科研之友
微信
新浪微博
Facebook
分享链接
摘要
Stable nitrogen isotopic composition of amino acids (N-15(AA)) has recently been employed as a powerful tool in ecological food web studies, particularly for estimating the trophic position (TP) of animal species in food webs. However, the validity of these estimates depends on the consistency of the trophic discrimination factor (TDF; = N-15(AA) at each shift of trophic level) among a suite of amino acids within the tissues of consumer species. In this study, we determined the TDF values of amino acids in tadpoles (the Japanese toad, Bufo japonicus) reared exclusively on one of three diets that differed in nutritional quality. The diets were commercial fish-food pellets (plant and animal biomass), bloodworms (animal biomass), and boiled white rice (plant carbohydrate), representing a balanced, protein-rich, and protein-poor diet, respectively. The TDF values of two source amino acids (Src-AAs), methionine and phenylalanine, were close to zero (0.3-0.5 parts per thousand) among the three diets, typifying the values reported in the literature (similar to 0.5 parts per thousand and similar to 0.4 parts per thousand, respectively). However, TDF values of trophic amino acids (Tr-AAs) including alanine, valine, leucine, isoleucine, and glutamic acid varied by diet: for example, the glutamic acid TDF was similar to the standard value (similar to 8.0 parts per thousand) when tadpoles were fed either the commercial pellets (8.0 parts per thousand) or bloodworms (7.9 parts per thousand), but when they were fed boiled rice, the TDF was significantly reduced (0.6 parts per thousand). These results suggest that a profound lack of dietary protein may alter the TDF values of glutamic acid (and other Tr-AAs and glycine) within consumer species, but not the two Src-AAs (i.e., methionine and phenylalanine). Knowledge of how a nutritionally poor diet can influence the TDF of Tr- and Src-AAs will allow amino acid isotopic analyses to better estimate TP among free-roaming animals.
- 出版日期2015-5
