Isotope incorporation in broad-snouted caimans (crocodilians)

The trophic ecology and migration of vertebrate species have been increasingly studied using stable isotope analysis. However, this approach requires knowledge on how dietary isotopic values are reflected in consumers' tissues. To date, this information has only been obtained for a handful of ectotherms; in particular, little is known about crocodilians. In this study, diet-tissue discrimination factors (DTDFs) and carbon and nitrogen stable isotope turnover rates were estimated for plasma, red blood cells (RBCs), and muscle obtained from broad-snouted caimans (Caiman latirostris). Individuals were fed two different control diets for 189 days. DTDFs for δ(15)N (Δ(15)N) and δ(13)C (Δ(13)C) ranged from -2.24‰ to 0.39‰ and from -0.52‰ to 1.06‰, respectively. Isotope turnover rates in tissues, expressed as half-lives, ranged from 11 to 71 days, with plasma<muscle<RBCs. Δ(15)N was found to be particularly small, even when compared to values found for other ectotherms, a result that may be linked to the unique excretion physiology of crocodilians. These stable isotope incorporation data should help inform future interpretations of isotopic values obtained in the field for this taxon.