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

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.

Turnover and fractionation of nitrogen stable isotope in tissues of grass carp Ctenopharyngodon idellus

“…2 & 3), which indicates that the tissue turnover might be attributable to both tissue replacement in the form of metabolism (m) and net tissue increase in the form of growth (k). Metabolic contributions to nitrogen isotopic turnover reached approximately 70−77% and 39−47% for liver and muscle, respectively, while 86−90% contribution of growth to nitrogen isotopic turnover was strongly correlated with less metabolic activity of gill, and reflected that growth played a more important role in the long-term isotopic turnover of gill (Tables 2 & 3 Previous studies have demonstrated that the discrepancy in turnover rates between tissues is mainly driven by variable metabolic contributions to the isotopic turnover process (Arneson & MacAvoy 2005, MacAvoy et al 2006. The relative importance of metabolism versus growth in nitrogen isotopic turnover is determined by bioenergetic allocations.…”

“…Previous studies have demonstrated that the discrepancy in turnover rates between tissues is mainly driven by variable metabolic contributions to the isotopic turnover process (Arneson & MacAvoy 2005, MacAvoy et al 2006. The relative importance of metabolism versus growth in nitrogen isotopic turnover is determined by bioenergetic allocations.…”

Carbon stable isotope turnover and fractionation in grass carp Ctenopharyngodon idella tissues

“…Previous studies have demonstrated that the discrepancies of turnover rates between tissues were mainly driven by variable metabolic contributions to the turnover process. EvansOgden et al (2004), Arneson & MacAvoy (2005) and MacAvoy et al (2006) all suggested that the carbon isotopic turnover rates were correlated strongly with the metabolic rate of tissue involved. The faster the metabolism, the quicker the turnover rate and therefore the shorter the half-life of the tissue.…”

Nutritional contribution of torula yeast and fish meal to the growth of shrimp Litopenaeus vannamei as indicated by natural nitrogen stable isotopes

“…The growth rate constant, k, was estimated by fitting an exponential growth model to observed weight data, k =log(final weight/initial weight)/time(d), while parameter m was obtained using iterative non-linear regression. Coefficients k and m provide an indicator of the time period necessary for half of the muscle nitrogen to be replaced by new nitrogen after animals consume a new diet (half life, t 50 ) (MacAvoy et al 2006).…”