Hair δ13C Research Articles

Using the natural abundance of nitrogen isotopes to identify cattle with greater efficiency in protein-limiting diets

The difficulty in selecting cattle for higher feed and nitrogen use efficiency (NUE) is an important factor contributing to poor growth and reproductive performance in dry-tropics rangelands. Therefore, the objectives were to examine the cattle variation in retaining nitrogen in a protein-deficient diet and the natural abundance of stable isotopes in body tissues as a practical alternative for the detection of more efficient cattle. In experiment 1, feed efficiency parameters were determined in 89 Brahman steers fed a protein-limiting diet for 70 days, followed by 7 days in metabolism crates for total collection of urine and faeces and calculation of nitrogen retention and NUE. The diet-animal fractionation of nitrogen isotopes (Δ15N) was quantified in tail hair and plasma proteins using isotope-ratio MS. There was a large variation in growth performance, feed efficiency and nitrogen losses among steers. Quantifying Δ15N in tail hair (Δ15Ntail hair) resulted in stronger correlations with feed efficiency and nitrogen metabolism parameters than when quantified in plasma proteins. Δ15Ntail hair was positively correlated with nitrogen losses in urine (r = 0.31, P < 0.01) and faeces (r = 0.25, P = 0.04), leading to a negative correlation with NUE (r = −0.40, P < 0.01). The group of steers with lower Δ15Ntail hair had greater feed efficiency, lower nitrogen losses, and greater NUE. In experiment 2, for evaluation of isotope fraction as a predictor of reproductive performance, 630 Brahman-crossed cows were classified for reproductive performance for 2 years. From this group, 25 cows with poor reproductive performance and 25 cows with good reproductive performance were selected. Tail hair representing 7 months of growth were segmented and analysed for carbon (δ13C) and nitrogen (δ15N) isotope enrichment. Reproductive performance was not associated with diet selection, as there was no difference in tail hair δ13C between groups. However, more productive cows had lower (P < 0.05) tail hair δ15N during the dry season, indicating differences in N metabolism and possibly lower N losses. In addition, cows with better reproductive performance and, therefore, greater nutrient demands, had similar body condition scores and a tendency (P = 0.09) for higher live weight at the end of the trial. In conclusion, the findings of the present study confirm that nitrogen isotope fractionation in tail hair can be used as a predictor of nitrogen losses, NUE, and reproductive performance of Brahman cattle on low-protein diets.

Diversity and Diet Differences of Small Mammals in Commensal Habitats

The stability of diversity of syntopic (inhabiting the same habitat in the same time) small mammals in commensal habitats, such as farmsteads and kitchen gardens, and, as a proxy of their diet, their isotopic niches, was investigated in Lithuania in 2019–2020. We tested whether the separation of species corresponds to the trophic guilds, whether their diets are related to possibilities of getting additional food from humans, and whether their diets are subject to seasonal trends. We analyzed diversity, dominance and distribution of hair δ13C and δ15N values. Diversity and dominance was not stable and differed according to human influence. The highest small mammal species richness occurred in commensal habitats that provided additional food. The degree of separation of species was higher in homestead habitats than in kitchen gardens, where a 1.27% to 35.97% overlap of isotopic niches was observed between pairs of species. Temporal changes in δ13C and δ15N values in the hair of the mammals were not equally expressed in different species. The isotopic overlap may depend on dietary plasticity, minimizing interspecific competition and allowing co-existence of syntopic species. Thus, small mammal trophic ecology is likely related to intensity of agricultural activities in the limited space of commensal habitats.

Validating the use of bulk tissue stable isotope and amino acid δ15N values measured in molted hair and epidermis of elephant seals to assess temporal foraging niche specialization

The degree of dietary generalization versus specialization exhibited by populations can impact their ability to respond to changing environmental conditions. Naturally shed hair and epidermis are easily collected and may provide a suitable substrate for stable isotope analysis to assess trophic niche specialization. Whether fasting influences the isotopic composition of molted tissues has not been assessed. Here, we gauged the validity of using carbon (δ13C) and nitrogen (δ15N) isotope analysis of molted hair and the outermost epidermis as proxies to study the foraging ecology of southern elephant seals Mirounga leonina at Marion Island in the southern Indian Ocean. Similarity in both bulk tissue (δ13C and δ15N) and amino acid (δ15N) isotope values of molted tissues and whiskers known to reflect fasting confirmed that physiological changes associated with fasting influenced hair and epidermis isotope values. We recommend caution when using the isotopic composition of molted hair and epidermis to make ecological inferences regarding diet and/or movement. Despite these limitations, molted hair can be used to detect extreme foraging behaviors, which we show using an extensive data set of hair sampled from marked individuals (n = 331) that hauled out on Marion Island during the 2012-2013 annual pelage molt. Other factors, such as ontogenetic shifts in diet and potential environmental (baseline) isotopic variation, also influence hair δ13C and δ15N values, which complicates the use of isotopic data from molted tissues to assess the temporal consistency of an individuals’ isotopic niche.

Evidence for red fox (Vulpes vulpes) exploitation of anthropogenic food sources along an urbanization gradient using stable isotope analysis

As urban areas expand, wildlife show adaptations to urban ecosystems. We tested two hypotheses for urban populations of red fox (Vulpes vulpes (Linnaeus, 1758)) in urban areas: the population pressure hypothesis, which posits that urban foxes make do with suboptimal habitat, and the urban island hypothesis, which presumes that urban areas provide high-quality habitat. We investigated habitat quality by investigating anthropogenic food in fox diets across a rural–urban gradient in Lancaster, Pennsylvania (USA). We used stable carbon isotopes because human food can have a distinct stable carbon isotope signature. We collected fox hair and stomach samples from 21 locations and extracted land use and land cover characteristics within a 100 ha buffer area. We found that higher δ13C values in fox hair were positively correlated with impervious surface cover and developed open spaces, key metrics of urbanization, and negatively associated with agricultural land cover, an indicator of rural habitats. Overall, fox hair δ13C was less related to urbanization and more related to the availability of developed open spaces that provide habitat with vegetation cover and access to nearby food sources. Our results suggest that urban habitats are high quality and support the growing literature revealing that certain species may thrive in urban areas.

Carbon isoscapes of rodent diets in the Great Plains USA deviate from regional gradients in C4 grass abundance due to a preference for C3 plant resources

Diet is an ecological attribute that species may adjust to cope with changing environments and may indicate how a population responds to changes in resource availability. In the Great Plains, plants utilizing the C4 photosynthetic pathway may increase in abundance in the future because of their high tolerance for warm and dry environments, which are projected to increase. How increased C4 abundance will influence grassland food webs remains unknown.Here, we evaluate how rodent diets vary relative to C4 plant biomass at the regional scale of the southern Great Plains in the U.S. We measured δ13C values of hair from 534 individuals of 14 rodent species. Resulting isoscapes of δ13C values were statistically compared to three proxies for local abundance of C4 grasses across the region.Overall, diets of most rodent species were dominated by C3-derived resources with a few species relying on C4 resources. Ordinary least squares linear regressions indicate that proxies for regional abundance of C4 grasses explain very little of the variance in δ13C values in hair for the entire rodent community, however the isoscape of rodent hair δ13C values does broadly correspond to that for δ13C values of soil organic matter. The difference between median δ13C values of granivores and folivores is significantly and highly correlated with SOM δ13C values.Results from this study can be used as a baseline for characterizing dietary shifts in response to environmental change both in the geological past and in the future, and they identify which dietary categories may be most sensitive to future changes in the regional abundance of C4 grasses.

Field-deployable measurements of free-living individuals to determine energy balance: fuel substrate usage through δ13C in breath CO2 and diet through hair δ13C and δ15N values

ABSTRACTCarbon isotopes of breath CO2 vary depending on diet and fuel substrate used. This study examined if exercise-induced δ13C-CO2 changes in substrate utilization were distinguishable from baseline δ13C-CO2 variations in a population with uncontrolled diet, and compared hair isotope values and food logs to develop an isotope model of diet. Study participants included nine women with diverse Body Mass Index (BMI), age, ancestry, exercise history, and diet. Breath samples were collected prior to and up to 12 h after a 5- or 10 K walk/run. Indirect calorimetry was measured with a smartphone-enabled mobile colorimetric device, and a field-deployable isotope analyzer measured breath δ13C-CO2 values. Diet was assessed by food logs and δ13C, δ15N of hair samples. Post-exercise δ13C-CO2 values increased by 0.54 ± 1.09‰ (1 sd, n = 9), implying enhanced carbohydrate burning, while early morning δ13C-CO2 values were lower than daily averages (p = 0.0043), indicating lipid burning during overnight fasting. Although diurnal δ13C-CO2 variation (1.90 ± 0.77‰) and participant baseline range (3.06‰) exceeded exercise-induced variation, temporal patterns distinguished exercise from dietary isotope effects. Hair δ13C and δ15N values were consistent with a new dietary isotope model. Notwithstanding the small number of participants, this study introduces a novel combination of techniques to directly monitor energy balance in free-living individuals.

Small mammal insectivore stable carbon isotope compositions as habitat proxies in a South African savanna ecosystem

Carbon isotope analysis of fossil micromammalian insectivores holds promise for resolving questions about past environments because these animals have restricted home ranges and are generalist feeders. Thus, their diets likely integrate ecological information about local habitats. In this study, we assessed the degree to which carbon isotope compositions of three sympatric shrew species record spatial changes in habitat in a mosaic southern African savanna environment. Sampling sites were located within 2km of one another, and microhabitat conditions ranged from very open (<5% canopy cover) to wooded (~60% canopy cover). We compared shrew hair δ13C values between microhabitat types, and across taxa, in order to test whether these data follow predictable patterns based on local vegetation.Shrew carbon isotope compositions varied with habitat in a predictable manner within our study area. While taxonomy also influenced δ13C values, this was largely due to differences in habitat preferences of individual taxa and the resultant variation in their relative abundance within each environment. Isotopic differences between habitat types were preserved within taxa where taxa occurred in multiple habitats. To complement this modern study, we performed isotopic analysis of the enamel of insect-eating fossil micromammals from the hominin sites Gladysvale and Sterkfontein in the Cradle of Humankind, South Africa. This subset of fossil micromammals consumed primarily C4-derived carbon.

Change of geographical location from Germany (Bavaria) to USA (Arizona) and its effect on H–C–N–S stable isotopes in human hair

To receive information about the duration of a person's stay abroad related to those questions in forensics, stable isotopes of H–C–N–S were analysed in beard hair samples from four young soldiers, who went from Fürstenfeldbruck (Bavaria, Germany) to Phoenix (Arizona, USA) on the same date for their pilot training over a time period of 3 months. All study subjects were almost of the same age, had similar physical constitutions and stayed at the same military bases for the whole study period. However, the results showed considerable individual variabilities. In Arizona, hair δ13C increased by 2.3 ‰ (±0.6) and δ34S decreased by 1.8 ‰ (±1.2). No remarkable shifts of hair δ15N and δ2H were observed. Significant shifts of δ13C or δ34S in the shaved beard hair samples occurred 8 or 9 days after arrival in Arizona, respectively. The time lag to receive the isotope signals in hair due to US diet correspond to the growth period that hair needs to cover the distance of 2–3 mm from its root to the surface of the skin. This implies that isotopic changes due to the consumption of food and drinks were incorporated almost immediately into the hair protein. Consequently, if connected with an isotopic change of the diet, short-term stays for only a few days might be clearly recognizable within the first millimetres of a scalp hair strand which includes the hair roots.

Niche partitioning in sympatric Gorilla and Pan from Cameroon: implications for life history strategies and for reconstructing the evolution of hominin life history.

Factors influencing the hominoid life histories are poorly understood, and little is known about how ecological conditions modulate the pace of their development. Yet our limited understanding of these interactions underpins life history interpretations in extinct hominins. Here we determined the synchronisation of dental mineralization/eruption with brain size in a 20th century museum collection of sympatric Gorilla gorilla and Pan troglodytes from Central Cameroon. Using δ13C and δ15N of individuals’ hair, we assessed whether and how differences in diet and habitat use may have impacted on ape development. The results show that, overall, gorilla hair δ13C and δ15N values are more variable than those of chimpanzees, and that gorillas are consistently lower in δ13C and δ15N compared to chimpanzees. Within a restricted, isotopically-constrained area, gorilla brain development appears delayed relative to dental mineralization/eruption [or dental development is accelerated relative to brains]: only about 87.8% of adult brain size is attained by the time first permanent molars come into occlusion, whereas it is 92.3% in chimpanzees. Even when M1s are already in full functional occlusion, gorilla brains lag behind those of chimpanzee (91% versus 96.4%), relative to tooth development. Both bootstrap analyses and stable isotope results confirm that these results are unlikely due to sampling error. Rather, δ15N values imply that gorillas are not fully weaned (physiologically mature) until well after M1 are in full functional occlusion. In chimpanzees the transition from infant to adult feeding appears (a) more gradual and (b) earlier relative to somatic development. Taken together, the findings are consistent with life history theory that predicts delayed development when non-density dependent mortality is low, i.e. in closed habitats, and with the “risk aversion” hypothesis for frugivorous species as a means to avert starvation. Furthermore, the results highlight the complexity and plasticity of hominoid/hominin development.

Stable Isotope Models of Sugar Intake Using Hair, Red Blood Cells, and Plasma, but Not Fasting Plasma Glucose, Predict Sugar Intake in a Yup’ik Study Population1,2

Objectively measured biomarkers will help to resolve the controversial role of sugar intake in the etiology of obesity and related chronic diseases. We recently validated a dual-isotope model based on RBC carbon (δ13C) and nitrogen (δ15N) isotope ratios that explained a large percentage of the variation in self-reported sugar intake in a Yup’ik study population. Stable isotope ratios can easily be measured from many tissues, including RBCs, plasma, and hair; however, it is not known how isotopic models of sugar intake compare among these tissues. Here, we compared self-reported sugar intake with models based on RBCs, plasma, and hair δ13C and δ15N in Yup’ik people. We also evaluated associations of sugar intake with fasting plasma glucose δ13C. Finally, we evaluated relations between δ13C and δ15N values in hair, plasma, RBCs, and fasting plasma glucose to allow comparison of isotope ratios across tissue types. Models using RBCs, plasma, or hair isotope ratios explained similar amounts of variance in total sugar, added sugar, and sugar-sweetened beverage intake (∼53%, 48%, and 34%, respectively); however, the association with δ13C was strongest for models based on RBCs and hair. There were no associations with fasting plasma glucose δ13C (R2 = 0.03). The δ13C and δ15N values of RBCs, plasma, and hair showed strong, positive correlations; the slopes of these relations did not differ from 1. This study demonstrates that RBC, plasma, and hair isotope ratios predict sugar intake and provides data that will allow comparison of studies using different sample types.

Dietary heterogeneity among Western industrialized countries reflected in the stable isotope ratios of human hair.

Although the globalization of food production is often assumed to result in a homogenization of consumption patterns with a convergence towards a Western style diet, the resources used to make global food products may still be locally produced (glocalization). Stable isotope ratios of human hair can quantify the extent to which residents of industrialized nations have converged on a standardized diet or whether there is persistent heterogeneity and glocalization among countries as a result of different dietary patterns and the use of local food products. Here we report isotopic differences among carbon, nitrogen and sulfur isotope ratios of human hair collected in thirteen Western European countries and in the USA. European hair samples had significantly lower δ13C values (−22.7 to −18.3‰), and significantly higher δ15N (7.8 to 10.3‰) and δ34S (4.8 to 8.3‰) values than samples from the USA (δ13C: −21.9 to −15.0‰, δ15N: 6.7 to 9.9‰, δ34S: −1.2 to 9.9‰). Within Europe, we detected differences in hair δ13C and δ34S values among countries and covariation of isotope ratios with latitude and longitude. This geographic structuring of isotopic data suggests heterogeneity in the food resources used by citizens of industrialized nations and supports the presence of different dietary patterns within Western Europe despite globalization trends. Here we showed the potential of stable isotope analysis as a population-wide tool for dietary screening, particularly as a complement of dietary surveys, that can provide additional information on assimilated macronutrients and independent verification of data obtained by those self-reporting instruments.

Altitudinal gradients of grassland carbon and nitrogen isotope composition are recorded in the hair of grazers

ABSTRACTAim The hair of grazers provides an isotopic record of environmental and nutritional signals. Here, we assess the effect of altitude on the carbon and nitrogen isotope composition of the hair of ruminant grazers and its relation to grassland vegetation, to evaluate the use of hair isotope data for ecosystem reconstruction, animal nutritional ecology and biogeochemical studies in montane environments.Location European Alps.Methods We sampled grassland vegetation (pure C3) and the hair of ruminants along an altitudinal gradient (400–2500 m), and analysed their isotope composition (δ13C and δ15N). Results were compared with published effects of altitude on 13C in C3 plants at the species level and on 15N at the community level. The study was complemented with a comparison of diet and hair isotope composition in ruminants held in confinement.Results δ13C of hair increased (c. 1.1‰ km−1) and δ15N decreased (c. 1.1‰ km−1) with altitude. The same changes occurred in local grassland vegetation, and in regional to global grassland data sets. Offsets between hair and vegetation 13C or 15N (‘diet–hair shift’) were independent of altitude. Sheep (Ovis aries) and cattle (Bos taurus) exhibited a 13C shift near +3‰, but that of goats (Capra hircus) was larger (+4.2‰) in alpine environments and in confinement. The diet–hair shift for 15N was more variable (+2.1 to +3.6‰).Main conclusions Grazer hair provides a faithful spatially and temporally integrated record of grassland isotope composition, useful for ecosystem and environment reconstruction. The effect of altitude on hair 15N is important for studies of trophic relationships: an altitude shift of 2000 m produced the same effect in hair 15N as would a shift from an animal tissue‐based to a plant‐based diet. The similarity of altitude effects on δ13C of individual plant species, vegetation and hair indicates that the effect of altitude on species‐level ‘intrinsic water use efficiency’ scales up linearly to the community and landscape level.

Hair of grazing cattle provides an integrated measure of the effects of site conditions and interannual weather variability on δ13C of temperate humid grassland

AbstractThe carbon isotope composition (δ13C) of C3 ecosystems is sensitive to water availability, and provides important information for the assessment of terrestrial carbon (C) sink/source activity. Here, we report the effects of plant available soil water (PAW) on community 13C signatures of temperate humid grassland. The 5‐year study was conducted on pastures exhibiting a large range of PAW capacity that were located on two site types: peat and mineral soils. The data set included the centennial drought year 2003, and data from wet years (2000 and 2002). Seasonal variation of PAW was modeled using PAW capacity of each pasture, precipitation inputs and evapotranspiration estimates. Community 13C signatures were derived from the δ13C of vegetation and segments of tail switch hair of cattle grown while grazing pastures. Hair 13C signatures provided an assimilation‐weighted 13C signal that integrated both spatial (paddock‐scale) and temporal (grazing season) variation of 13C signatures on a pasture. The δ13C of hair and vegetation increased with decreasing modeled PAW in the same way on mineral and peat soils. But, at a given PAW, the δ13C of hair was 2.6‰ less negative than that of vegetation, reflecting the diet‐hair isotopic shift. Furthermore, the δ13C of hair and vegetation on peat soil pastures was 0.5‰ more negative than on pastures situated on mineral soil. This may have resulted from a ∼10 ppm CO2 enrichment of canopy air derived from ongoing peat mineralization. Community‐scale season‐mean 13C discrimination (Δ) exhibited a saturation‐type response towards season‐mean modeled PAW (r2=0.78), and ranged between 19.8‰ on soils with low PAW capacity during the drought year of 2003, and 21.4‰ on soils with high PAW capacity in a wet year. This indicated relatively small variation in season‐mean assimilation‐weighted pi/pa (0.68–0.75) between contrasting sites and years. However, this range is similar to that reported in other studies, which encompass the range from subtropical arid to humid temperate grassland. Furthermore, the tight relationship between season‐mean Δ and modeled mean PAW suggests that PAW may be used as proxy for Δ.

Spatial and temporal variations in the 13C / 12C and 15N / 14N ratios of mammoth hairs: Palaeodiet and palaeoclimatic implications

Four sets of C and N stable isotope analyses carried out on mammoth hairs of different radiocarbon age from four different sites in northern Siberia are reported here. Another set of analyses from the same region, published elsewhere, is reported for comparison. The analyses were performed on small increments along the length of the hairs providing information about short-(seasonal) and long-term (before and after the Last Glacial maximum) diet variation and, hence, about the environment in which the mammoths lived. The mean δ13C and δ15N values for the four sites range between −24.1‰ and −20.9‰ and between 5.8‰ and 9.6‰, respectively. Both the δ13C and δ15N signals increment towards east when samples from the same age are considered. Hair δ15N correlates well with the current amount of precipitation independently of the radiocarbon age of the sample. This could mean that during the periods considered this environmental parameter did not change significantly in the studied sites. Hair δ13C appears to be affected by a different environmental factor that, in this case, varies in function of the radiocarbon age of the samples. This factor could be the CO2 atmospheric content that, as is well know, varies across a glacial cycle depending on temperature. The isotope patterns obtained from each set of samples exhibit roughly sinusoidal oscillations of the δ13C and δ15N values. These oscillations have been attributed to seasonal changes in the isotope values of the mammoth's diet due to plant adaptation to the different seasonal environmental conditions or to the different seasonal plant type availability. A direct physiological effect on the hair δ15N values can also be considered. This study strongly supports the possibility of using hair δ13C and δ15N signals as indicators of geographical and temporal variation in plant isotope composition and, ultimately, as indicators of palaeoclimate changes.

Carbon isotope analysis of bulk keratin and single amino acids from British and North American hair

The reconstruction of ancient diets using isotopic measurements of bone collagen, and other tissues, which survive in archaeological contexts, relies on known isotopic relationships between diet and body tissues. Examination of these relationships often requires the study of modern human and animal subjects. While hair keratin can act as a useful proxy for bone collagen in isotopic studies on living humans, where it is inappropriate to sample tissues such as collagen, it can, in addition, act as a chronological indicator of dietary change. This study investigates hair keratin delta13C values from current residents of the UK and the USA. Residents in the USA showed a clear bulk hair delta13C enrichment of approximately 3 per thousand over UK individuals, attributed to an elevated C4 dietary input from maize fed to livestock in North America. The keratin delta13C of subjects who moved between the UK and USA showed a pronounced change after relocation, taking approximately 4 months to reach isotopic equilibrium. To investigate these differences further, we measured delta13C values of dispensable and indispensable amino acids as a group, and selected individual amino acids. As a group, enrichment of dispensable amino acids compared with indispensable amino acids occurred in samples from both continents, averaging 7.2 per thousand in the UK and 7.9 per thousand in the USA. Dispensable and indispensable amino acids, as well as all individual amino acids measured, were enriched in samples from the USA compared with those from the UK.

INVESTIGATING TROPHIC RELATIONSHIPS OF PINNIPEDS IN ALASKA AND WASHINGTON USING STABLE ISOTOPE RATIOS OF NITROGEN AND CARBON

AbstractWe measured stable‐nitrogen (δ15N) and stable‐carbon (δ13C) isotope ratios in muscle and hair from 7 northern fur seals (Callorhinus ursinus) from the Pribilof Islands, Alaska, and 27 Steller sea lions (Eumetopias jubatus), and 14 harbor seals (Phoca vitulina) from the Gulf of Alaska and coast of Washington State, in order to contrast dietary information derived from isotopic vs. available conventional dietary studies. Stable‐nitrogen‐isotope analysis of muscle revealed that harbor seals were enriched over sea lions (mean δ15N = 18.6‰vs. 17.5‰) which were in turn enriched over northern fur seals (mean δ15N = 16.6‰). Trophic segregation among these species likely results primarily from differential reliance on herring (Clupea harengus), Atka mackerel (Pleurogrammus monopterygius), and large vs. small walleye pollock (Theregra chalcogramma). According to their δ15N values, adult male Steller sea lions showed a higher trophic position than adult females (mean δ15N: 18.0‰vs. 17.2‰), whereas adult female northern fur seals were trophically higher than juvenile male fur seals (mean δ15N: 16.5‰vs. 15.0‰). Each of these observed differences likely resulted from differential reliance on squid or differences in the size range of pollock consumed. Three northern fur seal pups showed higher δ15N enrichment over adults (mean 17.7‰vs. 15.8‰) due to their reliance on their mother's milk. Stable‐carbon isotope measurements of hair revealed a cline toward more negative values with latitude. Segregation in hair δ13C between Steller sea lions and harbor seals off the coast of Washington (mean δ13C: −13.6‰vs.−15.0‰) reflected the greater association of harbor seals with freshwater input from the Columbia River. Our study demonstrates the utility of the stable isotope approach to augment conventional dietary analyses of pinnipeds and other marine mammals.