Murray Ian W, Wolf Blair O
Department of Biology, University of New Mexico, Albuquerque, New Mexico 87131.
Physiol Biochem Zool. 2012 Jan-Feb;85(1):96-105. doi: 10.1086/663867. Epub 2012 Jan 3.
Abstract Understanding carbon incorporation rates and diet-to-tissue discrimination (Δ(13)C(tissue-diet)) in animals is necessary to interpret stable isotope data collected from animals in the field. Our current understanding of the carbon dynamics in terrestrial ectotherms such as snakes, lizards, and turtles is poorly developed. Here we use a diet switch experiment to estimate carbon incorporation rates and diet-to-tissue discrimination factors in growing desert tortoises (Gopherus agassizii). Average carbon retention times for red blood cells (RBCs) and plasma were 126.7 ± 40.3 and 32.9 ± 14.5 days, respectively. Tissue carbon incorporation rates were affected by both growth and metabolism, with growth accounting for 50% of the carbon turnover in RBCs and 13% of carbon turnover in plasma. At equilibrium, scute keratin (0.8 ± 0.1) and plasma (1.0 ± 0.2) showed enriched discrimination values (Δ(13)C) compared to the test diet, but RBC Δ(13)C values were indistinguishable from diet (0.2 ± 0.3). We also found that new keratin continued to contribute significant material to previously grown keratin rings on the tortoise's shell. Changes in the δ(13)C of previously laid down growth rings indicated that the old rings closest to the region of new growth received about 73% of the carbon from the current diet; these data suggest that the interpretation of dietary history using growth rings must recognize that each ring may represent the weighted average of the diet over several seasons. These results continue to highlight the importance of laboratory experiments in interpreting isotopic data derived from field studies.
摘要 了解动物体内的碳掺入率和饮食到组织的同位素分馏（Δ(13)C(tissue-diet)）对于解释在野外从动物身上收集的稳定同位素数据至关重要。我们目前对蛇、蜥蜴和海龟等陆地变温动物碳动态的了解还很有限。在这里，我们通过饮食转换实验来估计生长中的沙漠陆龟（Gopherus agassizii）的碳掺入率和饮食到组织的同位素分馏因子。红细胞（RBC）和血浆的平均碳保留时间分别为126.7±40.3天和32.9±14.5天。组织碳掺入率受生长和代谢的影响，生长分别占红细胞碳周转率的50%和血浆碳周转率的13%。在平衡状态下，盾片角蛋白（0.8±0.1）和血浆（1.0±0.2）与测试饮食相比显示出富集的同位素分馏值（Δ(13)C），但红细胞的Δ(13)C值与饮食无法区分（0.2±0.3）。我们还发现，新的角蛋白继续为陆龟壳上先前生长的角蛋白环贡献大量物质。先前形成的生长环的δ(13)C变化表明，最接近新生长区域的旧环从当前饮食中获得了约73%的碳；这些数据表明，利用生长环解释饮食历史时必须认识到每个环可能代表几个季节饮食的加权平均值。这些结果继续凸显了实验室实验在解释从野外研究获得的同位素数据方面的重要性。
