Fatty Acid Signature Analysis Research Articles

Integrating pigment and fatty acid profiles for enhanced estimation of seston community composition

AbstractClimate change, nutrition pollution, and land use alterations influence the primary production of lakes. While light‐microscopy counting remains the standard for estimating phytoplankton community composition, its expense and time‐consuming nature necessitate cost‐effective alternatives for seston analysis. Furthermore, estimating the contribution of seston constituents other than primary producers, or non‐algal particles, is not possible with light‐microscopy counting. Biotracer approach using computational methods and chemotaxonomic biomarkers such as carotenoid pigments and fatty acids have been used as an alternative in seston analysis when species‐level taxonomy is not required. However, a comprehensive testing of how well carotenoid and fatty acids can be used in estimating a wide range of seston phytoplankton communities using different estimation methods is lacking. To assess the accuracy of a suite of state‐of‐the‐art biotracer‐based computational methods, namely CHEMTAX, FASTAR (Fatty Acid Source‐Tracking Algorithm in R), MixSIAR, and QFASA (Quantitative Fatty Acid Signature Analysis), lake water samples were collected in 2016, 2018, 2019, 2020, and 2021 for seston composition analysis in a boreal eutrophic lake with light‐microscopy counting serving as the reference for seston composition. Absolute errors between the biotracer‐based estimates were calculated to evaluate method performance. A small laboratory experiment to assess the reliability of estimating the contribution of non‐algal particles using the computational methods with fatty acids was also conducted. The closest alignment to light‐microscopy counting in terms of absolute error was achieved when both carotenoids and fatty acids were used together in the QFASA method. For CHEMTAX, FASTAR, and MixSIAR, using carotenoids alone produced the closest results. Additionally, the estimation methods accurately assessed the proportion of non‐algal particles in the seston when using fatty acid profiles, a capability not possible with light‐microscopy counting. Our findings demonstrate that the biotracer approach provides a viable and cost‐effective alternative to light‐microscopy counting when group‐level information of phytoplankton community composition suffices. Furthermore, we show that non‐algal particles can be effectively estimated together with phytoplankton when using fatty acids.

Space‐use strategies drive diet composition of Baffin Bay polar bears

AbstractPolar bears (Ursus maritimus) depend on sea ice to hunt their ice‐associated prey. However, climate‐induced sea ice loss is leading to changes in space‐use strategies of polar bears, with bears in some subpopulations spending more time on land or selecting alternative habitats. One such documented alternative habitat is glacier ice, which provides year‐round access to prey, although the feeding habits of polar bears using glacier ice relative to those following the retreating ice and/or seasonally moving onshore are not known. Here, we use adipose tissue from polar bears (n = 104) from the Baffin Bay subpopulation live‐captured in Northwest Greenland during the springs of 2009–2013 to investigate dietary patterns between space‐use strategies inferred from satellite telemetry data, while considering demographic and interannual variation. Using quantitative fatty acid signature analysis (QFASA) to generate diet estimates, ringed seals (Pusa hispida) and bearded seals (Erignathus barbatus) were estimated as the primary and secondary prey of Baffin Bay polar bears for all sex/age classes and sampling years, apart from a single anomalous year (2009) with a relatively high proportion of beluga (Delphinapterus leucas) and narwhal (Monodon monoceros). While demographic and short‐term temporal variation was minimal, fatty acid signatures and QFASA‐generated diet estimates clearly differed between polar bears using coastal and offshore space‐use strategies. “Offshore” adult females (n = 31), which make long‐distance movements across the Baffin Bay pack ice, had high proportions of C22‐chain length monosaturated fatty acids and diet estimates that included beluga, narwhal, harp (Pagophilus groenlandicus), and hooded seal (Cystophora cristata). “Coastal” adult females (n = 6), which remain resident at glacier fronts in Northwest Greenland year‐round including during the sea ice‐free season, consumed proportionally more ringed seals (+13%) and similar proportions of bearded seal, but essentially no beluga and narwhal or harp and hooded seal. Thus, space‐use strategy is a driver of intrapopulation diet variability. As space‐use strategies change with ongoing loss of sea ice habitat, our results suggest important ramifications for polar bear feeding patterns.

Do catadromous thinlip grey mullet benefit from shifting to freshwater? A perspective from fatty acid signature analysis

To investigate the potential benefits of the catadromous thinlip grey mullet (Chelon ramada Risso, 1827) migration to freshwater, the total lipid content and fatty acid (FA) profile of female’s muscle and gonads caught in both the estuary and river were analyzed. The freshwater contingent presented a higher body condition, greater muscle gross energy, and larger gonads with higher lipid reserves. These animals showed a muscle profile rich in C16:1n-7 and lower LC-PUFA that contrast with the higher relative amount of C18:1n-9, n-3 FA, and unsaturated LC-PUFA, such as C18 and C20 FA found in the estuarine contingent. The gonads of both contingents showed a constant and high relative amount of polyunsaturated FAs (PUFA, 37%). However, in terms of essential fatty acids (EFAs), the estuarine contingent had a higher relative amount of C18:2n-6, C20:4n-6, C20:5n-3, and C22:6n-3. On the other hand, the freshwater contingent showed a higher relative amount of n-3 FA precursors, namely C18:3n-3, and a still low relative amount of C22:6n-3. This suggests a mismatch between the metabolic omega-3 pathway and the physiological maturity stages, similar to a phenomenon of dormancy. In this sense, not all these individuals may reproduce annually, and the later stages of gonad development will require supplementary energy derived from feeding at the estuary. Thus, freshwater migration may promote a reproductive strategy enabling adults to take advantage of the warm and food-rich summer/autumn period, adjust spawning and juvenile appearance, and reduce the population’s exposure to habitat changes and/or stochastic events.

Thiamine Deficiency M74 Developed in Salmon (Salmo salar) Stocks in Two Baltic Sea Areas after the Hatching of Large Year-Classes of Two Clupeid Species—Detected by Fatty Acid Signature Analysis

Lipid-related thiamine (vitamin B1) deficiency of Baltic salmon (Salmo salar), the M74 syndrome, is generally caused by feeding on abundant young sprat (Sprattus sprattus) in the Baltic Proper, the main foraging area of these salmon. In 2014, a strong year-class of sprat was hatched in the Baltic Proper, and a strong herring (Clupea harengus) year-class was hatched in the Gulf of Bothnia, where herring is the dominant salmon prey. The fatty acid (FA) signatures of prey fish in muscle or eggs of second sea-year spawners suggested that 27% of wild River Simojoki and 68% of reared River Dal salmon remained in the Gulf of Bothnia in 2014 instead of continuing to the Baltic Proper. In 2016, 23% of the M74 females of the River Simojoki and 58% of the River Dal originated from the Gulf of Bothnia, and 13% and 16%, respectively, originated from the Baltic Proper. Some salmon from the River Neris in the southern Baltic Proper had also been feeding in the Gulf of Bothnia. In general, low free thiamine (THIAM) concentration in eggs was associated with high lipid content and high docosahexaenoic acid (DHA, 22:6n−3) and n−3 polyunsaturated FA (n−3 PUFA) concentrations in muscle but not in eggs. A higher THIAM concentration and lower proportions of DHA and n−3 PUFAs in Arctic Ocean salmon eggs, despite higher egg lipid content, indicated that their diet contained fewer fatty fish than the Baltic salmon diet. Hence, M74 originated by foraging heavily on young fatty sprat in the Baltic Proper or herring in the Gulf of Bothnia.

Integrated approach for the isotope trophic position of black-tailed gull (Larus crassirostris) eggs over a decade: Combining stable isotopes of amino acids and fatty acids composition

Recently, compound-specific isotope analysis (CSIA) using the amino acid nitrogen stable isotope ratio (δ15NAAs) has been widely used for accurate estimation of trophic position (TP). In addition, a quantitative fatty acid signature analysis (QFASA) offers insights into diet sources. In this study, we used these techniques to estimate the TP for seabirds that rely on diverse food sources across multiple ecosystems. This allows for the proper combination of factors used in TP calculation which are different for each ecosystem. The approach involved the application of a multi-mixing trophic discrimination factor (TDF) and mixing β which is a Δδ15N between trophic and source amino acid of primary producer. Since the black-tailed gulls (BTGs) are income-breeding seabirds, which rely on energy sources obtained around their breeding sites, they and their eggs could be useful bioindicators for environmental monitoring. However, the ecological properties of BTGs such as habitats, diets, and TP are not well known due to their large migration range for wintering or breeding and their feeding habits on both aquatic and terrestrial prey. In this study, the eggs were used for estimating TP and for predicting TP of mother birds to overcome difficulties such as capturing birds and collecting non-invasive tissue samples. Eggs, sampled over a decade from three Korean islands, showed spatial differences in diet origin. Considering both the food chain and physiology of BTG, the TP of eggs was estimated to be 3.3–4.0. Notably, the TP was significantly higher at site H (3.8 ± 0.1) than at site B (3.5 ± 0.2), which indicated a higher contribution of marine diet as confirmed by QFASA. Using a reproductive shift of δ15NAAs, the TP of the mother birds was predicted to be 3.6–4.3, positioning them as the top predator in the food web. The advanced integration of multiple approaches provides valuable insights into bird ecology.

Varying Diet Composition Causes Striking Differences in Legacy and Emerging Contaminant Concentrations in Killer Whales across the North Atlantic.

Lipophilic persistent organic pollutants (POPs) tend to biomagnify in food chains, resulting in higher concentrations in species such as killer whales (Orcinus orca) feeding on marine mammals compared to those consuming fish. Advancements in dietary studies include the use of quantitative fatty acid signature analysis (QFASA) and differentiation of feeding habits within and between populations of North Atlantic (NA) killer whales. This comprehensive study assessed the concentrations of legacy and emerging POPs in 162 killer whales from across the NA. We report significantly higher mean levels of polychlorinated biphenyls (PCBs), organochlorine pesticides, and flame retardants in Western NA killer whales compared to those of Eastern NA conspecifics. Mean ∑PCBs ranged from ∼100 mg/kg lipid weight (lw) in the Western NA (Canadian Arctic, Eastern Canada) to ∼50 mg/kg lw in the mid-NA (Greenland, Iceland) to ∼10 mg/kg lw in the Eastern NA (Norway, Faroe Islands). The observed variations in contaminant levels were strongly correlated with diet composition across locations (inferred from QFASA), emphasizing that diet and not environmental variation in contaminant concentrations among locations is crucial in assessing contaminant-associated health risks in killer whales. These findings highlight the urgency for implementing enhanced measures to safely dispose of POP-contaminated waste, prevent further environmental contamination, and mitigate the release of newer and potentially harmful contaminants.

Biomagnification and elimination effects of persistent organic pollutants in a typical wetland food web from South China

This study investigated the quantitative sources of persistent organic pollutants (POPs), their biomagnification factors, and their effect on POP biomagnification in a typical waterbird (common kingfisher, Alcedo atthis) food web in South China. The median concentrations of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in kingfishers were 32,500 ng/g lw and 130 ng/g lw, respectively. The congener profiles of PBDEs and PCBs showed significant temporal changes because of the restriction time points and biomagnification potential of different contaminants. The concentrations of most bioaccumulative POPs, such as CBs 138 and 180 and BDEs 153 and 154, decreased at lower rates than those of other POPs. Pelagic fish (metzia lineata) and benthic fish (common carp) were the primary prey of kingfishers, as indicated by quantitative fatty acid signature analysis (QFASA) results. Pelagic and benthic prey species were the primary sources of low and high hydrophobic contaminants for kingfishers, respectively. Biomagnification factors (BMFs) and trophic magnification factors (TMFs) had parabolic relationships with log KOW, with peak values of approximately 7. Significant negative correlations were found between the whole-body elimination rates of POPs in waterbirds and the log-transformed TMFs and BMFs, indicating that the strong metabolism of waterbirds could potentially affect POP biomagnification.

Factors influencing egg thiamine concentrations of Lake Ontario lake trout: 2019–2020

In the Great Lakes region, thiamine deficiency is considered a recruitment bottleneck for lake trout Salvelinus namaycush and has been correlated with the consumption of non-native alewife Alosa pseudoharengus. While alewife, the most abundant forage fish in Lake Ontario, are the predominant prey for lake trout, they also consume benthic prey such as round goby Neogobius melanostomus. Because variation in the proportion of alewife in lake trout diets is linked to variation in egg thiamine concentrations, understanding how factors such as region of capture and hatchery-strain of lake trout influence diet, are key to understanding the patterns of variation in egg thiamine concentrations observed in this species. With recent increases in natural recruitment of lake trout being observed in the western region of the lake, understanding if egg thiamine is a potential driver is crucial to the rehabilitation of lake trout. In this study, we evaluated egg thiamine concentrations in lake trout during 2019–2020. We found no significant difference in egg thiamine concentrations among regions. However, a stocked Lake Superior deepwater morphotype (Superior Klondike Wild – SKW) showed significantly higher egg thiamine concentrations compared to the lean morphotype including Seneca (SEN) and Lake Champlain Domestic (LCD) strains. An analysis of fatty acid signatures of each hatchery-strain suggested that the SKW strain consumed a higher proportion of round goby than lean strains. Overall, these results suggest that morphotypic differences in the feeding ecology of lake trout can result in biochemical changes which may influence the effectiveness of restoration efforts.

Quantitative fatty acid signature analysis reveals a high level of dietary specialization in killer whales across the North Atlantic.

Quantifying the diet composition of apex marine predators such as killer whales (Orcinus orca) is critical to assessing their food web impacts. Yet, with few exceptions, the feeding ecology of these apex predators remains poorly understood. Here, we use our newly validated quantitative fatty acid signature analysis (QFASA) approach on nearly 200 killer whales and over 900 potential prey to model their diets across the 5000 km span of the North Atlantic. Diet estimates show that killer whales mainly consume other whales in the western North Atlantic (Canadian Arctic, Eastern Canada), seals in the mid-North Atlantic (Greenland), and fish in the eastern North Atlantic (Iceland, Faroe Islands, Norway). Nonetheless, diet estimates also varied widely among individuals within most regions. This level of inter-individual feeding variation should be considered for future ecological studies focusing on killer whales in the North Atlantic and other oceans. These estimates reveal remarkable population- and individual-level variation in the trophic ecology of these killer whales, which can help to assess how their predation impacts community and ecosystem dynamics in changing North Atlantic marine ecosystems. This new approach provides researchers with an invaluable tool to study the feeding ecology of oceanic top predators.

Herbivorous cladoceran essential fatty acid and cholesterol content across a phosphorous and DOC gradients of boreal lakes—Importance of diet selection

Abstract Eutrophication has been shown to increase production of nutritionally low‐quality cyanobacteria and decrease the long‐chain polyunsaturated fatty acid (PUFA) content of seston. Contrarily, lake browning inhibits cyanobacteria contribution in seston and favours poorly grazable mixotrophic algal species. These environmental changes have probable impacts on the diet and long‐chain PUFA content of primary consumers. However, herbivorous zooplankton may preferentially retain PUFAs through diet selection for optimal growth and reproduction, but such selective feeding is challenging to document in nature owing to the difficulties in quantifying zooplankton diet. Here, we sampled seston and herbivorous cladocerans (Daphnia sp. and Bosmina sp.) from lakes (n = 23) in Finland along eutrophication (total phosphorous) and browning gradients (dissolved organic carbon [DOC]). We analysed the fatty acid content of seston (mg FA/g POC [particular organic content]) and cladocerans (mg FA/g C), and estimated available and consumed diet biomass percentages with quantitative fatty acid signature analysis. Cladoceran diet preference was evaluated as the difference between consumed and available food sources, to understand if they preferentially retain high nutritional quality diet. Generally, lake chemistry and morphometry poorly explained seston and cladoceran long‐chain PUFA contents. However, multiple linear models for shorter chain PUFAs (linoleic acid [LA] and alpha‐linolenic acid [ALA]) performed better in explaining variation in the LA and ALA content of seston (20% and 11%) and cladocerans (36% and 46%, respectively). The factors most strongly and positively associated with the LA and ALA content of seston and cladocerans were phosphorus and DOC concentrations, respectively. Seston and cladoceran PUFA contents were clearly uncorrelated. In most of the sampled lakes, high‐quality diet (i.e., diatoms and cryptomonads) was preferred by cladocerans and low‐quality diet (cyanobacteria) was avoided. Lake chemistry poorly explained cladoceran diet preference, but high‐quality preference was positively associated with lake average depth. In summary, our space‐for‐time study approach did not reveal that eutrophication or browning downgraded the seston nor cladoceran PUFA quality. We found no correlation with seston and cladoceran PUFA content, but a clear mismatch between available and consumed diet. Our results suggest a selective feeding strategy of cladocerans, possibly through foraging in high‐quality algae patches or selective assimilation of PUFAs.

Measuring repeatability of compositional diet estimates: Anexample using quantitative fatty acid signature analysis.

By measuring the temporal consistency, or repeatability, in the diets of predators, we can gain a better understanding of the degree of individual specialization in resource utilization and implications for predator–prey interactions, population dynamics, and food web structure. To measure repeatability, we require repeated diet estimates of individuals over time, such as those derived from quantitative fatty acid signature analysis (QFASA), a popular diet estimation technique. However, diet estimates are often lengthy compositional vectors with many zeros, as some prey will not be consumed by all individuals, precluding the use of previously proposed measures of repeatability. In this paper, we propose a novel approach for inferring repeatability for multivariate data and, in particular, compositional diet estimates. We extend the commonly used measure of repeatability for univariate data to the multivariate compositional setting by utilizing the mean squares obtained from a nonparametric multivariate analysis of variance, and an appropriate choice of statistical distance. Our measure and its extension are compatible with both balanced and unbalanced data sets. Associated confidence intervals via nonparametric bootstrapping are also developed for the case of QFASA diet estimates that incorporate both sampling error and measurement error, where the latter error arises because the diets of predators are estimated. Simulation study results suggest that for practical levels of repeatability, our methods yield confidence intervals with the desired coverage probability even when the sample size relative to the dimension of the data (i.e., number of prey species eaten) is small. We tested our methods using QFASA diet estimates for free‐ranging Northwest Atlantic grey seals. Given the importance of understanding how predator diets vary over time and space, our method may find broad application to other compositional diet estimates, including those derived from the stomach or fecal contents, and stable isotope analyses.

Biomagnification of Persistent Organic Pollutants from Terrestrial and Aquatic Invertebrates to Songbirds: Associations with Physiochemical and Ecological Indicators.

Biomagnification of persistent organic pollutants (POPs) is affected by physiochemical properties of POPs and ecological factors of wildlife. In this study, influences on species-specific biomagnification of POPs from aquatic and terrestrial invertebrates to eight songbird species were investigated. The median concentrations of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in birds were 175 to 13 200 ng/g lipid weight (lw) and 62.7 to 3710 ng/g lw, respectively. Diet compositions of different invertebrate taxa for songbird species were quantified by quantitative fatty acid signature analysis. Aquatic insects had more contributions of more hydrophobic POPs, while terrestrial invertebrates had more contributions of less hydrophobic PCBs in songbirds. Biomagnification factors (BMFs) and trophic magnification factors had parabolic relationships with log KOW and log KOA. The partition ratios of POPs between bird muscle and air were significantly and positively correlated with log KOA of POPs, indicating respiratory elimination as an important determinant in biomagnification of POPs in songbirds. In this study, the species-specific biomagnification of POPs in songbird species cannot be explained by stable isotopes of carbon and nitrogen and body parameters of bird species. BMFs of most studied POPs were significantly correlated with proportions of polyunsaturated fatty acids in different species of songbirds.

Validation of quantitative fatty acid signature analysis for estimating the diet composition of free-ranging killer whales

Accurate diet estimates are necessary to assess trophic interactions and food web dynamics in ecosystems, particularly for apex predators like cetaceans, which can regulate entire food webs. Quantitative fatty acid analysis (QFASA) has been used to estimate the diets of marine predators in the last decade but has yet to be implemented on free-ranging cetaceans, from which typically only biopsy samples containing outer blubber are available, due to a lack of empirically determined calibration coefficients (CCs) that account for fatty acid (FA) metabolism. Here, we develop and validate QFASA for killer whales using full blubber from managed-care and free-ranging individuals. First, we compute full, inner, and outer blubber CCs from the FA signatures across the blubber layers of managed-care killer whales and their long-term diet items. We then run cross-validating simulations on the managed-care individuals to evaluate the accuracy of diet estimates by comparing full-depth and depth-specific estimates to true diets. Finally, we apply these approaches to subsistence-harvested killer whales from Greenland to test the utility of the method for free-ranging killer whales, particularly for the outer blubber. Accurate diet estimates for the managed-care killer whales were only achieved using killer whale-specific and blubber-layer-specific CCs. Modeled diets for the Greenlandic killer whales largely consisted of seals (75.9 ± 4.7%) and/or fish (20.4 ± 2.4%), mainly mackerel, which was consistent with stomach content data and limited literature on this population. Given the remote habitats and below surface feeding of most cetaceans, this newly developed cetacean-specific QFASA method, which can be applied to outer-layer biopsies, offers promise to provide a significant new understanding of diet dynamics of free-ranging odontocetes and perhaps other cetacean species throughout the world’s oceans.

Occurrence and Distribution of Persistent Organic Pollutants (POPs) in Amphibian Species: Implications from Biomagnification Factors Based on Quantitative Fatty Acid Signature Analysis.

Contaminants pose a great threat to amphibian populations, but the bioaccumulation and distribution of contaminants in amphibians are still unclear. Polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) had median concentrations of 468-3560 ng/g lipid weight (lw) and 206-2720 ng/g lw in the muscle of amphibians, respectively. BDE 209 was the predominant PBDE congener, while CBs 118, 138, 153, and 180 were the main PCB congeners. The diet compositions of amphibians were estimated by quantitative fatty acid signature analysis (QFASA). Dragonfly contributed the most to the diet of amphibians. Biomagnification factors (BMFs) based on quantitative amphibian/insect relationships showed more credible results than BMFs based on amphibian/each insect or amphibian/combined prey relationships. BMFs derived from QFASA declined with log KOW from 5 to 6.5 and then showed a parabolic relationship with log KOW greater than 6.5. BMFs of PCBs were significantly influenced by the elimination capacity of PCBs in amphibians. Less-hydrophobic PCBs preferentially accumulated in the skin than in muscle, which was probably due to the dermal exposure of less-hydrophobic PCBs for amphibians. The biomagnification and distribution of contaminants may be affected by multiple exposure pathways and the toxicokinetics of contaminants in various life stages of amphibians.

Fecal DNA metabarcoding shows credible short-term prey detections and explains variation in the gut microbiome of two polar bear subpopulations

This study developed and evaluated DNA metabarcoding to identify the presence of pinniped and cetacean prey DNA in fecal samples of East Greenland (EG) and Southern Beaufort Sea (SB) polar bears Ursus maritimus sampled in the spring of 2015-2019. Prey DNA was detected in half (49/92) of all samples, and when detected, ringed seal Pusa hispida was the predominant prey species, identified in 100% (22/22) of EG and 81% (22/27) of SB polar bear samples with prey DNA detected. Bearded seal Erignathus barbatus DNA was found in 19% (5/27) of SB polar bear samples for which prey DNA was detected. Prey DNA detection frequencies and relative abundances were compared to estimates from quantitative fatty acid signature analysis (QFASA) for a subset of SB polar bears. Ringed seal and bearded seal were the main prey identified by both methods, but QFASA also identified 2 cetacean prey species not found by prey DNA. Differences in DNA metabarcoding vs. QFASA results were likely related to the different dietary timescales captured by each approach, i.e. short-term vs. long-term diet, respectively. Prey DNA detection, sex/age class, and subpopulation significantly explained variation in polar bear gut bacterial composition. Polar bear samples with prey DNA detected were associated with higher abundances of the bacterial classes Clostridia and Bacilli and lower abundances of Negativicutes. Fecal DNA metabarcoding is thus useful for identifying recent prey of polar bears, complementing quantitative and likely longer-term QFASA estimates, and may help understand variation in the polar bear gut microbiome.

First evaluation of quantitative fatty acid signature analysis (QFASA) in dolphins

Accurate diet estimation of marine mammals is fundamental to investigate their ecological roles in marine habitats, but it remains a pervasive challenge to researchers due to the constraints associated with conventional methods based on stomach contents or feces analysis, which are imprecise, limited to last meal and often biased. Quantitative fatty acid signature analysis (QFASA), an emerging method for diet estimations, has been demonstrated to be reliable in reconstructing long-term diets of many marine mammal predators; however, its application has not been seriously evaluated in dolphins. To this end, we compared the QFASA estimates obtained using 8 pre-existing calibration coefficient sets, 3 fatty acid subsets, and 3 prey library subsets to the true diet of a captive Indo-Pacific humpback dolphin (Sousa chinensis) that was fed a long-term diet of mostly gizzard shad (Clupanodon thrissa) with smaller proportions of Japanese seabass (Lateolabrax japonicus), pumpkinseed (Lepomis gibbosus), roughscale tonguesole (Cynoglossus lida), and Chinese herring (Ilisha elongate). The diet of the dolphin was best reconstructed using the calibration coefficients derived from captive feeding trials of American mink (Mustela vison) that were fed herring with the “main” fatty acid subset; this process correctly identified gizzard shad as the main prey source of the dolphin with the highest actual diet proportions and lowest predator signature proportions outside the range of the mean prey proportions. In addition, high accuracy and consistency were acquired in the diet estimations obtained using the calibration coefficients derived from minks fed herring and herring plus seal oil even though pseudo-prey were included in our model, revealing the high robustness and reliability of QFASA in reconstructing the dolphin diet. We recommend caution in selecting fatty acid subsets when using fatty acid signatures derived from different studies. Overall, QFASA offers a promising tool to quantify the long-term diets of humpback dolphins and other odontocetes.

Quantitative fatty acid signature analysis (QFASA) in indoor dust: Implication for tracking indoor source accumulation of organic pollutant exposure.

Indoor dust has been used as a proxy for estimating human indoor pollutant exposure risks, yet source identification remains challenging. This study tentatively investigated whether quantitative fatty acid signature analysis (QFASA) of dust, could be applied to indicate sources and their respective contributions for a major class of indoor organic pollutants organophosphate flame retardants (OPFRs). We observed significant correlations between OPFR concentrations and lipid content (p<0.05) in house dusts. Using 15 signature fatty acids (FAs) in various indoor sources and the QFASA model, we found that clothing (39.1% in Australia and 36.5% in China) was the predominant contributing vector of dust OPFR followed by cooking oil and pet hair. Among these sources, clothing materials were proposed to be important vectors introducing organic pollutants to the indoor environment. Our QFASA contribution estimation analyses allowed for accurate prediction of most OPFR concentrations in clothing, validating our findings that clothing materials may serve as important carrier for OPFRs in indoor migration. This is the first study attempting to identify sources of organic pollutants using QFASA in an indoor setting and will provide important insight into the transfer of organic pollutants in indoor environment.

Assessing the Reliability of Quantitative Fatty Acid Signature Analysis and Compound-Specific Isotope Analysis-Based Mixing Models for Trophic Studies.

The study of the trophic relationships of aquatic animals requires correct estimates of their diets. We compared the quantitative fatty acid signature analysis (QFASA) and the isotope-mixing model IsoError, based on the compound-specific isotope analysis of fatty acids (CSIA-FA), which are potentially effective models for quantitative diet estimations. In a 21-day experiment, Daphnia was fed a mixture of two food items, Chlorella and Cryptomonas, which were supplied in nearly equal proportions. The percentages and isotope values of the FAs of the algal species and Daphnia were measured. The IsoError based on CSIA-FA gave an estimation of algae consumption using only one FA, 18:3n-3. According to this model, the proportion of consumption of Chlorella decreased while the proportion of consumption of Cryptomonas increased during the experiment. The QFASA model was used for two FA subsets—the extended-dietary subset, which included sixteen FAs, and the dietary one, which included nine FAs. According to both subsets, the portion of consumed Chlorella decreased from Day 5 to 10 and then increased at Day 21. The comparison of the two model approaches showed that the QFASA model is a more reliable method to determine the contribution of different food sources to the diet of zooplankton than the CSIA-based mixing model.

Polar bear diet composition reveals spatiotemporal distribution of Arctic marine mammals across Nunavut, Canada

Climate warming and associated physical and biological changes will likely force widespread species redistribution, particularly in polar environments. However, tracking such distributional shifts is difficult. The dietary habits of apex predators, like polar bears (Ursus maritimus), may provide early signals of distributional change in prey populations. We used harvest-based sampling to investigate the spatial feeding patterns of polar bears across Nunavut from 2010 to 2018 (n = 1570) and identify spatiotemporal clusters of different prey based on predator diet estimates. Quantitative fatty acid signature analysis and the Getis-Ord Gi* statistic identified spatial clusters of high or low dietary proportions (i.e., “hot spots” and “cold spots”) reflecting seasonal and spatial availability of prey. Ringed seal (Pusa hispida) was the primary prey of bears throughout Nunavut followed by bearded seal (Erignathus barbatus), although proportional consumption varied spatially. A consistent ringed seal consumption hot spot was found in Gulf of Boothia indicating the importance of year-round availability of ringed seals. Spatial clusters of bearded seal and Atlantic walrus (Odobenus rosmarus rosmarus) throughout Foxe Basin suggested overlapping seasonal distributions and high regional abundance. Bears had consistently high dietary levels of harbour seal (Phoca vitulina) around Southampton Island and along the western coast of Hudson Bay suggesting a possible year-round concentration of this prey. Hot spots of harp seal (Pagophilus groenlandicus) consumption were evident throughout Davis Strait and a spring-summer hot spot around Jones Sound was consistent with harp seal migratory patterns. Year-round beluga whale (Delphinapterus leucas) hot spots were found along eastern Baffin Island and southern Viscount Melville Sound providing new knowledge of local conditions that promote polar bear predation or scavenging. Narwhal (Monodon monoceros) were less susceptible to predation with only one spatial cluster of high consumption appearing during spring-summer in Barrow Strait. Bowhead whale (Balaena mysticetus) hot spots occurred around south-western Foxe Basin and seasonally in southern Viscount Melville Sound suggesting carcasses are locally accessible to bears and may act as a supplemental food source in particular areas and seasons. The congruence of polar bear feeding habits and known prey distribution suggests polar bears serve as ecological indicators and ongoing monitoring of their diets may reveal regional and broad-scale changes in prey population distributions and Arctic ecosystem functioning.

Improving the application of quantitative fatty acid signature analysis in soil food webs: The effects of diet fat content.

Quantitative fatty acid signature analysis (QFASA) as a biochemical tool to study the diet composition of predators is frequently used in marine ecology to infer trophic links in vertebrate consumers. However, the potential and challenges of this method in other ecosystems have only recently been studied. The application in soil ecosystems leads to hurdles not encountered in the marine, such as the low similarity of fatty acid signatures between resource and consumer. So far, diet estimation attempts have been semisuccessful, necessitating to adapt QFASA for use in soil food webs. Dietary fat content may play an important role, as it influences consumer metabolism, and thus calibration coefficients for fatty acid trophic transfer. A series of feeding trials with baker's yeast spiked with five different pure fatty acids at various concentrations was conducted with Collembola, and the changes in calibration coefficients were observed. From there, equations were gained through regression analysis and new sets of calibration coefficients were calculated. QFASA was applied on a range of basal resources and the results compared with previously defined calibration coefficients. Calibration coefficients changed with the proportion of fatty acids in the diet and differed between the three Collembolan species. The re‐estimation of diets showed an improvement of model performance by the new calibration coefficients and indicated several modes of fatty acid assimilation. These greatly influence the outcome of diet estimation, for example, algal and bacterial diets are likely underestimated due to high metabolic turnover rates. The application of QFASA in soil ecosystems remains challenging. The variation in calibration coefficients and the resulting decrease in estimation deviation indicate the merit of calculating calibration coefficients from consumer signatures through linear or exponential equations. Ideally, the method should, when extended to the entire fatty acid signature, allow correct determination of consumer diets in soil food webs.