Diet and Climate Experiments on Nitrogen Isotope Ratios of Rats

Controlled Diet and Climate Experiments on Nitrogen Isotope Ratios of Rats 

Nitrogen isotope ratios ( N/ N) inerease from plants to herbivores to eami-vores and ean be used to estimate the degree of camivory in human diets. Some field studies observe a greater differenee in 5 N between trophie levels in dry, hot habitats than in wet, cool ones. Two hypotheses have been proposed to explain this variation in difference in 8 N between trophic levels. (1) Elevated excretion of -depleted urea in heat/water-stressed animals (2) recycling of nitrogen on protein-deficient diets. Both predict increased diet-tissue 8 N difference under stress. 

Biogeochemical Approaches to Paleodietary Analysis, edited by Ambrose and Katzenberg. 

Decreases in muscle and increases in hair and collagen 6 N with age were observed in litters raised on 20% protein. These results provide partial support for the hypothesis of a relationship between and age. 

The increase in diet-tissue spacing has been proposed to be caused by the effects of water and heat stress on urinary nitrogen excretion. The model has been described in detail previously (Ambrose 1991) and will be briefly summarized here Nitrogen is excreted mainly as urinary urea. Its 6 N value is substantially (2-5%o) more negative than that of the diet (Steele Daniel 1978 Yoneyama et al. 1983). Under heat and water stress the concentration 

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Ambrose, S.H. 2000. Controlled diet and climate experiments on nitrogen isotope ratios of rat bone collagen, hair and muscle. In Biogeochemical Approaches to Paleodietary Analysis, S.H. Ambrose, and M.A. Katzenberg (eds.), pp. 243-259. New York Kluwer Academic/Plenum. 

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