Validation of a non-invasive blood-sampling technique for doubly-labelled water experiments
- 20 March 2003
- journal article
- research article
- Published by Wiley in Journal of Experimental Zoology
- Vol. 296 (2) , 87-97
- https://doi.org/10.1002/jez.a.10121
Abstract
Two techniques for bleeding small mammals have been used in doubly‐labeled water (DLW) studies, including vena puncture and the use of starved nymphal stages of hematophagous reduviid bugs (Reduviidae, Hemiptera). In this study, we tested the validity of using reduviid bugs in doubly‐labeled water experiments. We found that the isotope enrichment in initial blood samples collected with bugs was significantly lower compared to isotope enrichment in blood samples obtained using vena puncture. We therefore used the desiccation method for estimating total body water (TBW) in DLW experiments because TBW calculated using the isotope dilution method was overestimated when blood samples were collected using reduviid bugs. In our validation experiment with nectar‐feeding bats (Glossophaga soricina), we compared estimates of daily energy expenditure (DEE) using DLW with those derived from the energy balance method. We considered Speakman's equation (controlling for 25% fractionated water loss) as the most appropriate for our study animal and calculated DEE accordingly. On average, DEE estimated with DLW was not significantly different from the mean value obtained with the energy balance method (mean deviation 1.2%). We conclude that although bug hemolymph or intestinal liquids most likely contaminate the samples, estimates of DEE are still valid because the DLW method does not depend on absolute isotope enrichments but on the rate of isotope decrease over time. However, dilution of blood with intestinal liquids or hemolymph from a bug may lead to larger variation in DEE estimates. We also tested how the relative error of DLW estimates changed with varying assumptions about fractionation. We used three additional equations for calculating DEE in DLW experiments. The basic equation for DLW experiments published by Lifson and McClintock (LM‐6) assumes no fractionation, resulted in an overestimate of DEE by 10%. Nagy's equation (N‐2) controls for changes in body mass but not for fractionation. Using Nagy's equation, DEE was overestimated by 8%. Under the assumption that 50% of total water flux fractionates, the alternative equation by Lifson and McClintock (LM‐35) DEE was underestimated by 5%. The best fit between estimates of DEE based on DLW and energy balance measurements was derived by assuming that 32% of total water flux (TWF) is fractionated. We conclude that the outcome of DLW experiments is sensitive to assumptions regarding evaporative water loss, and thus recommend Speakman's equation 7.17 for use with bats. J. Exp. Zool. 296A:87–97, 2003.Keywords
This publication has 22 references indexed in Scilit:
- Repeatability of Daily Field Metabolic Rate in Female Meadow Voles (Microtus pennsylvanicus)Functional Ecology, 1996
- Measurement of fractionated water loss and CO2production using triply labelled waterJournal of Theoretical Biology, 1988
- A new method for obtaining blood from a small mammal without injuring the animal: use of Triatomid bugsCellular and Molecular Life Sciences, 1986
- Food Passage and Intestinal Nutrient Absorption in HummingbirdsThe Auk, 1986
- Multi-sample conversion of water to hydrogen by zinc for stable isotope determinationAnalytical Chemistry, 1985
- Nectar intake and energy expenditure in a flower visiting batOecologia, 1984
- Use of doubly-labeled water (3HH18O) for determination of H2O flux and CO2 production by a mammal in a humid environmentOecologia, 1983
- Reduction of water with zinc for hydrogen isotope analysisAnalytical Chemistry, 1982
- Theory of use of the turnover rates of body water for measuring energy and material balanceJournal of Theoretical Biology, 1966
- Measurement of Total Carbon Dioxide Production by Means of D2O18Journal of Applied Physiology, 1955