Variation of bone collagen amino acid δ¹³c values in archaeological humans and fauna with different dietary regimes: Developing frameworks of dietary discrimination

Abstract

We present bone collagen amino acid (AA) δ(13)C values for a range of archaeological samples representing four "benchmark" human diet groups (high marine protein consumers, high freshwater protein consumers, terrestrial C(3) consumers, and terrestrial C(4) consumers), a human population with an "unknown" diet, and ruminants. The aim is to establish an interpretive palaeodietary framework for bone collagen AA δ(13)C values, and to assess the extent to which AA δ(13)C values can provide additional dietary information to bulk collagen stable isotope analysis. Results are analyzed to determine the ability of those AAs for which we have a complete set, to discriminate between the diet groups. We show that very strong statistical discrimination is obtained for all interdiet group comparisons. This is often obvious from suitably chosen bivariate plots using δ(113)C values that have been normalized to compensate for interdiet group differences in bulk δ(13)C values. Bi-plots of non-normalized phenylalanine and valine δ(13)C values are useful for distinguishing aquatic diets (marine and freshwater) from terrestrial diets. Our interpretive framework uses multivariate statistics (e.g., discriminant analysis) to optimize the separation of the AA δ(13)C values of the "benchmark"' diet groups, and is capable of accurately assigning external samples to their expected diet groups. With a growing body of AA δ(13)C values, this method is likely to enhance palaeodietary research by allowing the "unknown" diets of populations under investigation to be statistically defined relative to the well-characterized or "known" diets of previously investigated populations.

Comparison of liquid chromatography–isotope ratio mass spectrometry (LC/IRMS) and gas chromatography–combustion–isotope ratio mass spectrometry (GC/C/IRMS) for the determination of collagen amino acid δ13C values for palaeodietary and palaeoecological reconstruction

“…Ser is typically affected by the baseline fluctuation, [12,16] but in this case it consistently elutes after the baseline has stabilised, thereby making peak integration straightforward. Critically, HPLC analyses of the five reference AAs also showed that the LGlu d…”

“…[9] This finding has stimulated the investigation of other proxies to identify the same phenomenon. [8,16] Despite these advances, it is clear that the interpretive frameworks ultimately depend on a firm understanding of the capabilities of the analytical technologies that are used to produce compound-specific data: an area in which surprisingly little comparative work has been devoted, but which this paper aims to address.…”

“…Overall, with the notable exception of Gly, the TFA/IP esters tend to produce comparatively high d values using a mass balance equation that is anchored to the carbon contribution of the constituent AAs of skeletal collagen, as defined by genomic data. [16] Three broad mass balance comparisons of the LC/IRMS and GC/C/IRMS d 13 C (as NACME derivatives) values, and the original values presented in Corr et al, [9] can be considered. First, only the seven AAs common to all three methods are considered: Asp, Hyp, Glu, Gly, Ala, Pro and Phe.…”

“…[10,11,15] Given the promise of AA stable isotope analysis, interpretive frameworks are being developed to synthesise a growing body of compoundspecific isotope data. [8,9,16,17] The gas chromatographycombustion-isotope ratio mass spectrometry (GC/C/IRMS) analysis of skeletal collagen AAs, for instance, has revealed a proxy for the detection of marine protein consumption, where differences in the d 13 C values between the AAs glycine (Gly) and phenylalanine (Phe) are substantially greater for consumers of marine foods than for those consuming primarily terrestrial-based resources (Δ 13 C Glycine-Phenylalanine ). [9] This finding has stimulated the investigation of other proxies to identify the same phenomenon.…”

Analysis of collagen preservation in bones recovered in archaeological contexts using NIR Hyperspectral Imaging

“…These analyses include the Zooarchaeology by Mass Spectrometry (ZooMS) technique for taxonomic identification of even very small bone particles by comparison of the amino acid groupings contained in bone collagen ([5]- [6]), radiocarbon (AMS) dating of bone from archaeological contexts ( [7]- [8]) and stable isotopic analyses to reconstruct past human and animal diets ( [9]- [10]). …”