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 δ13C and δ15N in whole blood was determined. Basal metabolic rates (as CO2 output and O2 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 O2/min/g), had a slower blood turnover than mice for 13C (t 1/2=24.8 and 17.3 days, respectively) and 15N (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.

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Available from: Stephen E Macavoy, Aug 28, 2015
    • "Several studies have suggested that isotopic turnover rates are correlated with metabolic rate and body size (Bearhop et al., 2002; MacAvoy et al., 2006), an indirect relationship probably mediated by protein turnover (Carleton and Martínez del Rio, 2005), which may explain why the isotopic turnover rate in dunlins is more similar to a passerine than to its larger congener or other larger birds. In our study, the turnover rate of δ 13 C tended to be faster than that of δ 15 N, a result consistent with some studies (Hobson and Barlein, 2003; Pearson et al., 2003), but not with others (Bearhop et al., 2003; Ogden et al., 2004). "
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    ABSTRACT: Most stable isotope (SI) applications in avian ecology are based on the analysis of feathers and blood, whereas toenails are much less used. These structures grow slowly and continuously, thus integrating information over comparatively longer periods which may be useful for migration connectivity studies, while avoiding some of the difficulties posed by incomplete information on feather molt. In spite of this, interpretation of data from toenails is limited by lack of accurate figures on their turnover rates and discrimination values. To improve our understanding of SI ratios in toenails and surpass these drawbacks we measured the change in carbon (δ13C) and nitrogen (δ15N) SI ratios in plasma, red blood cells and toenails of captive dunlins Calidris alpina after a controlled diet switch. Discrimination values were estimated by comparing isotopic values at the end of the experiment with those of artificial food. We also estimated toenail growth rates in this species. Toenails showed much lower SI turnover rates than blood components, with half-lives of 27 days and 35 days for δ13C and δ15N, respectively. Isotopic ratios in toenails reached equilibrium with the new diet after 100–120 days, roughly coinciding with the duration of toenail replacement. The discrimination values of 2.74 ± 0.68‰ for δ13C and 4.06 ± 0.27‰ for δ15N found for toenails are higher than those of both blood components. These values are also higher than most published values for blood in other avian species, but similar to those previously reported for feathers which, like toenails, are metabolically inert after synthesis and are mainly composed of keratin. This study highlights the potential role of toenails as sources of SI data for ecological studies, particularly to determine geographic origin of birds migrating between isotopically distinct environments. Indeed, their long turnover rates might allow for the detection of SI signals from the wintering or breeding ranges, by sampling individuals at their staging sites. Isotopic turnover in toenails follow their replacement rates, and these seem to be rather similar across several avian taxa. Thus, the turnover rates described here may potentially be used to interpret SI data for other birds.
    Journal of Experimental Marine Biology and Ecology 11/2015; 472:89-96. DOI:10.1016/j.jembe.2015.07.006 · 2.48 Impact Factor
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    • "While it is essential to evaluate stable isotope dynamics across diverse species, there is a taxonomic bias in research on TDFs and isotopic incorporation rates within the vertebrates. Most studies have focused on fish, birds, and mammals (fish: Bosley et al. 2002; Logan et al. 2006; Suring and Wing 2009; Carleton and Martínez del Rio 2010; Hussey et al. 2010; Logan and Lutcavage 2010; Nelson et al. 2011; Kim et al. 2012; Heady and Moore 2013; birds: Hobson and Clark 1992a, 1992b; Bearhop et al. 2002; Ogden et al. 2004; Cherel et al. 2005; Hobson and Yohannes 2007; Bauchinger and McWilliams 2009; Connan et al. 2014; mammals: Tieszen et al. 1983; Roth and Hobson 2000; Lesage et al. 2002; MacAvoy et al. 2006; Stegall et al. 2008; Florin et al. 2011; Browning et al. 2014). Recent studies have also investigated TDFs and incorporation rates in reptiles (Seminoff et al. 2007, 2009; Reich et al. 2008; Fisk et al. 2009; Warne et al. 2010; Murrary and Wolf 2013). "
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    ABSTRACT: Stable isotope analysis is an increasingly useful ecological tool, but its accuracy depends on quantifying the tissue-specific trophic discrimination factors (TDFs) and isotopic incorporation rates for focal taxa. Despite the technique's ubiquity, most laboratory experiments determining TDFs and incorporation rates have focused on birds, mammals, and fish; we know little about terrestrial ectotherms, and amphibians in particular are understudied. In this study we used two controlled feeding experiments to determine carbon (d 13 C) and nitrogen (d
    Physiological and Biochemical Zoology 07/2015; 88(5):576. DOI:10.1086/682576 · 2.05 Impact Factor
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    • "Future studies using a series of repeated feedings could be useful to study the rate of carbon turnover in the lipid stores of these animals. Presently most of our knowledge of carbon turnover in vertebrates comes from endothermic models /e.g.,(Voigt et al., 2003; MacAvoy and Arneson, 2006; Bauchinger and McWilliams, 2010)/. "
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