Department of Zoology and Entomology, Mammal Research Institute, University of Pretoria, Private Bag X20, Hatfield, 0028, South Africa.
Department of Biological Sciences, Old Dominion University, Norfolk, VA, 23529, USA.
Oecologia. 2020 May;193(1):53-65. doi: 10.1007/s00442-020-04645-5. Epub 2020 Apr 16.
Changes in the nutritional status of free-ranging animals have a strong influence on individual fitness, yet it remains challenging to monitor longitudinally. Nitrogen (δN) and carbon (δC) isotope values measured chronologically along the length of metabolically inert keratinous tissues can be used as a nutritional biomarker to retrospectively reconstruct the foraging ecology and eco-physiology of consumers. We quantitatively describe the physiological effects of fasting on amino acid metabolism using sequentially measured bulk tissue and amino acid δN values along the length of whiskers sampled from free-ranging juvenile, subadults, adult female, and male southern elephant seals (SES; Mirounga leonina) on Marion Island in the Southern Ocean. For both juveniles and adult females, whisker segments representing fasting had significantly higher bulk tissue δN values of 0.6 ± 0.5‰ and 1.3-1.8‰, respectively, in comparison to segments unaffected by fasting. We also found a large increase (2-6‰) in δN values for most glucogenic amino acids and a simultaneous depletion (2-3‰) of alanine in segments reflecting fasting, which enabled us to accurately predict (74%) the nutritional status of our model species. We hypothesize that the glucose-alanine cycle is the mechanism driving the observed depletion of alanine δN values during fasting. We demonstrated that keratinaceous tissues can be used as a longitudinal nutritional biomarker to detect changes in the nitrogen balance of an individual. Moreover, it is evident that physiological factors have an important influence on tissue δN values and can lead to erroneous bulk tissue or amino acid isotope-based reconstructions of foraging habits.
自由放养动物的营养状况变化对个体健康有很大影响，但长期监测仍然具有挑战性。沿代谢惰性角蛋白组织长度测量的氮（δN）和碳（δC）同位素值可用作营养生物标志物，用于追溯性重建消费者的觅食生态和生态生理学。我们使用从南大洋马里恩岛自由放养的幼年、亚成年、成年雌性和雄性南方象海豹（Mirounga leonina）的胡须中沿长度顺序测量的批量组织和氨基酸 δN 值，定量描述了禁食对氨基酸代谢的生理影响。对于幼崽和成年雌性来说，代表禁食的胡须段的总组织 δN 值分别显著升高了 0.6±0.5‰和 1.3-1.8‰，与不受禁食影响的段相比。我们还发现，在反映禁食的段中，大多数生糖氨基酸的 δN 值增加了 2-6‰，而丙氨酸同时减少了 2-3‰，这使我们能够准确预测我们模型物种的营养状况（74%）。我们假设葡萄糖-丙氨酸循环是导致禁食期间丙氨酸 δN 值耗竭的机制。我们证明，角蛋白组织可用作纵向营养生物标志物，以检测个体氮平衡的变化。此外，显然生理因素对组织 δN 值有重要影响，并可能导致基于批量组织或氨基酸同位素的觅食习惯重建出现错误。
