From doubly labelled water to half‐life; validating radio‐isotopic rubidium turnover to measure metabolism in small vertebrates. Issue 7 (13th May 2013)

• Record Type: Journal Article
• Authors: Tomlinson, Sean; Maloney, Shane K.; Withers, Philip C.; Voigt, Christian C.; Cruz‐Neto, Ariovaldo P.; Bowen, Gabriel
• Is Part Of: Methods in ecology and evolution. Volume 4:Issue 7(2013:Jul.)
• Page Start: 619
• Page End: 628
• Publication Date: 2013-05-13
• Subjects: Ecology -- Periodicals; Evolution -- Periodicals; 577
• DOI: 10.1111/2041-210X.12056
• Languages: English
• ISSNs: 2041-210X

Abstract

<abstract abstract-type="main" id="mee312034-abs-0001"> <title>Summary</title> <p> <list id="mee312056-list-0001" list-type="order"> <list-item> <p>The doubly labelled water method (DLW) is widely used to measure field metabolic rate (FMR), but it has some limitations. Here, we validate an innovative technique for measuring FMR by comparing the turnover of isotopic rubidium (<sup>86</sup>Rb k<sub>b</sub>) with DLW depletion and the rate of CO<sub>2</sub> production (<inline-graphic mimetype="image" xlink:href="ark:/27927/pgg25t7djgf" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><mml:math altimg="urn:x-wiley:2041210X:media:mee312056:mee312056-math-0001" overflow="scroll" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mrow><mml:mover><mml:mrow><mml:mi>V</mml:mi></mml:mrow><mml:mo>·</mml:mo></mml:mover></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">co</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:msub></mml:mrow></mml:math>) measured by flow‐through respirometry (FTR) for two dunnart species (Marsupialia: Dasyuridae), <italic>Sminthopsis macroura</italic> (17 g) and <italic>Sminthopsis ooldea</italic> (10 g).</p> </list-item> <list-item> <p>The rate of metabolism as assessed by <inline-graphic mimetype="image" xlink:href="ark:/27927/pgg25t7djmn" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><mml:math altimg="urn:x-wiley:2041210X:media:mee312056:mee312056-math-0002" overflow="scroll" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mrow><mml:mover><mml:mrow><mml:mi>V</mml:mi></mml:mrow><mml:mo>·</mml:mo></mml:mover></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">co</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:msub></mml:mrow></mml:math> (FTR) and <sup>86</sup>Rb k<sub>b</sub> was significantly correlated for both species (<italic>S. macroura</italic>, <italic> r</italic><sup>2</sup> = 0·81, <italic>P</italic> = 1·19 × 10<sup>−5</sup>; <italic>S. ooldea</italic>, <italic> r</italic><sup>2</sup> = 0·63, <italic>P</italic> = 3·84 × 10<sup>−4</sup>), as was <inline-graphic mimetype="image" xlink:href="ark:/27927/pgg25t7djk3" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><mml:math altimg="urn:x-wiley:2041210X:media:mee312056:mee312056-math-0003" overflow="scroll" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mrow><mml:mover><mml:mrow><mml:mi>V</mml:mi></mml:mrow><mml:mo>·</mml:mo></mml:mover></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">co</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:msub></mml:mrow></mml:math> from FTR and DLW for <italic>S. macroura</italic> (<italic>r</italic><sup>2</sup> = 0·43, <italic>P</italic> = 0·039), but not for <italic>S. ooldea</italic> (<italic>r</italic><sup>2</sup> = 0·29, <italic>P</italic> = 0·168). There was no relationship between <inline-graphic mimetype="image" xlink:href="ark:/27927/pgg25t7djjj" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><mml:math altimg="urn:x-wiley:2041210X:media:mee312056:mee312056-math-0004" overflow="scroll" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mrow><mml:mover><mml:mrow><mml:mi>V</mml:mi></mml:mrow><mml:mo>·</mml:mo></mml:mover></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">co</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:msub></mml:mrow></mml:math> from DLW and <sup>86</sup>Rb k<sub>b</sub> for either species (<italic>S. macroura r</italic><sup>2</sup> = 0·22, <italic>P</italic> = 0·169; <italic>S. ooldea r</italic><sup>2</sup> = 0·21, <italic>P</italic> = 0·253). We conclude that <sup>86</sup>Rb k<sub>b</sub> provided useful estimates of metabolic rate for dunnarts.</p> </list-item> <list-item> <p>Meta‐analysis provided different linear relationships between <inline-graphic mimetype="image" xlink:href="ark:/27927/pgg25t7djh0" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><mml:math altimg="urn:x-wiley:2041210X:media:mee312056:mee312056-math-0005" overflow="scroll" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mrow><mml:mover><mml:mrow><mml:mi>V</mml:mi></mml:mrow><mml:mo>·</mml:mo></mml:mover></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">co</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:msub></mml:mrow></mml:math> and <sup>86</sup>Rb k<sub>b</sub> for endotherms and ectotherms, suggesting different proportionalities between metabolic rate and <sup>86</sup>Rb k<sub>b</sub> for different taxa. Understanding the mechanistic basis for this correlation might provide useful insights into the cause of these taxonomic differences in the proportionality. At present, it is essential that the relationship between metabolic rate and <sup>86</sup>Rb k<sub>b</sub> be validated for each taxon of interest.</p> </list-item> <list-item> <p>The advantages of the <sup>86</sup>Rb technique over DLW include lower equipment requirements and technical expertise, and the longer time span over which measurements can be made. The <sup>86</sup>Rb method might be particularly useful for estimating FMR of groups for which the assumptions of the DLW technique are compromised (e.g. amphibians, diving species and fossorial species), and groups that are practically challenging for DLW studies (e.g. insects).</p> </list-item> </list> </p> </abstract>