature, rates of oxygen consumption and carbon dioxide production, and abdominal pumping rates of bees randomly exposed to oxygen levels of 20, 15, 10 and 5 kPa at 26°C. Under normoxia, bumblebees maintained an elevated mean thorax temperature of 35.5°C. There was no significant change in thorax temperature at 15 kPa O2 (33.4°C). Mean thorax temperature decreased significantly at 10 kPa O2 (31.6°C) and 5 kPa O2 (27.3°C). Bees were able to maintain an elevated metabolic rate at 15 and 10 kPa O2. In normoxia, endothermic bees exhibited periods of rapid abdominal pumping (327 min(-1)) interspaced by periods of no abdominal pumping. At 10 kPa O2, abdominal pumping rate decreased (255 min(-1)) but became more continuous. Upon exposure to 5 kPa, metabolic rate and abdominal pumping rate (152 min(-1)) decreased, although the animals continued abdominal pumping at the reduced rate throughout the exposure period. Bumblebees are able to meet the energetic demands of endothermy at 15 kPa O2, but become compromised at levels of 10 kPa O2 and below.
authors.affiliation: Developmental Integrative Biology Cluster, Department of Biological Sciences, University of North Texas, Denton, TX 76203, USA edzial@unt.edu.
authors.forename: Edward M
authors.initials: EM
authors.lastname: Dzialowski
authors.affiliation: Department of Biological Sciences, Brock University, St Catharines, ON, Canada, L2S 3A1.
authors.forename: Glenn J
authors.initials: GJ
authors.lastname: Tattersall
authors.affiliation: School of Biological Sciences, University of Tasmania, Hobart, TAS 7005, Australia.
authors.forename: Stewart C
authors.initials: SC
authors.lastname: Nicol
authors.affiliation: Institute of Marine and Antarctic Studies, University of Tasmania, Hobart, TAS 7005, Australia.
authors.forename: Peter B
authors.initials: PB
authors.lastname: Frappell
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001516:Bees / Q000502:physiology*; D001831:Body Temperature; D001833:Body Temperature Regulation / Q000502:physiology*; D002245:Carbon Dioxide / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004734:Energy Metabolism / Q000502:physiology*; D008954:Models, Biological; D010100:Oxygen / Q000378:metabolism / Q000494:pharmacology; D010101:Oxygen Consumption / Q000502:physiology
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen
keywords: Bombus terrestris; Hypoxia; Metabolism; Thermoregulation; Ventilation