We develop and test a model to predict the geographic region-oforigin of humans based on the stable isotope composition of their scalp hair. This model incorporates exchangeable and nonexchangeable hydrogen and oxygen atoms in amino acids to predict the ␦ 2 H and ␦ 18 O values of scalp hair (primarily keratin). We evaluated model predictions with stable isotope analyses of human hair from 65 cities across the United States. The model, which predicts hair isotopic composition as a function of drinking water, bulk diet, and dietary protein isotope ratios, explains >85% of the observed variation and reproduces the observed slopes relating the isotopic composition of hair samples to that of local drinking water. Based on the geographical distributions of the isotope ratios of tap waters and the assumption of a ''continental supermarket'' dietary input, we constructed maps of the expected average H and O isotope ratios in human hair across the contiguous 48 states. Applications of this model and these observations are extensive and include detection of dietary information, reconstruction of historic movements of individuals, and provision of regionof-origin information for unidentified human remains. stable isotopes ͉ water ͉ anthropology ͉ forensics ͉ meteoric water T he carbon (␦ 13 C), nitrogen (␦ 15 N), and sulfur (␦ 34 S) isotope ratios of humans, other animals, and microbes are strongly correlated with the isotope ratios of their dietary inputs (1-5). The adage ''You are what you eat'' reflects the observation that there are limited differences (Յ1‰) between heterotrophic organisms and their diet in either the ␦ 13 C or ␦ 34 S values (6-8). These small isotopic differences arise because of fractionation events during metabolism; they also reflect that diet-derived carbon and sulfur are the only input sources into most heterotrophs. Although there are larger ''spacing'' differences in ␦ 15 N values (Ϸ3‰) between an organism and its dietary source (9), the isotopic relationships between organism and diet persist. ␦ 13 C, ␦ 15 N, and ␦ 34 S values provide limited geographic-based information about the origins of a food source. Hydrogen (␦ 2 H) and oxygen (␦ 18 O) isotope ratios of organic matter are more useful, because ␦ 2 H and ␦ 18 O values of precipitation and tap waters vary along geographic gradients (10, 11).Although differences in the ␦ 2 H and ␦ 18 O values of scalp hair have been noted in humans (12), less is known about dietorganism patterns of ␦ 2 H and ␦ 18 O values. Four potential sources can be important: dietary organic molecules, dietary waters, drinking waters, and atmospheric diatomic oxygen. Hobson et al.(13) provided evidence that ␦ 2 H values of drinking water were incorporated into different proteinaceous tissues of quail, although no mechanistic basis was proposed for this relationship. The ␦ 2 H values of bird feathers and butterfly wings (both are largely keratin) and water in the region in which the tissue was produced are highly correlated (14, 15). showed that Ϸ70% of the oxygen and Ϸ...

The reaction progress variable is applied to stable isotope turnover of biological tissues. This approach has the advantage of readily determining whether more than one isotope turnover pool is present; in addition, the normalization process inherent to the model means that multiple experiments can be considered together although the initial and final isotope compositions are different. Consideration of multiple isotope turnover pools allows calculation of diet histories of animals using a time sequence of isotope measurements along with isotope turnover pools. The delayed release of blood cells from bone marrow during a diet turnover experiment can be quantified using this approach. Turnover pools can also be corrected for increasing mass during an experiment, such as when the animals are actively growing. Previous growth models have been for exponential growth; the approach here can be used for several different growth models.

No abstract

We used stable isotopes of C in breath, blood, feces and feathers to identify intra-individual changes in diet and the timescale of diet changes in free-living songbirds at a stopover site. Because accurate interpretation of differences between the delta13C of breath, plasma, and red blood cells (RBCs) relative to diet requires knowing the turnover rate of C within them, we determined the rate of change of C in breath, plasma and RBCs for yellow-rumped warblers (Dendroica coronata). Half-lives of C in breath, plasma, and RBCs were 4.4+/-2.1 h, 24.8+/-12.3 h and 10.9+/-3.2 days, respectively, for yellow-rumped warblers. delta13C of breath, plasma, RBCs and feces from wild-caught golden-crowned kinglets (Regulus satrapa), ruby-crowned kinglets (R. calendula) and gray catbirds (Dumetella carolinensis) indicated that they had maintained an isotopically consistent diet for an extended period of time. However, delta13C of breath and plasma indicated that white-throated sparrows (Zonotrichia albicollis) had recently expanded their diet to include a C4 dietary component. Likewise, delta13C of breath, plasma, RBCs and feces indicated that some wild-caught yellow-rumped warblers had consumed foods with a more enriched protein signature prior to their arrival on Block Island, and since arrival, they had consumed mostly northern bayberry (Myrica pensylvanica). Therefore, comparisons of the delta13C of breath, plasma, RBCs, feces and feathers from individual songbirds can indicate changes in diet and provide an estimate of the timescale of the diet change.