This study explores the effects of seasonal dormancy on the turnover rate and isotopic discrimination factors of carbon (δ 13C) and nitrogen (δ 15N) in the tissues of Salvator merianae, also known as the Tegu lizard. Both adult and juvenile lizards were monitored through various phases, including pre-dormancy, active periods, and arousal from dormancy. The isotopic analysis revealed that plasma has a faster turnover rate compared to red blood cells, with adults exhibiting turnover half-lives of 23 days for δ 13C in plasma, while juveniles showed a broader range due to slower adaptation. Interestingly, the study found that the isotopic discrimination factors varied between the two tissues, with adults displaying greater enrichment of δ 15N in plasma during dormancy arousal, suggesting significant mobilization of endogenous amino acids. Additionally, the results highlight the role of facultative endothermy during reproduction, which appears to accelerate isotopic turnover in both adults and juveniles. Despite minimal body mass loss during dormancy, the metabolic processes involved, such as lipid mobilization and protein catabolism, were crucial in sustaining the lizards. The variability in isotopic discrimination factors observed in this study underscores the complexity of metabolic adaptations in Salvator merianae, particularly in response to prolonged fasting and seasonal dormancy. These findings provide deeper insights into the physiological strategies employed by ectotherms to cope with extreme environmental conditions.

Rationale: Rapid coagulation of reptile blood often hinders its use in studies in remote and difficult-to-access areas, necessitating chemical preservation. Therefore, understanding the potential effects of anticoagulants on the isotopic compositions of blood is essential to avoid issues in interpreting the results of ecological studies. In this study we aimed to verify whether the storage time of the blood tissue in anticoagulants can influence its isotopic compositions of the broad-snouted caiman ( Caiman latirostris), an ectothermic top predator from eastern South America. Methods: Blood samples were obtained from ten adult females of C. latirostris from a commercial breeding facility in 2015. Samples were stored in vials containing EDTA and SH and centrifuged after 2 and 8 hours to separate red blood cells and plasma. Results: No effect of time was found on the δ 13C and δ 15N of whole blood, plasma, and red cells in contact with the two types of anticoagulants, EDTA and SH. Conclusion: The findings have practical implications for researchers in this field, as they suggest that anticoagulants can be used effectively for at least eight hours under refrigeration.