Michael J. Gravett and Professor Kent Hatch, Integrative Biology
Stable isotope ratios have been used for a variety of purposes in the biological sciences. These ratios have been used by plant ecologists to asses the photosynthetic mode, to measure water balance, and to trace nitrogen sources (Gannes, 1997). They have been used by animal ecologists to determine trophic relationships in food webs, to discriminate between animals that live in different biomes, to trace migratory animals, to follow nutrients through the body, and to undertake dietary reconstruction of both current and extinct species (Bearhop, 2002).
Most stable isotope studies to date have measured the isotope ratios in tissues. However, assumptions upon which whole tissue analyses are based are rarely valid (Gannes et al. 1997, 1998). When a mixture, such as a whole tissue, is isotopically analyzed the effects of the ratios within its components are combined into one measurement. Consequently, information on the isotope ratios in the various proteins, lipids, and carbohydrates found in the tissue are lost. This is a problem because dietary intake can affect the isotope ratios of each of these components differently. As a further complication, nutrients obtained from internal stores may also affect isotope ratios in selective tissue components (Hobson & Clark 1993). These and other problems have demonstrated the need for controlled studies to isotopically analyze tissue components rather than whole tissues.
The purpose of this project was to measure the effects of dietary stress on the carbon and nitrogen isotope ratios of hemoglobin, serum albumin, and the plasma globulin proteins. Originally we were to make these measurements on alpaca blood from previous experiments. However, because there was not enough blood in storage a new experiment was designed and carried out during the summer of 2004. This delayed the process of protein purification and isotope measurements. Additionally the protein purification was not as straight forward as the literature implied and new methods had to be developed to obtain the purity that was needed. Because of these complications the project has not yet been completed. During this spring and summer proteins will be purified from the remaining blood samples. These samples will then be isotopically analyzed using our isotope ratio mass-spectrometer.
This project has been an important growing experience for me. I have learned how to think like a scientist, how to design an experiment, how to lead and oversee a group of researchers, and how to interpret data. I am looking forward to publishing the results of this project at the end of the summer.
References
- Bearhop, S., S. Waldron, S.C. Votier, R.W. Furness. 2002. Factors that influence assimilation rates and fractionation of nitrogen and carbon stable isotopes in avian blood and feathers. Physiological and Biochemical Zoology. 75(5): 451-458.
- Gannes, L.Z., D.M. O’Brien, and C.M. del Rio. 1997. Stable isotopes in animal ecology: assumptions, caveats, and a call for more laboratory experiments. Ecology. 78: 1271- 1276.
- Gannes, L.Z., C.M. del Rio and P. Koch. 1998. Natural abundance variations in stable isotopes and their potential uses in animal physiological ecology. Comparative Biochemistry and Physiology A-Molecular & Integrative physiology. 119 (3): 725-737.
- Hobson, K.A., R.T. Alisauskas, R.G. Clark. 1993. Stable-nitrogen isotope enrichment in avian tissues due to fasting and nutritional stress: implications for isotopic analyses of diet. The Condor. 95: 388-394.