Chicken and Egg: Testing the Carbon Isotopic Effects of Carnivory and Herbivory

Abstract

13C bioapatite-diet spacing, and not that of Δ 13C collagen-diet . KEYWORDS: BIOMINERAL, ISOTOPE ANALYSIS, PALAEODIET, ISOTOPE ECOLOGY INTRODUCTIONThe relationship between the carbon and nitrogen isotope composition of an individual's diet and their body tissues is now frequently employed as a method of dietary analysis in several different research fields, including ecology, archaeology and physiology (Gannes et al. 1998; Lee-Thorp 2008;Boecklen et al. 2011). The underlying basis of such work is that there is an isotopic 'fine structure' within the biosphere due to fractionation during natural processes, which results in isotopic differences between food types. An individual's diet can thus be inferred from the isotopic signature, which is transferred to and retained in the body during the absorption and incorporation of food.The interpretation of diet is predicated on understanding and therefore accounting for any isotopic fractionation resulting from the incorporation of diet into body tissues. Over the decades, there have been a number of empirical studies aimed at elucidating isotopic fractionation during the body's metabolism, yet some observed patterns remain puzzling. One such is the offset between the carbon isotopic values of the biomineral and protein components of bone. This study *Received 21 January 2016; accepted 24 March 2016 †Corresponding author: email tco21@cam.ac.uk Archaeometry 59, 2 (2017Archaeometry 59, 2 ( ) 302-315 doi: 10.1111 This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. Krueger and Sullivan (1984) found a Δ 13 C ap-coll spacing of +7‰ for modern herbivores (n = 20), and +3-4‰ for modern carnivores (n = 40). Their analyses of over 200 archaeological humans showed that the majority had Δ 13 C ap-coll spacings of +3 to +7‰, as would be predicted for omnivores. In modern southern African wild fauna, Lee-Thorp et al. (1989) found that the Δ 13 C ap-coll was +6.8 ± 1.4‰ for herbivores (n = 67) and +4.3 ± 1.0‰ for carnivores (n = 49), with both groups having similar bioapatite δ C ap-coll between herbivores (+7.6 ± 0.5‰, n = 46) and carnivores (+4.8 ± 0.4‰, n = 27). Similar Δ 13 C ap-coll values have been found in a range of other ungulate herbivores (Schoeninger and DeNiro 1982;Nelson et al. 1986;Kellner and Schoeninger 2007). In predominately herbivorous primates, Crowley et al. (2010) observed a mean Δ 13C ap-coll of +5.6‰, with some variability (range of +3.6 to +8.6‰). Ambrose (1993) analysed East African historical human bone, and showed that the Δ 13C ap-coll of pastoralists (Kalenjin, Turkana, Pokot and Dasenech) was +3.8 ± 1.2‰ (n = 8), whereas the Δ 13 C ap-coll of Kikuyu farmers was +5.5 ± 0.5‰ (n = 16), supporting the theory that those humans with a diet high in animal protein have a smaller spacing between their collagen and bioapatite δ 13 C than predominantly plant-eating farmers. Although based on a limited number of...

Within trophic level shifts in collagen–carbonate stable carbon isotope spacing are propagated by diet and digestive physiology in large mammal herbivores

“…Empirical data for compound‐specific isotope compositions of Savannah plants are needed. More so, however, controlled experiments like those of O'Connell and Hedges (), which explicitly test for diet‐linked physiological effects on spacing, are needed. The drawback is that such experiments are necessarily long term, given the time needed for bone to be remodeled and become equilibrated with an experimental diet/s.…”

“…To compare relationships between δ 13 C carbonate and δ 13 C collagen across trophic groups (herbivores, carnivores, omnivores, and primates), we used reduced major axis (RMA) regression models. We treated δ 13 C carbonate as the “response” ( y ‐axis) variable to be consistent with other approaches in the literature (e.g., Lee‐Thorp et al., ), and because previous studies have predicted that physiology mainly affects δ 13 C carbonate rather than δ 13 C collagen (Hedges, ; O'Connell & Hedges, ; Passey et al., ). These regression models were applied to each trophic group (herbivores, carnivores, omnivores, and primates) separately, using data for all individuals, regardless of taxon, for which both δ 13 C carbonate and δ 13 C collagen data are available.…”

“…In particular, data for rodents were derived from animals fed complex pelleted diets, which are expected to be isotopically heterogeneous and could easily account for the different diet‐δ 13 C carbonate and δ 13 C collagen –δ 13 C carbonate relationships observed in rodents compared to experiments where animals had access to more natural diets (see also Codron, Sponheimer, et al., ). A recent experimental study found that Δ 13 C protein‐carbonate spacing differed within a single bird species (hens) fed plant‐based (large spacing), meat‐based (smaller spacing), or omnivorous (intermediate spacing) diets (O'Connell & Hedges, ). Although these most recent experiments are consistent with a diet‐based explanation for patterns in δ 13 C collagen –δ 13 C carbonate relationships, the authors noted that only hens on herbivorous diets reached isotopic equilibrium with their foods and so conclusions based on their estimates of spacing for meat based and omnivorous diets were treated with caution.…”

“…Lipids in particular are 13 C-depleted relative to other biochemical carbon sources (Tieszen, Boutton, Tesdahl, & Slade, 1983), and therefore, a lipid-rich diet is expected to lead to low δ 13 C carbonate values. This observation has often been invoked to explain why Δ 13 C collagen-carbonate spacing in carnivores is only ~4 ‰, much lower than in herbivores, as carnivores consume a greater proportion of dietary lipids (Krueger & Sullivan, 1984;Lee-Thorp et al, 1989;O'Connell & Hedges, 2017). Accordingly, Δ 13 C collagen-carbonate spacing has been used to infer trophic levels of fossil animals, including humans, recovered from sites where both materials retain lifetime isotopic compositions (e.g., Bocherens et al, 2017;Clementz et al, 2009).…”

Cracking the egg: the use of modern and fossil eggs for ecological, environmental and biological interpretation

“…They showed that it is possible to reconstruct diet of these penguins when the right discrimination factors are taken into account; without their experiments, estimations of past environments and ecologies of these penguins would have been grossly misinformed. This work on the isotope systematics has laid the groundwork for other studies that use modern eggshells and egg membranes to make ecological, environmental and dietary inferences in water birds [ 45 , 46 ], chickens [ 47 ] and penguins [ 48 ], illustrating the use of eggs for modern ecology and conservation.…”