Reference number: OPUSeJ 201302062236FRS
Links: to published article: http://www.ncbi.nlm.nih.gov/pubmed/23255194
to pre-reviewed version: N/A
Title: Real-time measurement of metabolic rate during freezing and thawing of the wood frog, Rana sylvatica: implications for overwinter energy use
Authors: Brent J. Sinclair 1,*, Joseph R. Stinziano 1, Caroline M. Williams 1, Heath A. MacMillan 1, Katie E. Marshall 1, and Kenneth B. Storey 2
Abstract: Ectotherms overwintering in temperate ecosystems must survive low temperatures while conserving energy to fuel post-winter reproduction. Freeze-tolerant wood frogs, Rana sylvatica, have an active response to the initiation of ice formation that includes mobilising glucose from glycogen and circulating it around the body to act as a cryoprotectant. We used flow-through respirometry to measure CO(2) production ( ) in real time during cooling, freezing and thawing. CO(2) production increases sharply at three points during freeze-thaw: at +1°C during cooling prior to ice formation (total of 104±17 μl CO(2) frog(-1) event(-1)), at the initiation of freezing (565±85 μl CO(2) frog(-1) freezing event(-1)) and after the frog has thawed (564±75 μ l CO(2) frog(-1) freezing event(-1)). We interpret these increases in metabolic rate to represent the energetic costs of preparation for freezing, the response to freezing and the re-establishment of homeostasis and repair of damage after thawing, respectively. We assumed that frogs metabolise lipid when unfrozen and that carbohydrate fuels metabolism during cooling, freezing and thawing, and when frozen. We then used microclimate temperature data to predict overwinter energetics of wood frogs. Based on the freezing and melting points we measured, frogs in the field were predicted to experience as many as 23 freeze-thaw cycles in the winter of our microclimate recordings. Overwinter carbohydrate consumption appears to be driven by the frequency of freeze-thaw events, and changes in overwinter climate that affect the frequency of freeze-thaw will influence carbohydrate consumption, but changes that affect mean temperatures and the frequency of winter warm spells will modify lipid consumption.
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1 Department of Biology, University of Western Ontario, London, ON N6A 5B7, Canada *Author for correspondence (email@example.com)
2 Institute of Biochemistry, Carleton University, Ottawa, ON K1S 5B6, Canada
Thanks to Jan Storey and two anonymous referees for insightful comments on an earlier version of the manuscript.
This research was supported by a Natural Sciences and Engineering Research Council of Canada (NSERC) Undergraduate Research Award to J.R.S.; an NSERC Discovery Grant, the Canadian Foundation for Innovation and an Ontario Early Researcher Award to B.J.S.; an Ontario Graduate Scholarship to C.M.W.; NSERC doctoral scholarships to K.E.M. and H.A.M.; and an NSERC Discovery grant and Canada Research Chair to K.B.S.
Subject: Science/ overwinter metabolism
Bibliography: see Forum
Citation: Sinclair BJ et al, 2013, “Real-time measurement of metabolic rate during freezing and thawing of the wood frog, Rana sylvatica: implications for overwinter energy use”, J Exp Biol. 2013 Jan 15;216(Pt 2):292-302. doi: 10.1242/jeb.076331. http://www.ncbi.nlm.nih.gov/pubmed/23255194