The analysis of (13)C/(12)C ratios in exhaled CO(2): Its advantages and potential application to field research to infer diet, changes in diet over time, and substrate metabolism in birds
Hatch, Kent A
Stable isotopes have long been important tools for plant physiologists and physiological ecologists. Currently, the use of stable isotopes in animal physiology and physiological ecology is gaining more attention and reviews of the topic appear with increasing frequency (Peterson and Fry, 1987; Rundel et al., 1988; Griffiths, 1991; Macko, 1994; Gannes et al., 1997, 1998; Kelly and Finch, 1998; Hobson, 1999; Hobson and Wassenaar, 1999; Kelly, 2000). The most common uses of stable isotopes in ecology are the analyses of 15N/14N to establish trophic levels, food webs (e.g., Fry, 1988; Ambrose, 1991; Hobson and Welch, 1992, 1995; Jarman et al., 1996; Sydeman et al., 1997; Peterson, 1999), dietary analysis and reconstruction (e.g., Handley et al., 1991; Hobson and Sealy, 1991; Angerbjorn et al., 1994; Hobson, 1995; Alexander et al., 1996; Hobson and Sease, 1998). Recently, stable isotopes have been used to discern animal movement patterns (Alisausakas and Ankney, 1992; Hobson and Wassenaar, 1997; Hobson, 1999; Hobson et al., 1999). While hair and feathers are occasionally used, usually tissues such as liver, muscle, and collagen derived from bones are analyzed for stable isotope ratios. This is, of course, rather invasive and usually requires the death of the study animals. Consequently, these techniques are not very useful with rare and endangered species or for mark-recapture studies. The analysis of ^sup 13^C^sup 12^C ratios in exhaled CO2 provides an alternative method that has been little explored by animal physiological ecologists.
In contrast, there is an ample medical literature on ^sup 13^C breath tests. These tests are used both in basic research and in clinical practice. Since little attention has been given to ^sup 13^C breath tests in animal physiological ecology, the purpose of this paper is to: 1) briefly review the existing medical literature, 2) discuss the uses in field research to which ^sup 13^C^sup 12^C analysis of breath can currently be applied, and 3) discuss future directions for research and applications of ^sup 13^C^sup 12^C breath analysis. As others have before us (Gannes et al., 1997), we must extend a word of caution that much work needs to be done in the field of stable isotopes to validate the underlying assumptions.
^sup 13^C^sup 12^C ratios
We extend special thanks to Peter Thomson and Jane McLaren for technical assistance with the mass spectrometry and thanks to C. Richard Tracy, Christopher Gienger, Joan Wright, Ken Nussear, Eric Simandle, Micheal Sears, Denise Jones and Szabolcs Lengyel for their comments and suggestions. During the study KH was supported by a Fulbright Post-doctoral Fellowship through the United States-Israel Educational Foundation. This study was supported by United States-Israel Binational Science Foundation grant number 93-00232. This is paper number 341 of the Mitrani Department for Desert Ecology.
Copyright Society for Integrative and Comparative Biology Feb 2002
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