Hair Isotope Research Articles

Investigating infant feeding development in wild chimpanzees using stable isotopes of naturally shed hair.

Measuring the relative contributions of milk and non-milk foods in the diets of primate infants is difficult from observations. Stable carbon (δ13 C) and nitrogen (δ15 N) isotopes in hair can be used to physiologically track infant feeding through development, but few wild studies have done so, likely due to the difficulty in collecting hair non-invasively. We assessed infant feeding at different ages in wild chimpanzees (Pan troglodytes) at Ngogo, Uganda using δ13 C and δ15 N of keratin in 164 naturally shed hairs from 29 infants (61 hairs), 6 juveniles (7 hairs), 28 mothers (67 hairs) and 14 adult males (29 hairs). Hairs were collected when they stuck to feces during defecation or from the ground after chimpanzees groomed or rested. We could not distinguish between the hairs of infants and mothers using strand length and diameter. Infants 1-2 years old were most enriched in 13 C and 15 N and showed means of 1.1‰ in δ13 C and 2.1‰ in δ15 N above their mothers. Infants at 2 years had hair δ13 C values like those of their mothers, which suggests infants began relying more heavily on plants around this age. While mother-infant δ13 C and δ15 N differences generally decreased with offspring age, as is expected when infants rely increasingly more on independent foraging through development, milk seemed to remain an important dietary component for infants older than 2.5 years, as evidenced by continuing elevated δ15 N. We showed that stable carbon and nitrogen isotopes in naturally shed hairs can feasibly detect trophic level differences between chimpanzee infants and mothers. Since it can mitigate some of the limitations associated with behavioral and fecal stable isotope data, the use of hair stable isotopes is a useful, non-invasive tool for assessing infant feeding development in wild primates.

Plasticity in resource use explains the persistence of the largest living rodent in anthropized environments

AbstractHow organisms search for and obtain food is a determinant of their survival. It has been hypothesized that organisms facing food limitations might expand their dietary niche compared with optimal foraging conditions. Nonetheless, some organisms may reduce their dietary niche due to limiting resources. Here, we show the resource use plasticity of capybaras (Hydrochoerus hydrochaeris), the largest living rodent, in natural and anthropized environments of Brazil using stable carbon and nitrogen isotopes in hair. We assessed the resource use, size and overlap of isotopic niches, and the influence of body mass, age class, sex, and landscape composition on isotopic values among 13 capybara populations (210 individuals). We observed a wide variation in isotopic values of capybaras among and within populations in different environments. Surprisingly, diets varied from strictly C4‐based to strictly C3‐based, with most individuals feeding on C4 plants (65%). A substantial portion of individuals presented mixed diets (C3 and C4 plants), totaling 31% of the individuals, and few fed exclusively on C3 plants (4%). Isotopic niche size also varied among populations in both environments, with low overlap considering their core dietary niche. Capybara populations in natural environments had substantial incorporation of C3 resources, showing individuals with strictly C3 diets, and possibly relying on a high diversity of food items, while some populations in anthropized ones fed exclusively on C4 resources. Neither body mass, age class, sex, nor landscape composition significantly influenced isotopic values. Here, we provide evidence of the dietary plasticity of capybaras in different environments, transitioning from the consumption of C4 to C3 plants when needed, that is, from preferred to non‐preferred food items. Together with the species' behavioral plasticity, our results help explain its resilience in surviving, and even thriving, in both natural and human‐modified environments.

Resource Availability, Sex, and Individual Differences in Exploration Drive Individual Diet Specialization.

AbstractIndividual diet specialization (IDS) is widespread and can affect the ecological and evolutionary dynamics of populations in significant ways. Extrinsic factors (e.g., food abundance) and individual variation in energetic needs, morphology, or physiology have been suggested as drivers of IDS. Behavioral traits like exploration and boldness can also impact foraging decisions, although their effects on IDS have not yet been investigated. Specifically, variation among individuals in exploratory behavior and their position along the exploration/exploitation trade-off may affect their foraging behavior, acquisition of food items, and home range size, which may in turn influence the diversity of their diet. Here, we analyzed stable carbon and nitrogen isotopes in hair of wild eastern chipmunks, Tamias striatus, to investigate the influence of individual differences in exploration on IDS. We found that exploration profile, sex, and yearly fluctuations in food availability explained differences in the degree of dietary specialization and in plasticity in stable carbon and stable nitrogen over time. Thus, consistent individual differences in exploration can be an important driver of within-population niche specialization and could therefore affect within-species competition. Our results highlight the need for a more thorough investigation of the mechanisms underlying the link between individual behavioral differences and diet specialization in wild animal populations.

Carbon and nitrogen stable isotope ratios of diet of the Japanese and diet–hair offset values

ABSTRACT The stable isotope ratios of carbon and nitrogen (δ 13C and δ 15N) were measured in composite samples of Japanese food and hair. Three hundred eighty-nine foodstuffs were collected in Tokyo and Gunma Prefecture, Japan, in 2020. The foodstuffs were classified into 15 food categories, prepared as usually consumed, and mixed to make 15 composite samples representing each of the food categories. Similarly prepared samples for foodstuffs collected in 2011 and 2015 were also examined. Composite hair samples were collected from a barber shop in Tokyo and a beauty salon in Gunma in 2019. The δ 13C and δ 15N values of the food and hair composites were measured by elemental analyzer/isotope ratio mass spectrometry after defatting. The δ 13C and δ 15N values of the food composite varied from composite to composite and according to year of collection. The whole-diet δ 13C values were −21.1, −22.0, and −21.5 ‰ for the 2011, 2015, and 2020 samples, respectively; the δ 15N values were 5.0, 4.4, and 4.4 ‰, respectively. Diet–hair offset values of δ 13C and δ 15N were calculated to be 1.9 and 4.3 ‰ for δ 13C and δ 15N, respectively. These offset values will be important for dietary analysis and nutritional research using hair isotope ratios.

Assessing the Reliability of Mobility Interpretation From a Multi-Isotope Hair Profile on a Traveling Individual

Forensic practitioners, archeologists, and ecologists increasingly use hair isotope profiles and isotope databases and maps to reconstruct the life history of unidentified individuals. Relationships between hair isotope profiles with travel history have been primarily investigated through controlled laboratory experiments. However, those controlled studies do not reflect the complex life history of modern individuals who often travel between multiple locations over different periods. Here, we collect one bundle of hairs from a volunteer whose primary residence is in Ottawa (Canada) but who traveled to multiple destinations over a period of 18 months. Those travels include multi-week trips to distant locations and multi-day trips to more local areas. We use multi-isotope profiles on the individual’s hairs coupled with isotope databases across the world to reconstruct travel history at sub-monthly temporal resolution. We compare the isotopic interpretation of mobility with the recorded travel history. A prominent shift in δ2H values is interpreted as a westward movement towards central Canada, which corresponds to a month-long road-trip to the Prairie. We observed a marked negative excursion in δ13C values along the hairs profile, which was related to a multi-week-long trip to several countries in Europe. Except for an exceptionally variable interval likely driven by health issues, δ15N values show very little fluctuation across the entire profile, indicating consumption of consistent amounts of animal or marine-based protein at different locations. The isotopic shifts in the proximal part of the hair reveal a clearer picture of traveling destinations than the shifts in the distal part, which have larger uncertainty in terms of timing and amplitude. Except for the last couple of months before collection, 87Sr/86Sr ratios show little variation throughout the profile likely due to recent exchange with Ottawa tap water during bathing or showering. The different 87Sr/86Sr ratios in the month preceding collection appear to partially preserve the 87Sr/86Sr ratio of the volunteer’s diet. This study demonstrates the interest of using multi-isotope systems and large isotopic databases to reconstruct individual mobility. This study also underlines the challenges in linking isotope data to mobility, particularly in rapidly growing keratinous tissues.

Assessing geographic controls of hair isotopic variability in human populations: A case-study in Canada.

Studying the isotope variability in fast-growing human tissues (e.g., hair, nails) is a powerful tool to investigate human nutrition. However, interpreting the controls of this isotopic variability at the population scale is often challenging as multiple factors can superimpose on the isotopic signals of a current population. Here, we analyse carbon, nitrogen, and sulphur isotopes in hair from 590 Canadian resident volunteers along with demographics, dietary and geographic information about each participant. We use a series of machine-learning regressions to demonstrate that the isotopic values in Canadian residents' hair are not only influenced by dietary choices but by geographic controls. First, we show that isotopic values in Canadian residents' hair have a limited range of variability consistent with the homogenization of Canadian dietary habits (as in other industrialized countries). As expected, some of the isotopic variability within the population correlates with recorded individual dietary choices. More interestingly, some regional spatial patterns emerge from carbon and sulphur isotope variations. The high carbon isotope composition of the hair of eastern Canadians relative to that of western Canadians correlates with the dominance of corn in the eastern Canadian food-industry. The gradient of sulphur isotope composition in Canadian hair from coast to inland regions correlates with the increasing soil pH and decreasing deposition of marine-derived sulphate aerosols in local food systems. We conclude that part of the isotopic variability found in the hair of Canadian residents reflects the isotopic signature associated with specific environmental conditions and agricultural practices of regional food systems transmitted to humans through the high consumption rate of intra-provincial food in Canada. Our study also underscores the strong potential of sulphur isotopes as tracers of human and food provenance.

Stable isotopes in hair reveal dietary protein sources with links to socioeconomic status and health

Carbon and nitrogen isotope ratios in hair sampled from 65 communities across the central and intermountain regions of the United States and more intensively throughout 29 ZIP codes in the Salt Lake Valley, Utah, revealed a dietary divergence related to socioeconomic status as measured by cost of living, household income, and adjusted gross income. Corn-fed, animal-derived proteins were more common in the diets of lower socioeconomic status populations than were plant-derived proteins, with individual estimates of animal-derived protein diets as high as 75%; United States towns and cities averaged 57%. Similar patterns were seen across the socioeconomic status spectrum in the Salt Lake Valley. It is likely that corn-fed animal proteins were associated with concentrated animal-feeding operations, a common practice for industrial animal production in the United States today. Given recent studies highlighting the negative impacts of animal-derived proteins in our diets, hair carbon isotope ratios could provide an approach for scaling assessments of animal-sourced foods and health risks in communities across the United States.

How isotopic signatures relate to meat consumption in wild chimpanzees: A critical reference study from Taï National Park, Côte d’Ivoire

The roots of human hunting and meat eating lie deep in our evolutionary past shared with chimpanzees (Pan troglodytes). From the few habituated wild populations, we know that there is considerable variation in the extent to which chimpanzees consume meat. Expanding our knowledge of meat eating frequencies to more, yet unhabituated, populations requires noninvasive, indirect quantitative techniques. We here evaluate the use of stable isotopes to reconstruct meat-eating behavior in wild chimpanzees. We present hair isotope data (n = 260) of two western chimpanzee (P. troglodytes verus) groups from Taï forest (Côte d’Ivoire) and relate them to directly observed amounts of meat consumed, sex/female reproductive state, and group, while controlling for differences between individuals, seasons, and observation efforts. Succeeding seven months of hunting observations, we collected hair of 25 individuals for sequential analysis of δ15N and δ13C. Hunting success in the 7-month study period varied between the groups, with 25 successful hunts in the East group and only 8 in the North group. However, our models only found a direct relationship between amounts of meat consumed and variation within individual hair δ15N values in the East group, but not in the North group and not when comparing between individuals or groups. Although on average East group individuals consumed more than double the amount of meat than North group individuals, their δ15N values were significantly lower, suggesting that differences in microhabitat are substantial between group territories. The effect of sex/female reproductive state was significant in δ15N and δ13C, suggesting it related to access to food or feeding preferences. We conclude that several factors additional to diet are influencing and thus obscuring the isotope ratios in wild chimpanzee hair, particularly when comparing between sexes and social groups.

Spatial variations in oxygen and hydrogen isotopes in waters and human hair across South Korea

The spatial distribution of isotopic signatures in the form of isoscape is a valuable tool to map their spatial heterogeneity in various environmental settings. However, only limited information about δ18O and δ2H in water across South Korea is available and to our knowledge no study so far has tried to examine the isotopic heterogeneity of tap water and human scalp hair in South Korea. Here, we present the first national scale analyses of stream water, groundwater, tap water, and human scalp hair isoscapes for South Korea. Stream water, groundwater, tap water, and human scalp hair samples were collected from across South Korea. These samples were analyzed for δ18O and δ2H, and the isotopic data were then used to generate interpolated δ18O and δ2H isoscapes for South Korea. The results of linear regression analyses showed strong and significant relationships between δ18Ohair and δ18Owater (R2 = 0.83, P < 0.002) and between δ2Hhair and δ2Hwater (R2 = 0.74, P < 0.006), primarily reflecting a close co-relationship between water and hair. The slopes of linear regressions for δ18O (Δδ18Ohair/Δδ18Owater) and δ2H (Δδ2Hhair/Δδ2Hwater) suggested that approximately 27% of hydrogen and 36% of oxygen in hair keratin were derived from the local drinking water. Interpolated δ18O and δ2H isotope maps of stream water, groundwater, and tap water samples collected from across South Korea showed similar spatial patterns of isotope variability. These samples showed a clear latitudinal gradient with high isotopic values in the south which progressively decrease toward the north. The same trends were observed in hair isoscapes as well, and had gradients matching the isotopic pattern of water samples. The strong relationship between water and human hair, and the consistent spatial pattern between them suggest that hair isotope signatures in South Korea can be used in provenance- and forensic-related activities.

Oxygen and Hydrogen Isotopes in Human Hair and Tap Water: Modeling Relationships in a Modern Mexican Population

This study investigated the relationship between 18O and 2H isotopes in samples of Mexican hair and drinking water. The purpose of this study was twofold: to quantify the relationship between isotopes in Mexican hair and tap water, in order to understand the impact of water stress and differing socioeconomic status on accurate predictions of drinking water; and to determine whether currently existing semimechanistic models can accurately represent the relationship between hair and tap water. This study used a subset of paired samples of human hair (n = 62) and tap water (n = 76). Isotope values in tap water ranged from –11.4‰ to –4.3‰ and –79.1‰ to –22.5‰, and in hair from +9.5‰ to +16.1‰ and –90.8‰ to –53.7‰, for δ18O and δ2H, respectively. The most depleted δ18O and δ2H hair values came from individuals in the state of Morelos. For modern Mexican populations, positive correlations between isotopes in hair and water were not significant, with correlation coefficients r = 0.61 (p = 0.05) and r = 0.60 (p = 0.06) for 18O and 2H, respectively. Error-in-variables regression yielded linear fits that were somewhat better for 2H relative to 18O: δ18Oh = 0.183 [±0.132] δ18Otw + 15.7 [±0.9]‰ (r2 = 0.23); δ2Hh = 0.181 [±0.076] δ2Htw – 64.0 [±3.0]‰ (r2 = 0.34). In short, data from this Mexican population did not exhibit the strong relationships between isotope values of 18O and 2H in tap water and hair that have been characteristic of other populations studied to date. Given the economic stratification of this region and the poor correlation between hair and water samples, the authors considered the possibility that l, the fraction of the diet derived from local sources, and fs, the fraction of nonexchangeable H in keratin that was fixed in vivo, are local rather than global parameters for this population. The authors estimated different values of l and fs for each location. Given the anticipated importance of the nonlocal dietary contribution, they treated the isotopic content of nonlocal food and the offset parameters for predicting isotopes in locally derived food as tuning parameters and compared the results with parameters based on the American supermarket diet. They found that, although O and H isotopes in water and hair maintained similar geographic distributions, O and H isotopes in tap water explained only a small part of the variation observed in hair samples. Compared to the standard American supermarket diet, the Mexican estimates for nonlocal diet and local diet offsets predicted regional distributions of l and fs that cleanly segregated urban areas from rural towns.

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.

Stable isotope ratio analysis (C, N, S) of hair from modern humans in Ethiopia shows clear differences related to subsistence regimes

We measured the stable isotope ratios (C, N, S) of modern human hair collected from 49 people in rural southern Ethiopia to characterize and compare the stable isotope signatures of interacting and ethnically distinct populations with differing economic practices (farmers, pastoralists, fishers) in order to determine if the dietary differences are visible and measurable in their hair isotope values. We found that there were significant differences in all three elements that can distinguish these economic practices (carbon: Χ2 = 8.523, p = 0.014; nitrogen: Χ2 = 35.372, p < 0.001; and sulfur: Χ2 = 30.887, p < 0.001). These results demonstrate the utility of isotopic methods as an indicator of dietary difference in living populations and shows that diverse dietary adaptations and economies even among interacting and neighboring peoples can be distinguished in this region of Ethiopia.

Parasites in Myodes glareolus and their association with diet assessed by stable isotope analysis.

Vertebrates are hosts to numerous parasites, belonging to many different taxa. These parasites differ in transmission, being through either direct contact, a faecal-oral route, ingestion of particular food items, vertical or sexual transmission, or by a vector. Assessing the impact of diet on parasitism can be difficult because analysis of faecal and stomach content are uncertain and labourious; and as with molecular methods, do not provide diet information over a longer period of time. We here explored whether the analysis of stable isotopes in hair provides insight into the impact of diet and the presence of parasites in the rodent Myodes glareolus. Twenty-one animals were examined for parasites and their hair analysed for stable isotopes (C and N). A positive correlation between δ15N and one species of intestinal parasite was observed in females. Furthermore, several ectoparasites were negatively correlated with δ15N, indicating that infections are further associated with foraging habits (size and layout of the home range, length and timing of foraging, interaction with other rodents, etc.) that set the rodents in direct contact with infected hosts. Although a limited number of animals were included, it seemed that the isotope values allowed for identification of the association between diet and parasite occurrence in this rodent. We therefore propose that this method is useful in providing further insight into host biology, feeding preferences and potential exposure to parasites species, contributing to the understanding of the complex relationship between hosts and parasites.

Evaluation of childhood nutrition by dietary survey and stable isotope analyses of hair and breath.

The natural abundances of carbon, nitrogen, and sulfur stable isotopes in hair, and of carbon isotopes in breath serve as quantitative biomarkers of protein and carbohydrate sources, but applicability of isotopes for evaluating children's diet has not been demonstrated. In this study, we sought to describe the stable isotope patterns observed in the hair and breath of children and to assess dietary variations in relation to age and ethnicity, hypothesizing that these would reflect dietary differences across age and ethnic groups and would correlate with intake variables derived from a Food Frequency Questionnaire. Data were obtained from a cross-sectional study of non-Hispanic white (N = 115) and Hispanic (N = 97) children, aged 9-16 years, in Salt Lake City, Utah. Sampling included a hair sample, breath samples (AM and PM), and a youth/adolescent food questionnaire (YAQ). Hair was analyzed for carbon (δ13 C), nitrogen (δ15 N), and sulfur (δ34 S) isotopes, and breath samples for δ13 CAM/PM of respired CO2 . Non-Hispanic whites had lower δ13 C, δ15 N, δ13 CAM , and δ13 CPM values than Hispanics. Hair δ13 C and δ15 N values were correlated with protein sources, particularly for non-Hispanics. Breath δ13 C values were correlated with carbohydrate sources, particularly for Hispanic students. Non-Hispanic white students reported greater intake of total protein, animal protein, dairy, and grain than Hispanic students. Hispanic students reported higher intake of carbohydrates, particularly sweetened beverages. While YAQ and stable isotope data reflected strong cultural influences in diet, no significant gender-based nor age-based differences were detected. Significant covariation between YAQ and isotopes existed and demonstrate the potential of stable isotopes for characterizing children's diet.

Dietary seasonal variations in the Medieval Nubian population of Kulubnarti as indicated by the stable isotope composition of hair

ObjectivesThe island of Kulubnarti is located in Sudanese Nubia and contains two cemeteries, named R and S, which are dated to AD 550–800. In order to provide more detailed dietary information for this population and examine seasonality of diet, we analyzed the carbon isotope composition of hair samples from both cemeteries. Materials and methodsForty seven separate hair samples from 8 adults, 29 adolescents, 7 infants and 3 individuals with unknown age were analyzed. Long hair samples were cut transversely and divided into 2 cm longitudinal segments, to examine temporal variations in the dietary carbon sources. ResultsThe average carbon isotope value for the whole population was −17.95‰ (SD = 1.8). A significant difference between the two cemeteries was found with variances in the amount of C4 dietary carbon sources consumed. DiscussionThe results of hair isotope compositions concur with previous soft tissue investigations of Kulubnarti population which suggested that the dietary regimen contains a mix of C3 and C4 plant-based sources. A seasonal variation in diet can be inferred from the sequential hair segments of Kulubnarti individuals. These suggest a dietary transition between dominant C3 plant-based sources in winter to dominant C4 ones in summer with a small contribution of the non-harvested, alternative, crop.

Oxygen and Hydrogen Isotopes in Human Hair and Tap Water: Modeling Relationships in a Modern Mexican Population

This study investigated the relationship between 18O and 2H isotopes in samples of Mexican hair and drinking water. The purpose of this study was twofold: to quantify the relationship between isotopes in Mexican hair and tap water, in order to understand the impact of water stress and differing socioeconomic status on accurate predictions of drinking water; and to determine whether currently existing semimechanistic models can accurately represent the relationship between hair and tap water. This study used a subset of paired samples of human hair (n = 62) and tap water (n = 76). Isotope values in tap water ranged from -11.4‰ to -4.3‰ and -79.1‰ to -22.5‰, and in hair from +9.5‰ to +16.1‰ and -90.8‰ to -53.7‰, for δ18O and δ2H, respectively. The most depleted δ18O and δ2H hair values came from individuals in the state of Morelos. For modern Mexican populations, positive correlations between isotopes in hair and water were not significant, with correlation coefficients r = 0.61 (p = 0.05) and r = 0.60 (p = 0.06) for 18O and 2H, respectively. Error-in-variables regression yielded linear fits that were somewhat better for 2H relative to 18O: δ18Oh = 0.183 [±0.132] δ18Otw + 15.7 [±0.9]‰ (r2 = 0.23); δ2Hh = 0.181 [±0.076] δ2Htw - 64.0 [±3.0]‰ (r2 = 0.34). In short, data from this Mexican population did not exhibit the strong relationships between isotope values of 18O and 2H in tap water and hair that have been characteristic of other populations studied to date. Given the economic stratification of this region and the poor correlation between hair and water samples, the authors considered the possibility that l, the fraction of the diet derived from local sources, and fs, the fraction of nonexchangeable H in keratin that was fixed in vivo, are local rather than global parameters for this population. The authors estimated different values of l and fs for each location. Given the anticipated importance of the nonlocal dietary contribution, they treated the isotopic content of nonlocal food and the offset parameters for predicting isotopes in locally derived food as tuning parameters and compared the results with parameters based on the American supermarket diet. They found that, although O and H isotopes in water and hair maintained similar geographic distributions, O and H isotopes in tap water explained only a small part of the variation observed in hair samples. Compared to the standard American supermarket diet, the Mexican estimates for nonlocal diet and local diet offsets predicted regional distributions of l and fs that cleanly segregated urban areas from rural towns.

Poe in Richmond: Poe's Tell-Tale Hair at the Poe Museum

Poe in Richmond: Poe's Tell-Tale Hair at the Poe Museum

Compatibility of preparatory procedures for the analysis of cortisol concentrations and stable isotope (δ13C, δ15N) ratios: a test on brown bear hair.

The measurement of naturally occurring glucocorticoids and stable isotopes of several elements has gained importance in wildlife studies in recent decades and opened a myriad of ecological applications. Cortisol and stable isotopes equilibrate in animal tissues over periods of integration related to the growth rate of the tissue, providing information reflecting systemic cortisol secretion and dietary intake. Sample preparation shares the common step of first cleaning the sample of external contamination. However, it is not well understood how different solvents used in sample preparation affect isotopic and cortisol values, and whether it is safe to follow the same procedures for both measures to optimize analyses of the same sample. We conducted an experiment to compare different preparation protocols for the analysis of cortisol concentrations and stable carbon (δ13C) and nitrogen (δ15N) isotope ratios in hair. Hair samples from 12 brown bears (Ursus arctos) were each divided into five aliquots; two aliquots were rinsed with a 2:1 chloroform:methanol (v/v) mixture with one aliquot ground prior to cortisol analysis and the other left intact for stable isotope analyses; two aliquots were washed with methanol with one aliquot ground prior to cortisol analysis and the other left intact for stable isotope analyses; and one aliquot washed with methanol and ground prior to stable isotope analyses. The cortisol, δ13C and δ15N values remained consistent following all treatments. Our results indicate that hair samples rinsed with a 2:1 chloroform:methanol mixture or washed with methanol can be used for both types of analyses. Further, hair that has been ground in a standard hair cortisol procedure can also be used for stable isotope analysis. This information is important for improving laboratory efficiency and compatibility of procedures used for wildlife physiological ecology studies where concurrent measurements of cortisol and stable isotopes in hair are required.

Isotopic composition of sheep wool records seasonality of climate and diet.

Hair keratin is a very important material in ecological and archaeological studies because it grows continuously, can be obtained non-invasively, does not require extensive processing prior to analysis and can be found in archaeological sites. Only a few studies have examined seasonal variations in hair isotope values, and there is no published dataset examining the isotope variability recorded in the keratinous tissues of stationary (i.e., non-migrating) domestic mammals. Thirty-six Irish sheep were sampled in eight farms every three months between September 2006 and June 2007. A shearing strategy was adopted to sample only the most recently grown wool in order to represent an average of the summer, autumn, winter and spring conditions. The stable isotope ratios of the ground samples were measured using two different stable isotope mass spectrometers operated in dual-inlet (C, N) and continuous-flow (O, H) mode. Wool O isotope ratios are a good proxy for seasonal variability in climate and can be used to anchor a chronology independently of other isotope records (C, N) that are influenced by diet or physiology. By contrast, interpretation of seasonal variations in hair H isotope composition in terms of climate is more complex probably due to the influence of dietary H. The C and N isotope values of grass-fed animals varied seasonally, probably reflecting the annual cycle of seasonal variation in grass isotope values. The highest δ(13) C values were measured in summer-grown wool, while the highest δ(15) N values were measured in winter-grown wool. Supplementation of the sheep diet with concentrates was detected easily and was marked by an increase in δ(13) C values and a decrease in δ(15) N values in winter-grown wool. The present study demonstrates that time-resolved sampling and stable isotope ratio analysis of sheep wool can be used to identify short-term changes in diet and climate and therefore offer a tool to examine a wide variety of present and past husbandry practices.

Feeding Habits of Introduced Black Rats, Rattus rattus, in Nesting Colonies of Galapagos Petrel on San Cristóbal Island, Galapagos.

Introduced rodents are responsible for ecosystem changes in islands around the world. In the Galapagos archipelago, their effects on the native flora and fauna are adverse, including the extinction of endemic rodents in some islands and the reduction in the reproductive success of the Galapagos petrel (Pterodroma phaeopygia) in its nesting zones. Understanding the feeding behavior of introduced rodents and their trophic interactions with native and non-native species on islands, can assist in the design of management strategies and conservation plans of invasive and endemic species respectively. Four petrel nesting colonies were monitored during June 2013 on San Cristóbal Island (El Plátano, El Junco, San Joaquín, and La Comuna). The feeding habits of black rats were evaluated by analyzing stomach contents and stable isotopes in hair. Three species of introduced rodents were captured. R. rattus was the most abundant at all sites (n=43, capture success (CS) = 55.8%), followed by the house mouse, Mus musculus (n = 17, CS = 37.8%), and the Norwegian rat, R. norvegicus (n = 4, CS = 4.5%), captured only at La Comuna. The omnivorous black rat ate mostly plants (98%) and arthropods (2%). Intact seeds of Miconia robinsoniana were the main food at all sites (relative abundance=72.1%, present in 95% of the analyzed stomachs), showing the black rats’ possible role in the archipelago as endemic seed dispersers. There was no evidence of petrel’s intake; however, its possible consumption is not discarded at all. The δ15N and δ13C analysis corroborated the primarily herbivorous diet of black rats. The isotopic signatures of the three rodent species reflect the inter- and intra-specific differential use of food resources. Black rat showed a wider diet in La Comuna, which was related to a lower availability of its primary prey and its ability to adapt to the available resources in its habitat.