Compound specific nitrogen isotope analysis of amino acids (AA CSIA) has been used to study the trophic ecology of many marine organisms because of its ability to characterize the δ15N value at the base of a food web while simultaneously providing trophic position information from a single tissue sample of a consumer. Although application of this method is becoming more widely used in trophic studies, critical assumptions such as amino acid designation and trophic discrimination factors remain unresolved for many taxa and tissue types. In this study, we used captive green turtles (Chelonia mydas) in a controlled feeding study to determine and evaluate individual amino acid isotope fractionation patterns and trophic discrimination factors (TDFs) for skin and plasma. Our data build on findings from previous studies that show that the traditional paradigm of using glutamic acid and phenylalanine as trophic and source amino acids, respectively, for trophic position estimation is consistent for green turtles; we also provide evidence to support the potential utility of other combinations of amino acids for trophic position calculations. Green turtle TDFs for glutamic acid and phenylalanine were 4.0 ± 0.5 ‰ and 6.6 ± 0.7 ‰ for skin and plasma, respectively. We found serine to have the largest Δδ15N (turtle-diet discrimination) value of all amino acids in both skin and plasma, while lysine Δδ15N values were consistent for use as a source amino acid in skin and plasma tissue. We evaluated our TDFs by estimating trophic position of four sea turtle species using previously published amino acid isotope data. These results indicate that for green turtles, the traditional use of glutamic acid and phenylalanine along with a combination of trophic amino acids paired with lysine can provide robust trophic position estimates. Moreover, we highlight the taxa and tissue-specific nature of amino acid nitrogen isotope fractionation patterns in green turtle tissues and underscore that well-approximated TDFs can refine trophic position estimates for sea turtles.

中文翻译：

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绿海龟（Chelonia mydas）对照研究中氨基酸的氮同位素分馏：扩展到 Glx/Phe 以外的营养位置

氨基酸复合特定氮同位素分析 (AA CSIA) 已被用于研究许多海洋生物的营养生态学，因为它能够表征食物网底部的 δ15N 值，同时提供来自单个组织的营养位置信息消费者样本。尽管这种方法在营养研究中的应用越来越广泛，但对于许多分类群和组织类型，诸如氨基酸名称和营养区分因素等关键假设仍未得到解决。在这项研究中，我们在一项受控饲养研究中使用圈养绿海龟 (Chelonia mydas) 来确定和评估个体氨基酸同位素分馏模式和皮肤和血浆的营养鉴别因子 (TDF)。我们的数据建立在先前研究的结果之上，这些研究结果表明，分别使用谷氨酸和苯丙氨酸作为营养氨基酸和来源氨基酸进行营养位置估计的传统范式对于绿海龟是一致的；我们还提供证据支持其他氨基酸组合在营养位置计算中的潜在效用。皮肤和血浆中谷氨酸和苯丙氨酸的绿海龟 TDF 分别为 4.0 ± 0.5 ‰ 和 6.6 ± 0.7 ‰。我们发现丝氨酸在皮肤和血浆中的所有氨基酸中具有最大的 Δδ15N（海龟饮食区分）值，而赖氨酸 Δδ15N 值在用作皮肤和血浆组织中的源氨基酸时是一致的。我们通过使用先前公布的氨基酸同位素数据估计四种海龟物种的营养位置来评估我们的 TDF。这些结果表明，对于绿海龟，谷氨酸和苯丙氨酸的传统使用以及与赖氨酸配对的营养氨基酸的组合可以提供可靠的营养位置估计。此外，我们强调了绿海龟组织中氨基酸氮同位素分馏模式的分类群和组织特异性，并强调近似的 TDF 可以改进海龟的营养位置估计。