Dietary protein content and digestibility influences discrimination of amino acid nitrogen isotope values in a terrestrial omnivorous mammal

Rationale Ecologists increasingly determine the ?15N values of amino acids (AA) in animal tissue; “source” AA typically exhibit minor variation between diet and consumer, while “trophic” have increased consumers. Thus, trophic-source offsets (i.e., ?15NT-S) reflect trophic position a food web. However, even variations ?15Nsource may influence magnitude offset that represents step, known as discrimination factor TDFT-S). Diet digestibility protein content can bulk tissue, but effects these factors on ?15NT-S TDFT-S mammals are unknown. Methods We fed captive mice (Mus musculus) either (A) low-fat, high-fiber with low, intermediate, or high protein; (B) high-fat, low-fiber low intermediate protein. Mouse muscle dietary were analyzed for tissue using elemental analyzer-isotope ratio mass spectrometry (EA-IRMS), also hydrolyzed into free gas chromatography-combustion-IRMS. Results As increased, ?15NConsumer-Diet slightly declined both experiments; (A); remained same decreased (B). The varied by consistent variables. Conclusions Diets less digestible included more Experiment A than B. result, probably oxidized AA, resulting greater values. similar responses to suggest if samples available, accurately tracks position. If not patterns presented here provide basis interpret Pro-Lys did vary across diets, therefore be reliable omnivores other (e.g., Glu-Phe).