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1. 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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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. Isotopic niche partitioning in two sympatric howler monkey species

   https://doi.org/10.1002/ajpa.24028  

   Flores‐Escobar, Elizabeth ; Sanpera, Carolina ; Jover, Lluís ; Cortés‐Ortiz, Liliana ; Rangel‐Negrín, Ariadna ; Canales‐Espinosa, Domingo ; Dias, Pedro Américo D. ( February 2020 , American Journal of Physical Anthropology)

   Ecological similarity between species can lead to interspecific trophic competition. However, when ecologically similar species coexist, they may differ in foraging strategies and habitat use, which can lead to niche partitioning. As the body tissues of consumers contain a stable isotope signature that reflects the isotopic composition of their diet, stable isotope analysis is a useful tool to study feeding behavior. We measured the isotopic niche width, which is a proxy for trophic niche width, of mantled (Alouatta palliata) and black (A. pigra) howler monkeys. Specifically, studied populations in allopatry and sympatry to assess whether these species showed niche partitioning.

   Between 2008 and 2012, we collected hair samples from 200 subjects (113 black and 87 mantled howler monkeys) and used continuous flow isotope ratio mass spectrometry to estimateδ¹³C andδ¹⁵N. We described the isotopic niche width of each species in allopatry and sympatry with the Bayesian estimation of the standard ellipse areas.

   In allopatry, isotopic niche width and isotopic variation were similar in both species. In sympatry, black howler monkeys had a significantly broader isotopic niche, which was mainly determined by highδ¹⁵N values, and included the majority of mantled howler monkeys' isotopic niche. The isotopic niche of mantled howler monkeys did not differ between sympatry and allopatry.

   The coexistence of these ecologically similar species may be linked to trophic niche adjustments by one species, although the particular features of such adjustments (e.g., dietary, spatial, or sensory partitioning) remain to be addressed.

    

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4. 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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5. Sources of variation in maternal allocation in a long‐lived mammal

   https://doi.org/10.1111/1365-2656.13243  

   Macdonald, Kaitlin R. ; Rotella, Jay J. ; Garrott, Robert A. ; Link, William A. ( October 2020 , Journal of Animal Ecology)

   1. Life history theory predicts allocation of energy to reproduction varies with maternal age, but additional maternal features may be important to the allocation of energy to reproduction. 2. We aimed to characterize age-specific variation in maternal allocation and assess the relationship between maternal allocation and other static and dynamic maternal features. 3. Mass measurements of 531 mothers and pups were used with Bayesian hierarchical models to explain the relationship between diverse maternal attributes and both the proportion of mass allocated by Weddell seal mothers, and the efficiency of mass transfer from mother to pup during lactation as well as the weaning mass of pups. 4. Our results demonstrated that maternal mass was strongly and positively associated with the relative reserves allocated by a mother and a pup's weaning mass but that the efficiency of mass transfer declines with maternal parturition mass. Birthdate was positively associated with proportion mass allocation and pup weaning mass, but mass transfer efficiency was predicted to be highest at the mean birthdate. The relative allocation of maternal reserves declined with maternal age but the efficiency of mass transfer to pups increases, suggestive of selective disappearance of poor-quality mothers. 5. These findings highlight the importance of considering multiple maternal features when assessing variation in maternal allocation. 

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