The measurement of stable isotope values of individual compounds, such as amino acids (AAs), has become a powerful tool in animal ecology and ecophysiology. As with any emerging technique, questions remain regarding the capabilities and limitations of this approach, including how metabolism and tissue synthesis impact the isotopic values of individual AAs and subsequent multivariate patterns. We measured carbon isotope (δ¹³C) values of essential (AA_ESS) and nonessential (AA_NESS) AAs in bone collagen, whisker, muscle, and liver from ten southern sea otters (Enhydra lutris nereis) that stranded in Monterey Bay, California. Sea otters in this population exhibit high degrees of individual dietary specialization, making this an excellent dataset to explore differences in AA δ¹³C values among tissues in a wild population. We found the δ¹³C values of the AA_NESS glutamic acid, proline, serine, and glycine and the AA_ESS threonine differed significantly among tissues, indicating possible isotopic discrimination during tissue synthesis. Threonine δ¹³C values were higher in liver relative to bone collagen and muscle, which may indicate catabolism of threonine for gluconeogenesis, an interpretation further supported by correlations between the δ¹³C values of threonine and its gluconeogenic products glycine and serine in liver. This intraindividual isotopic variation yielded different ecological interpretations among tissues; for 6/10 of the sea otter individuals analyzed, at least one tissue indicated reliance on a different primary producer source than the other tissues. Our results highlight the importance of gluconeogenesis in a carnivorous marine mammal and indicate that metabolic processes influence AA_ESS and AA_NESS δ¹³C values and multivariate AA δ¹³C patterns.

氨基酸 (AA) 等单个化合物的稳定同位素值的测量已成为动物生态学和生态生理学的强大工具。与任何新兴技术一样，关于这种方法的能力和局限性的问题仍然存在，包括新陈代谢和组织合成如何影响单个氨基酸的同位素值和随后的多元模式。我们测量了搁浅在加利福尼亚州蒙特利湾的 10 只南方海獭 ( EnHydra lutris nereis ) 的骨胶原、晶须、肌肉和肝脏中必需 (AA _ESS ) 和非必需 (AA _{NESS ) AA 的碳同位素 (} δ ¹³ C ) 值。该种群中的海獭表现出高度的个体饮食专业化，这使得该数据集成为探索野生种群组织之间AA δ ^{13 C 值差异的绝佳数据集。}我们发现AA _NESS谷氨酸、脯氨酸、丝氨酸和甘氨酸以及 AA _{ESS苏氨酸的}δ ¹³ C 值在组织之间存在显着差异，表明组织合成过程中可能存在同位素歧视。相对于骨胶原和肌肉，肝脏中的苏氨酸δ ¹³ C 值较高，这可能表明苏氨酸在糖异生中的分解代谢，肝脏中苏氨酸的δ ¹³ C 值及其糖异生产物甘氨酸和丝氨酸之间的相关性进一步支持了这一解释。这种个体内的同位素变化在组织之间产生了不同的生态解释。对于所分析的 6/10 的海獭个体来说，至少有一种组织表明其依赖于与其他组织不同的初级生产者来源。我们的结果强调了食肉海洋哺乳动物中糖异生的重要性，并表明代谢过程影响 AA _ESS和 AA _NESS δ ¹³ C 值以及多元 AA δ ¹³ C 模式。