Insights into amino acid fractionation and incorporation by compound-specific carbon isotope analysis of three-spined sticklebacks

Hesse T, Nachev M, Khaliq S, Jochmann MA, Franke F, Scharsack JP, Kurtz J, Sures B, Schmidt TC

Abstract

Interpretation of stable isotope data is of upmost importance in ecology to build sound models for the study of animal diets, migration patterns and physiology. However, our understanding of stable isotope fractionation and incorporation into consumer tissues is still limited. We therefore measured the delta C-13 values of individual amino acids over time from muscle and liver tissue of three-spined sticklebacks (Gasterosteus aculeatus) on a high protein diet. The delta C-13 values of amino acids in the liver quickly responded to small shifts of under +/- 2.0 parts per thousand in dietary stable isotope compositions on 30-day intervals. We found on average no trophic fractionation in pooled essential (muscle, liver) and non-essential (muscle) amino acids. Negative Delta delta C-13 values of - 0.7 +/- 1.3 parts per thousand were observed for pooled non-essential (liver) amino acids and might indicate biosynthesis from small amounts of dietary lipids. Trophic fractionation of individual amino acids is reported and discussed, including unusual Delta delta C-13 values of over + 4.9 +/- 1.4 parts per thousand for histidine. Arginine and lysine showed the lowest trophic fractionation on individual sampling days and might be useful proxies for dietary sources on short time scales. We suggest further investigations using isotopically enriched materials to facilitate the correct interpretation of ecological field data.