Water flux in animals: analysis of potential errors in the tritiated water method (original) (raw)
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2021
Understanding physiological traits and ecological conditions that influence a species reliance on metabolic water is critical to creating accurate physiological models that can assess their ability to adapt to environmental perturbations (e.g., drought) that impact water availability. However, relatively few studies have examined variation in the sources of water animals use to maintain water balance, and even fewer have focused on the role of metabolic water. A key reason is methodological limitations. Here, we applied a new method that measures the triple oxygen isotopic composition of a single blood sample to estimate the contribution of metabolic water to the body water pool of three passerine species. This approach relies on Δ\u2717O, defined as the residual from the tight linear correlation that naturally exists between δ17O and δ18O values. Importantly, Δ\u2717O is relatively insensitive to key fractionation processes, such as Rayleigh distillation in the water cycle that hav...
Journal of applied physiology (Bethesda, Md. : 1985), 2003
This study uses indirect calorimetry to assess the effects of humidity on the accuracy of the doubly labeled water (DLW) technique to predict metabolic rate and water flux in brown treesnakes (Boiga irregularis). The DLW technique accurately predicted total water efflux in brown treesnakes under low-humidity conditions and found that the total number of water molecules exchanged with the environment under humid conditions was not significantly different than maximum net total evaporative water loss under low humidity conditions plus fecal water loss. Because of changes of total body water of >12%, the DLW technique overestimated metabolic rate by a factor of 2.2 under low-humidity conditions. Under high-humidity conditions, the DLW technique overestimated metabolic rate in brown treesnakes by a factor of 4.6. Researchers using the DLW technique in humid or moist environments should be cautious because this study indicates that DLW estimates of metabolic rate may be inflated when ...
Faeces is a reliable source of body water for measuring tritium in reindeer in summer and in winter
Rangifer, 1995
Rates of equilibration and subsequent wash-out of tritium were measured in parallel samples of blood, rumen fluid and faeces collected from two adult female Norwegian reindeer in summer and in winter. The tritium-concentration was the same in all three body water compartments after no more than 9 h following both intravenous and intraruminal injection of isotope in summer and following intravenous injection of isotope in winter. The biological half-life of the tritium increased from approximately 3 days in summer to approximately 10 days in winter, probably as a consequence of a decrease in water intake. There were no significant differences in disappearance rates of tritium from blood, rumen fluid and faeces within any of the six experiments. Fresh faeces is therefore a reliable source of body water that can be used in place of blood in studies of body water kinetics in reindeer, thus making it potentially possible to conduct such studies on truly free-living and undisturbed animals.
Validation of Water Flux and Body Composition in Glaucous Gulls ( Larus hyperboreus )
Physiological and Biochemical Zoology, 2006
Water influx rates (WIR) measured with tritiated water dilution were compared with direct measures of water and energy intake in glaucous gulls (Larus hyperboreus). Total body water (TBW) measured isotopically was also compared with TBW determined by body composition analysis (BCA) of the same birds. Seventeen wild gulls were captured and studied in outdoor enclosures at Ny-Å lesund, Svalbard, in July 2002. Gulls were hand-fed known quantities of Arctic cod (Boreogadus saida) or given water on the basis of one of four experimental treatments: (A) fasting, (B) fish only, (C) water only, or (D) fish and water. Water and energy content of Arctic cod was also determined. WIR of gulls (after subtracting metabolic water production) in treatments A, B, C, and D were 0, , , and 101 ע 5 ע26 19 SD g d Ϫ1 , respectively. Measured water intake in each 122 ע 21 group was 0, , , and SD g d Ϫ1 , respec-111 ע 2 64 ע 3 ע431 15 tively. On average, WIR underestimated measured water intake in each group. Errors were lowest but most variable for gulls fed water only ( ) compared with gulls fed fish Ϫ2.2% ע 32.8% only ( ) or fish and water ( ). Ϫ9.0% ע 5.4%
Evaporative water loss in scaleless snakes
Comparative biochemistry and physiology. A, Comparative physiology, 1975
1. Rates of water loss were measured in two aberrant scaleless water snakes, Natriu sipedon, and in six normal animals.
Oecologia, 2004
Naturally-occurring deuterium stable isotope ratios can potentially be used to trace water resource use by animals, but estimating the contribution of isotopically distinct water sources requires the accurate prediction of isotopic discrimination factors between water inputs and an animal's body water pool. We examined the feasibility of using estimates of water fluxes between a bird and its environment with a mass-balance model for the deuterium stable isotope ratio of avian body water (δD body ) to predict isotopic discrimination factors. Apparent fractionation and thus discrimination factors were predicted to vary with the proportion of an animal's total water losses than could be attributed to evaporative processes. To test our ability to predict isotopic discrimination, we manipulated water intake and evaporative water loss in rock doves (Columba livia) by providing them with fresh water or 0.15 M NaCl solution in thermoneutral or hot environments. After we switched the birds from drinking water with δD=−95‰ VSMOW (Vienna Standard Mean Ocean Water) to enriched drinking water with δD=+52‰ VSMOW, steady-state δD body was approached asymptotically. The equilibrium δD body was enriched by 10-50‰ relative to water inputs. After isotopic equilibrium was reached, the degree of enrichment was positively related (r 2 =0.34) to the fraction of total water loss that occurred by evaporation r evap =r H 2 O À Á supporting the major prediction of the model. The variation we observed in discrimination factors suggests that the apparent fractionation of deuterium will be difficult to predict accurately under natural conditions. Our results show that accurate estimates of the contribution of different water sources to a bird's body water pool require large deuterium isotopic differences between the sources.
Fluxes of carbon, nitrogen, and water between ecosystem components and organisms have great impacts across levels of biological organization. Although much progress has been made in tracing carbon and nitrogen, difficulty remains in tracing water sources from the ecosystem to animals and among animals (the ‘‘water web’’). Naturally occurring, nonradioactive isotopes of hydrogen and oxygen in water provide a potential method for tracing water sources. However, using this approach for terrestrial animals is complicated by a change in water isotopes within the body due to differences in activity of heavy and light isotopes during cuticular and transpiratory water losses. Here we present a technique to use stable water isotopes to estimate the mean mix of water sources in a population by sampling a group of sympatric animals over time. Strong correlations between H and O isotopes in the body water of animals collected over time provide linear patterns of enrichment that can be used to predict a mean mix of water sources useful in standard mixing models to determine relative source contribution. Multiple temperature and humidity treatment levels do not greatly alter these relationships, thus having little effect on our ability to estimate this population-level mix of water sources. We show evidence for the validity of using multiple samples of animal body water, collected across time, to estimate the isotopic mix of water sources in a population and more accurately trace water sources. The ability to use isotopes to document patterns of animal water use should be a great asset to biologists globally, especially those studying drylands, droughts, streamside areas, irrigated landscapes, and the effects of climate change.
Isotopes in Environmental and Health Studies, 2006
We have used the isotope dilution technique to study changes in the body composition of a migratory shorebird species (Red Knot, Calidris canutus) through an assessment of the amount of body water in it. Birds were quantitatively injected with a dose of water with elevated concentrations of 2 H, 17 O, and 18 O. Thereafter, blood samples were taken and distilled. The resulting water samples were analysed using an isotope ratio mass spectrometry (for 2 H and 18 O only) and a stable isotope ratio infrared laser spectrometry ( 2 H, 17 O, and 18 O) to yield estimates of the amount of body water in the birds, which in turn could be correlated to the amount of body fat. Here, we validate laser spectrometry against mass spectrometry and show that all three isotopes may be used for body water determinations. This opens the way to the extension of the doubly labelled water method, used for the determination of energy expenditure, to a triply labelled water method, incorporating an evaporative water loss correction on a subject-by-subject basis or, alternatively, the reduction of the analytical errors by statistically combining the 17 O and 18 O measurements.
Journal of Animal Science, 2013
Water is an essential nutrient necessary to support life, and adequate water supply is crucial for animal survival and productivity. The present study was designed to determine seasonal changes in the water metabolism of horses under outdoor conditions. Total body water (TBW) and total water intake (TWI) of 10 adult Shetland pony mares were estimated at monthly intervals for 14 mo by using the deuterium dilution technique. During the last 4 mo, 5 ponies were fed restrictively to simulate natural feed shortage in winter, and 5 ponies served as controls. The TBW (kg) was closely related to body mass [TBW (kg) =-2.86 + 0.67 × body mass (kg); P < 0.001; n = 105] explaining 86% of the variation. In contrast to TBW (kg), TBW (%) remained relatively stable across all measurements (57.8 to 71.2%). The TWI showed an increase in summer and a decrease in winter [TWI (mL•kg-1 •d-1) = 15.07 + 23.69 × month-1.45 × month 2 (R 2 = 0.64, P < 0.01)]. However, TWI measured at ambient temperatures (T a) < 0°C did not follow the same trend as TWI at T a > 0°C. Therefore, removing TWI values measured at T a < 0°C from the analysis resulted in high correlations with locomotor activity (r = 0.87), T a (r = 0.86), and resting heart rate (r = 0.88). The multiple regression among TWI, T a , and heart rate explained 84% of the variation in TWI [TWI (mL•kg-1 •d-1) =-13.38 + 1.77 × heart rate (beats/min) + 2.11 × T a (°C); P < 0.001]. Feed restriction had no effect on TWI and TBW. The TBW content was unaffected by season and physical activity. The established regression equation for TBW and body mass can be used to predict TBW from body mass in ponies under field conditions. The comparison of TWI with published data on drinking water intake revealed that ponies had 1.7 to 5.1 times greater total water intakes when other sources of water such as feed and metabolic water were included. The TWI was highly influenced by environmental conditions and metabolic rate. Contrary to expectation, water supply during the cold seasons might be more critical than under summer conditions when water content of grass is high to allow for the compensation of limited availability of drinking water.