School of Biological Sciences, Southern Illinois University, Carbondale, IL, 62901, USA.
Department of Biology, University of New Mexico, Albuquerque, NM, USA.
Rapid Commun Mass Spectrom. 2021 Mar 30;35(6):e9030. doi: 10.1002/rcm.9030.
Nitrogen stable isotope ratio (δ N) processes are not well described in reptiles, which limits reliable inference of trophic and nutrient dynamics. In this study we detailed δ N turnover and discrimination (Δ N) in diverse tissues of two lizard species, and compared these results with previously published carbon data (δ C) to inform estimates of reptilian foraging ecology and nutrient physiology.
We quantified N incorporation and discrimination dynamics over 360 days in blood fractions, skin, muscle, and liver of Sceloporus undulatus and Crotaphytus collaris that differed in body mass. Tissue samples were analyzed on a continuous flow isotope ratio mass spectrometer.
Δ N for plasma and red blood cells (RBCs) ranged between +2.7 and +3.5‰; however, skin, muscle, and liver did not equilibrate, hindering estimates for these somatic tissues. N turnover in plasma and RBCs ranged from 20.7 ± 4 to 303 ± 166 days among both species. Comparison with previously published δ C results for these same samples showed that N and C incorporation patterns were uncoupled, especially during winter when hibernation physiology could have played a role.
Our results provide estimates of N turnover rates and discrimination values that are essential to using and interpreting isotopes in studies of diet reconstruction, nutrient allocation, and trophic characterization in reptiles. These results also suggest that somatic tissues can be unreliable, while life history shifts in nutrient routing and metabolism potentially cause N and C dynamics to be decoupled.
氮稳定同位素比值（δN）过程在爬行动物中描述得还不够完善，这限制了对营养动态和营养动态的可靠推断。在这项研究中，我们详细描述了两种蜥蜴物种的不同组织中的δN 周转率和鉴别率（ΔN），并将这些结果与之前发表的碳数据（δC）进行了比较，以了解爬行动物觅食生态学和营养生理学的估计。
我们在血液成分、皮肤、肌肉和肝脏中定量了 360 天的 N 掺入和鉴别动力学，这些组织在体重上有差异。组织样本在连续流动同位素比质谱仪上进行分析。
血浆和红细胞（RBC）的 ΔN 在+2.7 到+3.5‰之间；然而，皮肤、肌肉和肝脏没有达到平衡，这阻碍了对这些体组织的估计。血浆和 RBC 中的 N 周转率在两个物种中从 20.7±4 到 303±166 天不等。与这些相同样本的先前发表的 δC 结果进行比较表明， N 和 C 的掺入模式是解耦的，尤其是在冬眠生理学可能发挥作用的冬季。
我们的研究结果提供了 N 周转率和鉴别值的估计值，这些估计值对于使用和解释同位素在饮食重建、营养分配和爬行动物营养特征研究中是必不可少的。这些结果还表明，体组织可能不可靠，而营养物质运输和代谢的生活史变化可能导致 N 和 C 动态解耦。
