Metabolic turnover rates of carbon and nitrogen stable isotopes in captive juvenile snakes
Rapid Communications in Mass Spectrometry
Metabolic turnover rates (m) of δ15N and δ13C were assessed in different tissues of newly hatched captive-raised corn snakes (Elaphe guttata guttata) fed maintenance diets consisting of earthworms (Eisenia foetida) that varied substantially in δ15N (by 644%) and δ13C (by 5.0%). Three treatments were used during this 144 day experiment that consisted of the same diet throughout (control), shifting from a depleted to an enriched stable isotope signature diet (uptake), and shifting from an enriched to depleted stable isotope signature diet (elimination). Values of δ13C in the liver, blood, and muscle of the control snakes reached equilibrium with and were, respectively, 1.73, 2.25 and 2.29 greater than in their diet, this increase is called an isotopic discrimination factor (Δδ 13C = δ13Csnake - δ 13Cfood). Values of δ15N in snake tissues did not achieve equilibrium with the diets in any of the exposures and thus Δ15N could not be estimated. Values of metabolic turnover rates (m) for δ13C and δ15N were greater in liver than in muscle and blood, which were similar, and relative results remained the same if the fraction of 15N and 13C were modeled. Although caution is warranted because equilibrium values of stable isotopes in the snakes were not achieved, values of m were greater for δ13C than δ15N, resulting in shorter times to dietary equilibrium for δ13C upon a diet shift, and for both stable isotopes in all tissues, greater during an elimination than in an uptake shift in diet stable isotope signature. Multiple explanations for the observed differences between uptake and elimination shifts raise new questions about the relationship between animal and diet stable isotope concentrations. Based on this study, interpretation of feeding ecology using stable isotopes is highly dependent on the kind of stable isotope, tissue, direction of diet switch (uptake versus elimination), and the growth rate of the animal. Copyright © 2009 John Wiley & Sons, Ltd.
Fisk, Aaron T.; Sash, Kim; Maerz, John; Palmer, William; Carroll, John P.; and MacNeil, M. Aaron. (2009). Metabolic turnover rates of carbon and nitrogen stable isotopes in captive juvenile snakes. Rapid Communications in Mass Spectrometry, 23 (2), 319-326.