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.

A semimechanistic model has recently been proposed to explain observed correlations between the H and O isotopic composition of hair from modern residents of the USA and the isotopic composition of drinking water, but the applicability of this model to hair from non-USA and preglobalization populations is unknown. Here we test the model against data from hair samples collected during the 1930s-1950s from populations of five continents. Although C and N isotopes confirm that the samples represent a much larger range of dietary "space" than the modern USA residents, the model is able to reproduce the observed delta(2)H and delta(18)O values given reasonable adjustments to 2 model parameters: the fraction of dietary intake derived from locally produced foods and the fraction of keratin H fixed during the in vivo synthesis of amino acids. The model is most sensitive to the local dietary intake, which appears to constitute between 60% and 80% of diet among the groups sampled. The isotopic data are consistent with a trophic-level effect on protein H isotopes, which we suggest primarily reflects mixing of (2)H-enriched water and (2)H-depleted food H in the body rather than fractionation during biosynthesis. Samples from Inuit groups suggest that humans with marine-dominated diets can be identified on the basis of coupled delta(2)H and delta(18)O values of hair. These results indicate a dual role for H and O isotopic measurements of keratin, including both biological (diet, physiology) and environmental (geographic movement, paleoclimate) reconstruction.

We report isotopic data (delta(2)H, delta(18)O n = 196; delta(13)C, delta(15)N n = 142; delta(34)S n = 85) from human hair and drinking water (delta(2)H, delta(18)O n = 67) collected across China, India, Mongolia, and Pakistan. Hair isotope ratios reflected the large environmental isotopic gradients and dietary differences. Geographic information was recorded in H and O and to a lesser extent, S isotopes. H and O data were entered into a recently developed model describing the relationship between the H and O isotope composition of human hair and drinking water in modern USA and pre-globalized populations. This has anthropological and forensic applications including reconstructing environment and diet in modern and ancient human hair. However, it has not been applied to a modern population outside of the USA, where we expect different diet. Relationships between H and O isotope ratios in drinking water and hair of modern human populations in Asia were different to both modern USA and pre-globalized populations. However, the Asian dataset was closer to the modern USA than to pre-globalized populations. Model parameters suggested slightly higher consumption of locally produced foods in our sampled population than modern USA residents, but lower than pre-globalized populations. The degree of in vivo amino acid synthesis was comparable to both the modern USA and pre-globalized populations. C isotope ratios reflected the predominantly C(3)-based regional agriculture and C(4) consumption in northern China. C, N, and S isotope ratios supported marine food consumption in some coastal locales. N isotope ratios suggested a relatively low consumption of animal-derived products compared to western populations.

During fall migration many songbirds switch from consuming primarily insects to consuming mostly fruit. Fruits with more carbohydrates and less protein may be sufficient to rebuild expended fat stores, but such fruits may be inadequate to replace catabolized protein. We manipulated the concentrations and isotopic signatures of macronutrients in diets fed to birds to study the effects of diet quality on metabolic routing of dietary nutrients. We estimated that approximately 45% and 75%, respectively, of the carbon in proteinaceous tissue of birds switched to high- or low-protein diets came from nonprotein dietary sources. In contrast, we estimated that approximately 100% and 20%-80%, respectively, of the nitrogen in proteinaceous tissues of birds switched to high- or low-protein diets was attributable to dietary protein. Thus, the routing and assimilation of dietary carbon and nitrogen differed depending on diet composition. As a result, delta (15)N of tissues collected from wild animals that consume high-quality diets may reliably indicate the dietary protein source, whereas delta (13)C of these same tissues is likely the product of metabolic routing of carbon from several macronutrients. These results have implications for how isotopic discrimination is best estimated and how we can study macronutrient routing in wild animals.

We calculated the fraction of exchangeable hydrogen atoms in proteinaceous materials commonly analyzed for stable isotopic composition related to the region-of-origin of an animal. These included several types of alpha- and beta-keratin, and muscle tissue. We find that the fraction of H atoms in keratin available for exchange at a biologically relevant temperature (25 degrees C) averaged 9% across a range of ground organic materials, but was as high as approximately 17% in cut hair; muscle tissue has approximately 12% exchangeable H atoms. Under most analysis conditions, the difference in exchangeable fractions due to physical sample processing has a minimal effect on the calculated delta2H values of the non-exchangeable H atoms within a keratin-containing tissue (<2 per thousand). However, extreme mismatches between sample and reference material types could affect delta2H values.