The influence of diet on the distribution of nitrogen isotopes in animals was investigated by analyzing animals grown in the laboratory on diets of constant nitrogen isotopic composition. 
The isotopic composition of the nitrogen in an animal reflects the nitrogen isotopic composition of its diet. The δ^(15)N values of the whole bodies of animals are usually more positive than those of their diets. Different individuals of a species raised on the same diet can have significantly different δ^(15)N values. The variability of the relationship between the δ^(15)N values of animals and their diets is greater for different species raised on the same diet than for the same species raised on different diets. Different tissues of mice are also enriched in ^(15)N relative to the diet, with the difference between the δ^(15)N values of a tissue and the diet depending on both the kind of tissue and the diet involved. The δ^(15)N values of collagen and chitin, biochemical components that are often preserved in fossil animal remains, are also related to the δ^(15)N value of the diet. 
The dependence of the δ^(15)N values of whole animals and their tissues and biochemical components on the δ^(15)N value of diet indicates that the isotopic composition of animal nitrogen can be used to obtain information about an animal's diet if its potential food sources had different δ^(15)N values. The nitrogen isotopic method of dietary analysis probably can be used to estimate the relative use of legumes vs non-legumes or of aquatic vs terrestrial organisms as food sources for extant and fossil animals. However, the method probably will not be applicable in those modern ecosystems in which the use of chemical fertilizers has influenced the distribution of nitrogen isotopes in food sources. 
The isotopic method of dietary analysis was used to reconstruct changes in the diet of the human population that occupied the Tehuacan Valley of Mexico over a 7000 yr span. Variations in the δ^(15)C and δ^(15)N values of bone collagen suggest that C_4 and/or CAM plants (presumably mostly corn) and legumes (presumably mostly beans) were introduced into the diet much earlier than suggested by conventional archaeological analysis.

Influence of Diet On the Distribtion of Nitrogen Isotopes in Animals

In contexts where human remains are scarce, poorly preserved, or otherwise unavailable for stable isotope-based paleodietary reconstruction, dog bone collagen as well as other tissues may provide a suitable proxy material for addressing questions relating to human dietary practices. Inferences drawn from applications of this “canine surrogacy approach” (CSA) must be made with caution to ensure the accuracy and transparency of conclusions. This paper shows that CSA applications are essentially analogical inferences which can be divided into two groups that provide specific types of information and may require different levels of substantiation. A framework of three categories of factors is outlined to aid in establishing positive, negative, and neutral elements of comparison of dog and human diets. CSA applications may benefit from explicitly detailing the type and nature of the analogical reasoning employed and from providing a systematic assessment of the degree to which stable isotope values of dogs and humans under comparison are thought to be like, unlike, or of unknown likeness.

Dogs as Analogs in Stable Isotope-Based Human Paleodietary Reconstructions: A Review and Considerations for Future Use

The spread of agriculture is an important topic of archaeological research, but relatively few studies address the drivers behind the spread of specific species empirically. Here we use published isotopic data to consider whether the millets spread from their putative domestication centre in the East to western Eurasia for use as a staple food. We show that the consumption of significant quantities of millet was both far more sporadic than the earliest appearance of millet might suggest and delayed. This is not to say that millet was not consumed, rather that any consumption was below the level of isotopic detectability, and thus millet cannot generally be considered a staple. Nevertheless, individuals who regularly consumed millet occur both as typical members of their population and as unusual individuals. The reasons for this pattern open up new questions about, and avenues of research into, the spread of agriculture.

Why move starchy cereals? A review of the isotopic evidence for prehistoric millet consumption across Eurasia

Background 
Nitrogen isotope analysis of bone collagen has been used to reconstruct the breastfeeding practices of archaeological human populations. However, weaning ages have been estimated subjectively because of a lack of both information on subadult bone collagen turnover rates and appropriate analytical models.


Methodology 
Temporal changes in human subadult bone collagen turnover rates were estimated from data on tissue-level bone metabolism reported in previous studies. A model for reconstructing precise weaning ages was then developed using a framework of approximate Bayesian computation and incorporating the estimated turnover rates. The model is presented as a new open source R package, WARN (Weaning Age Reconstruction with Nitrogen isotope analysis), which computes the age at the start and end of weaning, 15N-enrichment through maternal to infant tissue, and value of collagen synthesized entirely from weaning foods with their posterior probabilities. The model was applied to 39 previously reported Holocene skeletal populations from around the world, and the results were compared with weaning ages observed in ethnographic studies.


Conclusions 
There were no significant differences in the age at the end of weaning between the archaeological (2.80±1.32 years) and ethnographic populations. By comparing archaeological populations, it appears that weaning ages did not differ with the type of subsistence practiced (i.e., hunting–gathering or not). Most of -enrichment (2.44±0.90‰) was consistent with biologically valid values. The nitrogen isotope ratios of subadults after the weaning process were lower than those of adults in most of the archaeological populations (−0.48±0.61‰), and this depletion was greater in non-hunter–gatherer populations. Our results suggest that the breastfeeding period in humans had already been shortened by the early Holocene compared with those in extant great apes.

/pdf/quantitative-reconstruction-of-weaning-ages-in-11o3jav7zv.pdf

Quantitative reconstruction of weaning ages in archaeological human populations using bone collagen nitrogen isotope ratios and approximate Bayesian computation.

Hunter–gatherer foraging ranges, migrations, and travel in the middle Holocene Baikal region of Siberia: Insights from carbon and nitrogen stable isotope signatures

We analyzed stable carbon and nitrogen isotope ratios in a sample of human and nonhuman mammal bones excavated from the Yoshigo and Inariyama shell mounds of the Late-Final Jomon pe- riods in Aichi Prefecture, Japan, with a view to determining individual dietary differences. To inves- tigate possible reasons for the dietary variations identified, we related isotope ratios to sex and tooth ablation patterns. At both sites, large intra-site variations in δ 13 C and δ 15 N values were found, com- pared with other Jomon populations previously studied, suggesting higher than usual levels of dietary variability, and at both sites there was a positive correlation between δ 13 C and δ 15 N values. The diet of the Jomon people at both these sites had two main protein sources: marine (marine finfish and shell- fish) and terrestrial (C3 plants and terrestrial mammals) protein. The intra-site variability is probably explained by consumption of these resources in different proportions. Analysis of the Yoshigo shell mound data indicated that sex is one of the factors determining dietary difference. It was also found that individual differences in diet in Yoshigo males are greater than in females. This pattern was re- peated in the Inariyama shell mound data. Dietary differences were found to be related to ritual tooth ablation characteristics, particularly in males. At Inariyama, type 4I ritual tooth ablation was associated with comparatively greater dependency on terrestrial resources, while type 2C tooth ablation was as- sociated with greater dependency on marine resources. This may indicate that type 4I males engaged predominantly in hunting, and type 2C males in fishing, as a means of food acquisition. These results are possibly the earliest evidence of occupational differentiation in the Jomon people.

/pdf/variability-in-stable-isotope-ratios-in-two-late-final-jomon-dsguzx45un.pdf

Variability in stable isotope ratios in two Late-Final Jomon communities in the Tokai coastal region and its relationship with sex and ritual tooth ablation

江戸時代は，急激な人口増加とその後の人口安定，また陸・海路による交易網の発達によって特徴づけられ，コメや野菜や魚介類を主要な食物としていたと言われる。そのような江戸時代の人々の食性を，遺跡から出土した人骨を用いて実証しようとするのが本研究である。伏見城跡遺跡（京都市）より出土した江戸時代人骨および動物骨からコラーゲンを抽出して，炭素および窒素の安定同位体比を測定した。合計で27個体（男性9個体，女性12個体，子ども6個体）の人骨を分析に用いた。それにより，伏見江戸時代人の食性，その性差を検討することを目的とした。江戸時代の伏見の人々は，タンパク質源を淡水魚類に強く依存した食生活，もしくは陸上生態系から得られるC3植物と海産あるいは淡水魚類などを主たるタンパク質源とする食生活を送っていた可能性を示した。江戸時代の都市では，食生活が米，野菜，魚介類からなり，アワやヒエ，キビなどC4植物の消費が少ないとする古記録を考慮に入れると，後者の食生活像が支持される。また，男性の炭素同位体比は女性よりも高く，より多くの海産魚類や貝類などを摂取していた可能性がある。また，年齢が上がると子どもの窒素同位体比は下がる傾向があり，これは母乳の摂取と離乳の開始に関連していると考えられる。

Takeyuki Ikarashi

Papers

Variability in stable isotope ratios in two Late-Final Jomon communities in the Tokai coastal region and its relationship with sex and ritual tooth ablation

Stable Isotope Analysis on Human Skeletal Remains from the Edo-period Fushimi Castle Site in Japan