Compound‐specific stable hydrogen isotope (δ²H) analyses of fatty acids: A new method and perspectives for trophic and movement ecology

Abstract

Rationale: Compound-specific stable isotope analysis (CSIA) is a powerful tool to better understand trophic transfer of dietary molecules in and across ecosystems. Hydrogen isotope values ( 2 H) in consumer tissues have potential to more clearly distinguish dietary sources than 13 C or 15 N within and among habitats but have not been used at the fatty acids level for ecological purposes.Methods: Here we demonstrate a new online high-capacity gas chromatography-isotope ratiomass spectrometry technique ( 2 H-CSIA) that offers accurate and reproducible determinations of δ 2 H values on a range of fatty acids from organisms of aquatic food webs.Results: We show that δ 2 H of lipid extracts obtained from aquatic organisms, such as biofilms, leaves, invertebrates, or fish muscle tissue have distinctive δ 2 H that can be used to assess sources and trophic interactions, as well as dietary allocation and origin of fatty acids within consumer tissue. Conclusions:The new 2 H-CSIA method can be applied to evaluate sources and trophic dynamics of fatty acids in organisms ranging from food web ecology, migratory connectivity.

The majority of brain palmitic acid is maintained by lipogenesis from dietary sugars and is augmented in mice fed low palmitic acid levels from birth

“…In the future, studies could utilize dietary inputs in controlled feeding studies with increased δ 13 C signals, ultimately making it more feasible to identify relatively small isotopic changes endogenously. This could include identifying dietary sources at the natural abundance level with a wider range of enrichment between the most and least enriched source, such as the extension of hydrogen isotopes (δ 13 H) in the CSIA of fatty acids (Pilecky et al, 2021), or, utilizing artificially enriched 13 C molecules to measure isotopic effects on a larger scale. Finally, techniques to confirm local brain DNL from dietary sugars alongside δ 13 C‐PAM, such as whole‐brain FAS‐KO models could further validate the use of carbon isotopes at the natural abundance level to measure DNL from dietary sugars.…”

Hydrogen isotopes (δ2H) of polyunsaturated fatty acids track bioconversion by zooplankton

“…2 H‐ and 13 C‐CSIA were performed according to Pilecky, Winter, et al. (2021), Pilecky, Kämmer, et al. (2021), using a Thermo Trace 1310 GC (ThermoFisher), coupled by a ConFlo IV interface (ThermoFisher) to a continuous‐flow isotope‐ratio mass spectrometer (DELTA V Advantage, ThermoFisher).…”

“…FA δ 13 C/δ 2 H values () were corrected for the methyl group addition during methylation according to Pilecky, Winter, et al. (2021) and Pilecky, Kämmer, et al. (2021).…”

“…2 H-and 13 C-CSIA were performed according to Pilecky, Winter, et al (2021), Pilecky, Kämmer, et al (2021) For δ 2 H analysis of pond and experimental waters used, three replicates each sample were filtered before isotope analysis using a L2130-I (Picarro Inc.) and using the techniques described elsewhere (Coplen & Wassenaar, 2015). For waters with D 2 O added, we used IAEA-604 (+799.0‰) and IAEA VSMOW2 (0.0‰) as our bracketing standards.…”

“…Compound‐specific stable isotope analyses (CSIA) of FA allow natural tracing of FA sources and, compared to bulk stable isotope analysis, are more informative at disentangling food web interactions (Pilecky, Kämmer, et al., 2021; Pilecky, Winter, et al., 2021; Twining et al., 2020). The typically large δ 2 H differences between aquatic versus terrestrial sources (Hobson et al., 2020; Solomon et al., 2009) offer a new and promising approach for 2 H‐CSIA to better understand the sources and fate of FA in food webs.…”