Dietary protein influences the rate of 15N incorporation in blood cells and plasma of Yellow-vented bulbuls (Pycnonotus xanthopygos).
The rate at which an animal's tissues incorporate the isotopic composition of food determines the time window during which ecologists can discern diet changes. We investigated the effect of protein content in the diet on the incorporation rate of (15)N into the plasma proteins and blood cells of Yellow-vented bulbuls (Pycnonotus xanthopygos). Using model comparison analyses, we found that one-compartment models described incorporation data better than two-compartment models. Dietary protein content had a significant effect on the residence time of (15)N in plasma proteins and blood cells. The diet with the highest protein content led to a (15)N retention time of 21 and 5 days for cells and plasma, respectively. In contrast, average (15)N retention time in the cells and plasma of birds fed on the diet with the lowest protein was 31 and 7 days, respectively. The isotopic discrimination factor Delta(15)N=delta(15)N(tissues)-delta(15)N(diet) was also dependent on dietary protein content, and was lowest in birds fed the diet with the highest protein content. Blood, plasma and excreta were enriched in (15)N relative to diet. In contrast, ureteral urine was either significantly depleted of (15)N in birds fed the diet with the lowest protein content or did not differ in delta(15)N from the diets with the intermediate and high protein content. Thus, isotopic incorporation rates and tissue-to-diet discrimination factors cannot be considered fixed, as they depend on diet composition.
Tsahar
Ella
E
Department of Biology, Technion - Israel Institute of Technology, Haifa 32000, Israel. elat@techunix.technion.ac.il
Wolf
Nathan
N
Izhaki
Ido
I
Arad
Zeev
Z
Del Rio
Carlos Martínez
CM
D000818:Animals; D001773:Blood Cells / Q000378:metabolism*; D004044:Dietary Proteins / Q000032:analysis / Q000378:metabolism*; D007700:Kinetics; D009587:Nitrogen Isotopes; D046109:Passeriformes / Q000097:blood*; D013997:Time Factors
D004044:Dietary Proteins; D009587:Nitrogen Isotopes