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1. Changes in stable isotope compositions during fasting in phocid seals

   https://doi.org/10.1002/rcm.8308  

   Habran, Sarah ; Damseaux, France ; Pomeroy, Paddy ; Debier, Cathy ; Crocker, Daniel ; Lepoint, Gilles ; Das, Krishna ( December 2018 , Rapid Communications in Mass Spectrometry)

   The grey seal,Halichoerus grypus(GS), and the northern elephant seal,Mirounga angustirostris(NES), come ashore for reproduction. This period involves intense physiological processes such as lactation in females and a developmental post‐weaning fast in juveniles. Previous studies have shown thatδ¹³C andδ¹⁵N values are affected by starvation, but the precise effects of fasting associated with lactation and post‐weaning fast in seals remain poorly understood.

   To examine the effect of lactation and post‐weaning fast on stable isotope ratios in GS and NES, blood and hair were sampled from 21 GS mother‐pup pairs on the Isle of May and on 22 weaned NES pups at Año Nuevo State Reserve during their respective breeding seasons. Milk samples were also collected from GS mothers. Stable isotope measurements were performed with an isotope ratio mass spectrometer coupled to an N‐C elemental analyser.

   Changes in stable isotope ratios in blood components during fasting were similar and weak between GS and NES mothers especially in blood cells (GS:Δ¹⁵N = 0.05‰,Δ¹³C = 0.02‰; NES:Δ¹⁵N = 0.1‰,Δ¹³C = 0.1‰). GS showed a¹⁵N discrimination factor between maternal and pup blood cells and milk, but not for¹³C. The strongest relationship between the isotopic compositions of the mother and the pup was observed in the blood cells.

   Isotopic consequences of lactation, fasting, and growth seem limited in NES and GS, especially in medium‐term integrator tissues of feeding activity such as blood cells. Stable isotope ratios in the blood of pups and mothers are correlated. We observed a subtle mother‐to‐pup fractionation factor. Our results suggest that pup blood cells are mostly relevant for exploring the ecology of female seals.

    

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2. Effects of drying methods on plant lipid compounds and bulk isotopic compositions

   https://doi.org/10.1002/rcm.8900  

   Suh, Yeon Jee ; Diefendorf, Aaron F. ( August 2020 , Rapid Communications in Mass Spectrometry)

   Plant lipid biomarkers, such as plant waxes and terpenoids, and the stable isotopic composition of bulk leaves are widely used in both modern and paleoclimate studies for tracking vegetation and climate. However, the effects of different drying methods on the preservation of plant lipid biomarkers and the stable isotopic compositions of leaves are less explored. Here, we investigated various drying methods for the measurement of plant lipid concentrations and bulk leaf isotopic compositions.

   Leaves from four tree species (Acer rubrum,Pinus sylvestris,Platanus occidentalis, andTaxodium distichum) were collected and dried using air, an oven, a freeze‐dryer, and a microwave. We compared concentrations of leaf waxes and terpenoids and carbon (δ¹³C) and nitrogen (δ¹⁵N) isotopic compositions of leaves by different drying methods.

   The air, oven, freeze‐dryer, and microwave drying methods did not affect lipid concentrations significantly, and only a few homologues differed (38.1% or 41.8 μg/g on average) possibly due to biological variations or enhanced extraction efficiencies. The δ¹³C values were not affected by drying methods, whereas the δ¹⁵N values in oven‐dried leaves in some species were higher by 0.2–0.7‰ than those obtained by other methods. Though small, we attribute these patterns to loss of leaf compounds with lower isotope ratios during oven‐drying.

   Based on our results, each drying technique yielded equivalent results for all plant wax and terpenoid concentrations and bulk leaf δ¹³C values; however, oven‐drying modified the δ¹⁵N values.

    

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3. Effects of chemical preservation on bulk and amino acid isotope ratios of zooplankton, fish, and squid tissues

   https://doi.org/10.1002/rcm.8408  

   Hetherington, Elizabeth D. ; Kurle, Carolyn M. ; Ohman, Mark D. ; Popp, Brian N. ( April 2019 , Rapid Communications in Mass Spectrometry)

   It is imperative to understand how chemical preservation alters tissue isotopic compositions before using historical samples in ecological studies. Specifically, although compound‐specific isotope analysis of amino acids (CSIA‐AA) is becoming a widely used tool, there is little information on how preservation techniques affect amino acidδ¹⁵N values.

   We evaluated the effects of chemical preservatives on bulk tissueδ¹³C andδ¹⁵N and amino acidδ¹⁵N values, measured by gas chromatography/isotope ratio mass spectrometry (GC/IRMS), of (a) tuna (Thunnus albacares) and squid (Dosidicus gigas) muscle tissues that were fixed in formaldehyde and stored in ethanol for 2 years and (b) two copepod species,Calanus pacificusandEucalanus californicus, which were preserved in formaldehyde for 24–25 years.

   Tissues in formaldehyde‐ethanol had higher bulkδ¹⁵N values (+1.4,D. gigas; +1.6‰,T. albacares), higherδ¹³C values forD. gigas(+0.5‰), and lowerδ¹³C values forT. albacares(−0.8‰) than frozen samples. The bulkδ¹⁵N values from copepods were not different those from frozen samples, although theδ¹³C values from both species were lower (−1.0‰ forE. californicusand −2.2‰ forC. pacificus) than those from frozen samples. The mean amino acidδ¹⁵N values from chemically preserved tissues were largely within 1‰ of those of frozen tissues, but the phenylalanineδ¹⁵N values were altered to a larger extent (range: 0.5–4.5‰).

   The effects of preservation on bulkδ¹³C values were variable, where the direction and magnitude of change varied among taxa. The changes in bulkδ¹⁵N values associated with chemical preservation were mostly minimal, suggesting that storage in formaldehyde or ethanol will not affect the interpretation ofδ¹⁵N values used in ecological studies. The preservation effects on amino acidδ¹⁵N values were also mostly minimal, mirroring bulkδ¹⁵N trends, which is promising for future CSIA‐AA studies of archived specimens. However, there were substantial differences in phenylalanine and valineδ¹⁵N values, which we speculate resulted from interference in the chromatographic resolution of unknown compounds rather than alteration of tissue isotopic composition due to chemical preservation.

    

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4. Nitrogen stable isotope turnover and discrimination in lizards

   https://doi.org/10.1002/rcm.9030  

   Warne, Robin W. ; Wolf, Blair O. ( January 2021 , Rapid Communications in Mass Spectrometry)

   Nitrogen stable isotope ratio (δ¹⁵N) processes are not well described in reptiles, which limits reliable inference of trophic and nutrient dynamics. In this study we detailed δ¹⁵N turnover and discrimination (Δ¹⁵N) in diverse tissues of two lizard species, and compared these results with previously published carbon data (δ¹³C) to inform estimates of reptilian foraging ecology and nutrient physiology.

   We quantified¹⁵N incorporation and discrimination dynamics over 360 days in blood fractions, skin, muscle, and liver ofSceloporus undulatusandCrotaphytus collaristhat differed in body mass. Tissue samples were analyzed on a continuous flow isotope ratio mass spectrometer.

   Δ¹⁵N for plasma and red blood cells (RBCs) ranged between +2.7 and +3.5‰; however, skin, muscle, and liver did not equilibrate, hindering estimates for these somatic tissues.¹⁵N turnover in plasma and RBCs ranged from 20.7 ± 4 to 303 ± 166 days among both species. Comparison with previously published δ¹³C results for these same samples showed that¹⁵N and¹³C incorporation patterns were uncoupled, especially during winter when hibernation physiology could have played a role.

   Our results provide estimates of¹⁵N turnover rates and discrimination values that are essential to using and interpreting isotopes in studies of diet reconstruction, nutrient allocation, and trophic characterization in reptiles. These results also suggest that somatic tissues can be unreliable, while life history shifts in nutrient routing and metabolism potentially cause¹⁵N and¹³C dynamics to be decoupled.

    

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5. Assessment of nutritional stress in famine burials using stable isotope analysis

   https://doi.org/10.1002/ajpa.24054  

   Walter, Brittany S. ; DeWitte, Sharon N. ; Dupras, Tosha ; Beaumont, Julia ( April 2020 , American Journal of Physical Anthropology)

   We compared δ¹⁵N and δ¹³C values from bone and dentine collagen profiles of individuals interred in famine‐related and attritional burials to evaluate whether individuals in medieval London who experienced nutritional stress exhibit enriched nitrogen in bone and tooth tissue. Dentine profiles were evaluated to identify patterns that may be indicative of famine during childhood and were compared with the age of enamel hypoplasia (EH) formation to assess whether isotopic patterns of undernutrition coincide with the timing of physiological stress.

   δ¹⁵N and δ¹³C isotope ratios of bone collagen were obtained from individuals (n= 128) interred in attritional and famine burials from a medieval London cemetery (c. 1120–1539). Temporal sequences of δ¹⁵N and δ¹³C isotope profiles for incrementally forming dentine collagen were obtained from a subset of these individuals (n= 21).

   Results indicate that individuals from attritional graves exhibit significantly higher δ¹⁵N values but no significant differences were found between burial types for the sexes. Analyses of dentine profiles reveal that a lower proportion of famine burials exhibit stable dentine profiles and that several exhibit a pattern of opposing covariance between δ¹⁵N and δ¹³C. EH were also observed to have formed during or after the opposing covariance pattern for some individuals.

   The results of this study may reflect differences in diet between burial types rather than nutritional stress. Though nutritional stress could not be definitively identified using bone and dentine collagen, the results from dentine analysis support previous observations of biochemical patterns associated with nutritional stress during childhood.

    

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