Article

Correlation of metabolism with tissue carbon and nitrogen turnover rate in small mammals.

Department of Biology, American University, Hurst Hall 101, 4400 Massachusetts Ave NW, Washington, DC 202-885-2186, USA.
Oecologia (Impact Factor: 3.25). 12/2006; 150(2):190-201. DOI: 10.1007/s00442-006-0522-0
Source: PubMed

ABSTRACT Stable isotopes have proven to be a useful tool for deciphering food webs, examining migration patterns and determining nutrient resource allocation. In order to increase the descriptive power of isotopes, an increasing number of studies are using them to model tissue turnover. However, these studies have, mostly by necessity, been largely limited to laboratory experiments and the demand for an easier method of estimating tissue turnover in the field for a large variety of organisms remains. In this study, we have determined the turnover rate of blood in mice and rats using stable isotope analysis, and compared these rates to the metabolic rates of the animals. Rats (Rattus norvegicus) (n=4) and mice (Mus musculus) (n=4) were switched between isotopically distinct diets, and the rate of change of delta(13)C and delta(15)N in whole blood was determined. Basal metabolic rates (as CO(2) output and O(2) consumption per unit time, normalized for mass) were determined for the rats and mice. Rats, which were an order of magnitude larger and had a slower metabolic rate per unit mass than mice (0.02 vs. 0.14 O(2)/min/g), had a slower blood turnover than mice for (13)C (t (1/2 )=24.8 and 17.3 days, respectively) and (15)N (t (1/2 )=27.7 and 15.4 days, respectively). A positive correlation between metabolic rate and blood isotopic turnover rate was found. These are the only such data for mammals available, but the literature for birds shows that mass and whole-body metabolic rates in birds scale logarithmically with tissue turnover. Interestingly, the mammalian data graph separately from the bird data on a turnover versus metabolic rate plot. Both mice and rat tissue in this study exhibited a slower turnover rate compared to metabolic rate than for birds. These data suggest that metabolic rate may be used to estimate tissue turnover rate when working with organisms in the field, but that a different relationship between tissue turnover and metabolism may exist for different classes of organisms.

Full-text

Available from: Stephen E Macavoy, May 28, 2015
0 Followers
 · 
76 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Broad-scale food web inferences of 534 albacore tuna, Thunnus alalunga, in the south-west Pacific Ocean in 2009 and 2010 were made using bulk nitrogen (δ15N) and carbon (δ13C) stable isotopes. Condition was also examined for the same fish using C:N ratios. A Generalized Additive Modeling (GAM) approach was used to analyze spatio-temporal, biological and environmental drivers that impact the distribution of tuna isotopes and to create oceanographic maps. Based on model formulations, five bioregions with distinct isotopic signatures were identified and were related to known biological, nutrient cycling and oceanographic (temperature, primary productivity and eddy) features associated with the East Australian Current. δ15N values showed a large-scale, uniform latitudinal gradient decreasing from the south to north, in a region encompassing oligotrophic waters in the Coral Sea. In contrast, δ13C values were lower in the nutrient rich Tasman Sea waters and offshore East Australia. C:N ratios suggested that tuna occupying southern and offshore waters were in better condition. Ontogenetic trends in all three biochemical parameters were identified and related to differences in size distribution. Regional-specific temporal variations were detected including similar monthly changes for both isotopes and significantly less enriched δ13C (by 1.9‰) than in previous work undertaken in 2006, potentially signifying a substantial shift in the carbon cycle that supports food webs off central east Australia. Our results showed that isotopic measurements in tuna and the GAM framework provide powerful tools to assess ecosystem functioning and change by linking sources of nutrients and organic matter to local food web assembly. Such knowledge is vital to support an ecosystem based approach to fisheries management including biogeochemical whole-of-ecosystem models and monitoring programs at regional and landscape-scales.
    Progress In Oceanography 03/2015; 134. DOI:10.1016/j.pocean.2015.03.001 · 3.99 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Pythons digesting rodent meals exhibit up to 10-fold increases in their resting metabolic rates (RMR); this increase in RMR is termed specific dynamic action (SDA). Studies have shown that SDA is partially fuelled by oxidizing dietary nutrients, yet it remains unclear whether the proteins and the lipids in their meals contribute equally to this energy demand. We raised two populations of mice on diets labeled with either 13C-leucine or 13C-palmitic acid to intrinsically enrich the proteins and lipids in their bodies, respectively. Ball pythons (Python regius) were fed whole mice (and pureed mice three weeks later) after which we measured their metabolic rates and the δ13C in the breath. The δ13C in the whole bodies of the protein- and lipid-labeled mice were generally similar (i.e., 5.7±4.7‰ and 2.8±5.4‰, respectively) but the oxidative kinetics of these two macronutrient pools were quite different. We found that the snakes oxidized 5% of the protein and only 0.24% of the lipids in their meals within 14 days. Oxidation of the dietary proteins peaked 24 h after ingestion at which point these proteins provided ~90% of the metabolic requirement of the snakes and by 14 d the oxidation of these proteins decreased to nearly zero. The oxidation of the dietary lipids peaked one day later at which point these lipids supplied ~25% of the energy demand. Fourteen days after ingestion these lipids were still being oxidized and continued to account for ~25% of the metabolic rate. Pureeing the mice reduced the cost of gastric digestion and decreased SDA by 24%. Pureeing also reduced the oxidation of dietary proteins by 43%, but it had no effect on the rates of dietary lipid oxidation. Collectively, these results demonstrate that pythons are able to effectively partition the two primary metabolic fuels in their meals. This approach of uniquely labeling the different components of the diet will allow researchers to examine new questions about how and when animals use the nutrients in their meals.
    Journal of Experimental Biology 01/2015; in press. · 3.00 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Pythons digesting rodent meals exhibit up to 10-fold increases in their resting metabolic rates (RMR); this increase in RMR is termed specific dynamic action (SDA). Studies have shown that SDA is partially fuelled by oxidizing dietary nutrients, yet it remains unclear whether the proteins and the lipids in their meals contribute equally to this energy demand. We raised two populations of mice on diets labeled with either (13)C-leucine or (13)C-palmitic acid to intrinsically enrich the proteins and lipids in their bodies, respectively. Ball pythons (Python regius) were fed whole mice (and pureed mice three weeks later) after which we measured their metabolic rates and the δ(13)C in the breath. The δ(13)C in the whole bodies of the protein- and lipid-labeled mice were generally similar (i.e., 5.7±4.7‰ and 2.8±5.4‰, respectively) but the oxidative kinetics of these two macronutrient pools were quite different. We found that the snakes oxidized 5% of the protein and only 0.24% of the lipids in their meals within 14 days. Oxidation of the dietary proteins peaked 24 h after ingestion at which point these proteins provided ∼90% of the metabolic requirement of the snakes and by 14 d the oxidation of these proteins decreased to nearly zero. The oxidation of the dietary lipids peaked one day later at which point these lipids supplied ∼25% of the energy demand. Fourteen days after ingestion these lipids were still being oxidized and continued to account for ∼25% of the metabolic rate. Pureeing the mice reduced the cost of gastric digestion and decreased SDA by 24%. Pureeing also reduced the oxidation of dietary proteins by 43%, but it had no effect on the rates of dietary lipid oxidation. Collectively, these results demonstrate that pythons are able to effectively partition the two primary metabolic fuels in their meals. This approach of uniquely labeling the different components of the diet will allow researchers to examine new questions about how and when animals use the nutrients in their meals. © 2015. Published by The Company of Biologists Ltd.
    Journal of Experimental Biology 05/2015; DOI:10.1242/jeb.118349 · 3.00 Impact Factor