Use of compound‐specific nitrogen isotope analysis of amino acids in trophic ecology: assumptions, applications, and implications

Ishikawa, Naoto F.

doi:10.1007/s11284-018-1616-y

Cited by 48 publications

(44 citation statements)

References 91 publications

(135 reference statements)

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“…However, TDF Glu‐Phe in arachnid predators was significantly lower on all diets, presumably due to higher diet quality, guanine excretion, and fluid‐feeding, suggesting that it has to be adapted to a lower value and supporting the call for multi‐TDF approaches (Germain et al. , McMahon and McCarthy , Ishikawa ). While eAAs in springtails were not significantly fractionated in 13 C from diet to consumer, there was a negative fractionation in arachnids.…”

Section: Discussionmentioning

confidence: 79%

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Compound‐specific isotope analysis of amino acids as a new tool to uncover trophic chains in soil food webs

Pollierer

Larsen

Potapov

et al. 2019

Ecological Monographs

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Food webs in soil differ fundamentally from those aboveground; they are based on inputs from both living plants via root exudates, and from detritus, which is a complex mixture of fungi, bacteria, and dead plant remains. Trophic relationships are difficult to disentangle due to the cryptic lifestyle of soil animals and inevitable microbial contributions to their diet. Compound‐specific isotope analysis of amino acids (AAs) is increasingly used to explore complex food webs. The combined use of AA δ13C and δ15N values is a promising new approach to disentangle trophic relationships since it provides independent but complementary information on basal resources, as well as the trophic position of consumers. We conducted a controlled feeding study in which we reconstructed trophic chains from main basal resources (bacteria, fungi, plants) to primary consumers (springtails, oribatid mites) and predators (gamasid mites, spiders). We analyzed dual compound‐specific isotope AA values of both resources and consumers. By applying an approach termed “stable isotope (13C) fingerprinting” we identified basal resources, and concomitantly calculated trophic positions using 15N values of trophic and source AAs in consumers. In the 13C fingerprinting analysis, consumers in general grouped close to their basal resources. However, higher than usual offsets in AA δ13C between diet and consumers suggest either gut microbial supplementation or the utilization of specific resource fractions. Identification of trophic position crucially depends on correct estimates of the trophic discrimination factor (TDFGlu‐Phe), which was close to the commonly applied value of 7.6‰ in primary consumers feeding on microbial resources, but considerably lower in arachnid predators (~2.4‰), presumably due to higher diet quality, excretion of guanine, and fluid feeding. While our feeding study demonstrates that dual compound‐specific AA analyses hold great promise in delineating trophic linkages among soil‐dwelling consumers and their resources, it also highlights that a “one‐size‐fits‐all” approach to TDFGlu‐Phe does not apply to soil food webs.

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Section: Discussionmentioning

confidence: 79%

“…, McMahon and McCarthy , Blanke et al. , Ishikawa ). In the present study, TDF Glu‐Phe varied significantly between primary consumers and predators, with the variation depending on basal resources.…”

Section: Discussionmentioning

confidence: 99%

Compound‐specific isotope analysis of amino acids as a new tool to uncover trophic chains in soil food webs

Pollierer

Larsen

Potapov

et al. 2019

Ecological Monographs

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“…In contrast, consumers feeding on a high protein quality diet do not have to elevate their nitrogen metabolism and excretion and consequently have lower Δ 15 N. As carnivores ingest higher quality protein than herbivores, this mechanism leads to a decrease in trophic discrimination factors with an increase in trophic levels within food webs (Robbins et al 2005). These patterns are further supported by results from compound‐specific isotope analysis of amino acids (CSIA‐AA), a method using only specific compounds instead of the bulk isotopes traditionally studied (McMahon and McCarthy , Ohkouchi et al 2017, Ishikawa ). In experimental CSIA‐AA studies under controlled feeding regimes, Δ 15 N depends on diet quality, suggesting that the trophic discrimination factor in nature is more variable than previously thought (McMahon et al 2015, Chikaraishi et al 2015).…”

Section: Discussionmentioning

confidence: 86%

“…blood, liver) are usually 13 C‐depleted relative to other tissues (Focken and Becker , Pinnegar and Polunin , Pinnegar et al ), so that selective feeding on these lipid‐rich tissues may lead to lower Δ 13 C discrimination than in predators. Further effects on isotope discrimination factors, both in regard to Δ 13 C and Δ 15 N, may arise in cases where parasites do not only feed on host tissue but also on non‐host resources such as the general gut content of their hosts or on epiphytic and intestinal bacteria (Goedknegt et al ). Apart from a few parasites of medical or veterinarian importance, our knowledge of the actual feeding processes (which tissues and components are consumed), and the biochemical pathways, within various parasite taxa is very limited, and clearly deserves further investigation to help elucidate the observed variation in discrimination factors among parasite taxa.…”

Section: Discussionmentioning

confidence: 99%

Parasites and stable isotopes: a comparative analysis of isotopic discrimination in parasitic trophic interactions

Thieltges

Goedknegt

O’Dwyer³

et al. 2019

Oikos

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Stable isotopes are widely used to identify trophic interactions and to determine trophic positions of organisms in food webs. Comparative studies have provided general insights into the variation in isotopic composition between consumers and their diet (discrimination factors) in predator–prey and herbivore–plant relationships while other major components of food webs such as host–parasite interactions have been largely overlooked. In this study, we conducted a literature‐based comparative analysis using phylogenetically‐controlled mixed effects models, accounting for both parasite and host phylogenies, to investigate patterns and potential drivers in Δ13C and Δ15N discrimination factors in metazoan parasitic trophic interactions. Our analysis of 101 parasite–host pairs revealed a large range in Δ13C (–8.2 to 6.5) and Δ15N (–6.7 to 9.0) among parasite species, with no significant overall depletion or enrichment of 13C and 15N in parasites. As previously found in other trophic interactions, we identified a scaling relationship between the host isotopic value and both discrimination factors with Δ13C and Δ15N decreasing with increasing host δ13C and δ15N, respectively. Furthermore, parasite phylogenetic history explained a large fraction (>60%) of the observed variation in the Δ15N discrimination factor. Our findings suggest that the traditional isotope ecology framework (using an average Δ15N of 3.4‰) applies poorly to parasitic trophic interactions. They further indicate the need for a scaled rather than a fixed trophic discrimination factor framework along gradients of host δ15N. We also identified several conceptual and methodological issues which should to be considered in future research to help integrate parasitic interactions into a holistic isotope ecology framework across diverse trophic interactions.

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“…nitrogen isotope of amino acids) have shown potential to differentiate between autochthonous and allochthonous food resources in streams. Specifically, terrestrial plants are strongly enriched in δ 2 H compared to algae (c. 100‰ difference; Sabo, Finlay, Kennedy, & Post, 2010;Dekar, King, Back, Whigham, & Walker, 2012), even in forested headwater streams (Doucett, Marks, Blinn, Caron, & Hungate, 2007), and compound specific isotopes are not sensitive to food resource mixing (Ishikawa, 2018). These advances in isotope techniques, particularly δ 2 H in organism bulk tissue, have enabled, for the first time in the present study, to address food resource contribution in food webs of low order mountain streams and response relations with land cover alteration.…”

Section: Introductionmentioning

confidence: 99%

Catchment land cover influences macroinvertebrate food‐web structure and energy flow pathways in mountain streams

et al. 2019

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Understanding how different food resources sustain stream food webs is fundamental towards increasing our knowledge on trophic structure and energy flow pathways in fluvial ecosystems. Food webs in small mountain streams are sustained by autochthonous (instream primary production) and allochthonous (inputs from the terrestrial ecosystem) organic resources, with their relative importance highly dependent on catchment land cover. This study aimed to understand how catchment land cover determines food resource type (autochthonous, allochthonous) and quantity in mountain streams, and how this affects energy flow pathways and food web structure. We hypothesised that food resource type and quantity would reflect catchment land cover. Thus, changes in food resources would lead to shifts in macroinvertebrate assimilation of autochthonous and allochthonous food resources and consequently in dominant energy flow pathways. We further hypothesised that changes in food resources will have strong effects on dominant feeding groups and community biomass distribution among taxa in food webs. Energy flow pathways were quantified by combining macroinvertebrate biomass measures and assimilation of food resources estimated from δ2H and δ15N in 10 streams along a forest cover gradient, located in the Cantabrian Mountains (northern Spain). Results showed that grassland/shrub dominated streams had a higher proportion autochthonous food resources and a lower proportion of allochthonous food resources, whereas forested streams showed the opposite pattern. Changes in food resources with forest cover resulted in shifts in food resource assimilation and dominant energy flow pathways. Forested streams were mainly sustained by allochthonous resources, while streams flowing through grassland/shrub landscapes were mostly sustained by autochthonous resources. Food resource assimilation differed between feeding groups. Detritivores showed a fixed assimilation of allochthonous resources independent of resource quantity, while omnivore assimilation was determined by the dominant food resource. This was reflected in food‐web structure. There was an increase in detritivore biomass and conservation of omnivore biomass with increasing forest cover, leading to a more equal distribution of community biomass among macroinvertebrates comprising individual food webs. The dependence of stream food webs on dominant food resources highlights the importance of catchment land cover in determining energy flow pathways and food web structure in low order mountain streams. These findings will improve our predictions on the effects of land cover change on the functioning of mountain stream ecosystems.

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Use of compound‐specific nitrogen isotope analysis of amino acids in trophic ecology: assumptions, applications, and implications

Cited by 48 publications

References 91 publications

Compound‐specific isotope analysis of amino acids as a new tool to uncover trophic chains in soil food webs

Compound‐specific isotope analysis of amino acids as a new tool to uncover trophic chains in soil food webs

Parasites and stable isotopes: a comparative analysis of isotopic discrimination in parasitic trophic interactions

Catchment land cover influences macroinvertebrate food‐web structure and energy flow pathways in mountain streams

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