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Gurney KEB, Classen HL, Clark RG. Testing for effects of growth rate on isotope trophic discrimination factors and evaluating the performance of Bayesian stable isotope mixing models experimentally: A moment of truth? PLoS One 2024; 19:e0304495. [PMID: 38875228 PMCID: PMC11178173 DOI: 10.1371/journal.pone.0304495] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2024] [Accepted: 05/13/2024] [Indexed: 06/16/2024] Open
Abstract
Discerning assimilated diets of wild animals using stable isotopes is well established where potential dietary items in food webs are isotopically distinct. With the advent of mixing models, and Bayesian extensions of such models (Bayesian Stable Isotope Mixing Models, BSIMMs), statistical techniques available for these efforts have been rapidly increasing. The accuracy with which BSIMMs quantify diet, however, depends on several factors including uncertainty in tissue discrimination factors (TDFs; Δ) and identification of appropriate error structures. Whereas performance of BSIMMs has mostly been evaluated with simulations, here we test the efficacy of BSIMMs by raising domestic broiler chicks (Gallus gallus domesticus) on four isotopically distinct diets under controlled environmental conditions, ideal for evaluating factors that affect TDFs and testing how BSIMMs allocate individual birds to diets that vary in isotopic similarity. For both liver and feather tissues, δ13C and δ 15N values differed among dietary groups. Δ13C of liver, but not feather, was negatively related to the rate at which individuals gained body mass. For Δ15N, we identified effects of dietary group, sex, and tissue type, as well as an interaction between sex and tissue type, with females having higher liver Δ15N relative to males. For both tissues, BSIMMs allocated most chicks to correct dietary groups, especially for models using combined TDFs rather than diet-specific TDFs, and those applying a multiplicative error structure. These findings provide new information on how biological processes affect TDFs and confirm that adequately accounting for variability in consumer isotopes is necessary to optimize performance of BSIMMs. Moreover, results demonstrate experimentally that these models reliably characterize consumed diets when appropriately parameterized.
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Affiliation(s)
- Kirsty E B Gurney
- Science and Technology Branch, Environment and Climate Change Canada, Saskatoon, Saskatchewan, Canada
| | - Henry L Classen
- College of Agriculture and Bioresources, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - Robert G Clark
- Science and Technology Branch, Environment and Climate Change Canada, Saskatoon, Saskatchewan, Canada
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2
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Evans TM, Beharie S. Are lipids always depleted? Comparison of hydrogen, carbon, and nitrogen isotopic values in the muscle and lipid of larval lampreys. PLoS One 2024; 19:e0286535. [PMID: 38206962 PMCID: PMC10783746 DOI: 10.1371/journal.pone.0286535] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2022] [Accepted: 05/18/2023] [Indexed: 01/13/2024] Open
Abstract
Stable isotope ratios in organisms can be used to estimate dietary source contributions, but lipids must first be accounted for to interpret values meaningfully. Lipids are depleted in heavy isotopes because during lipid synthesis light isotopes of carbon (12C) and hydrogen (1H) are preferentially incorporated. Prior work in larval lampreys has noted unusual lipid effects, which suggest lipids are enriched in the heavy isotope of carbon (13C), but still depleted in the heavy isotope of hydrogen (deuterium; 2H); nitrogen, a relatively rare element in lipids, has not been identified as being as sensitive to lipid content. Our objective was to determine if stable isotope ratios of hydrogen, carbon, and nitrogen behaved as expected in larval lampreys, or if their lipids presented different isotopic behavior. The δ2H, δ13C, and δ15N were measured from the muscle of four lamprey species before and after lipid extraction. In addition, muscle of least brook lamprey (Lampetra aepyptera) was collected every three months for a year from two streams in Maryland. Isotopic ratios were measured in bulk and lipid-extracted muscles, as well as in extracted lipids. The difference between muscle samples before and after lipid extraction (Δδ2H, Δδ13C, Δδ15N) was positively related to lipid proxy (%H or C:N ratio) and were fit best by linear models for Δδ2H and Δδ15N, and by a non-linear model for Δδ13C. The difference between lipid-extracted muscle and lipid δ13C (ΔMLδ13C) was negative and varied between months (ANOVA, F3,53 = 5.05, p < 0.005). Our work suggests that while lipids are often depleted in 13C, this is not a universal rule; however, the depletion of 2H in lipid synthesis appears broadly true.
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Affiliation(s)
- Thomas M. Evans
- Biology Department, St. Mary’s College of Maryland, St. Mary’s City, Maryland, United States of America
| | - Shale Beharie
- Biology Department, St. Mary’s College of Maryland, St. Mary’s City, Maryland, United States of America
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3
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Sardenne F, Raynon T, Munaron JM, van der Lingen CD, Sadio O, Diop K, Brosset P, Lebigre C, Soudant P, Vagner M, Pecquerie L. Lipid-correction models for δ 13C values across small pelagic fishes (Clupeiformes) from the Atlantic Ocean. MARINE ENVIRONMENTAL RESEARCH 2023; 192:106213. [PMID: 37783159 DOI: 10.1016/j.marenvres.2023.106213] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/25/2023] [Revised: 09/22/2023] [Accepted: 09/26/2023] [Indexed: 10/04/2023]
Abstract
The interpretation of δ13C values in trophic ecology requires standardization of the lipid content of organisms estimated through their C:N ratio. To avoid time-consuming lipid extractions, the use of mathematical corrections has been developed for many years, and the conclusions generally point in the direction of species-specific adjustment of the models. This study aimed at defining the maximum taxonomic level required to obtain the best corrected δ13C values in small pelagic fish of the order Clupeiformes. δ13C values of six species were analyzed bulk and lipid-free, and were used to fit and validate linear and mass-balance models at different taxonomic levels. Despite a species effect combined with the C:N ratio effect, the corrected δ13C values produced by a global model for the Clupeiformes were as good as or better when compared to lipid-free samples than those produced by species-specific models, paving the way for possible generalization to other species in this order. At the order level, the linear model outperformed the mass-balance model.
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Affiliation(s)
- Fany Sardenne
- IRD, Univ Brest, CNRS, Ifremer, LEMAR, F-29280, Plouzané, France.
| | - Thomas Raynon
- IRD, Univ Brest, CNRS, Ifremer, LEMAR, F-29280, Plouzané, France
| | | | - Carl D van der Lingen
- Department of Forestry, Fisheries and the Environment (DFFE), Cape Town, South Africa
| | - Oumar Sadio
- IRD, Univ Brest, CNRS, Ifremer, LEMAR, Dakar, Senegal
| | - Khady Diop
- IRD, Univ Brest, CNRS, Ifremer, LEMAR, Dakar, Senegal
| | - Pablo Brosset
- UMR DECOD, Ifremer, INRAE, L'Institut Agro, Plouzané, France
| | | | - Philippe Soudant
- IRD, Univ Brest, CNRS, Ifremer, LEMAR, F-29280, Plouzané, France
| | - Marie Vagner
- IRD, Univ Brest, CNRS, Ifremer, LEMAR, F-29280, Plouzané, France
| | - Laure Pecquerie
- IRD, Univ Brest, CNRS, Ifremer, LEMAR, F-29280, Plouzané, France
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4
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Cloyed CS, Johnson C, DaCosta KP, Clance LR, Russell ML, Díaz Clark C, Hieb EE, Carmichael RH. Effects of tissue decomposition on stable isotope ratios and implications for use of stranded animals in research. Ecosphere 2023. [DOI: 10.1002/ecs2.4385] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/10/2023] Open
Affiliation(s)
- Carl S. Cloyed
- Dauphin Island Sea Lab Dauphin Island Alabama USA
- Department of Marine Science University of South Alabama Mobile Alabama USA
| | | | - Kayla P. DaCosta
- Dauphin Island Sea Lab Dauphin Island Alabama USA
- Department of Marine Science University of South Alabama Mobile Alabama USA
| | - Lauren R. Clance
- Dauphin Island Sea Lab Dauphin Island Alabama USA
- Department of Marine Science University of South Alabama Mobile Alabama USA
| | | | | | | | - Ruth H. Carmichael
- Dauphin Island Sea Lab Dauphin Island Alabama USA
- Department of Marine Science University of South Alabama Mobile Alabama USA
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Riverón S, Raoult V, Slip DJ, Harcourt RG. Lipid extraction has tissue-dependent effects on isotopic values (δ 34 S, δ 13 C, and δ 15 N) from different marine predators. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2022; 36:e9346. [PMID: 35737589 PMCID: PMC9539579 DOI: 10.1002/rcm.9346] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/06/2022] [Revised: 05/31/2022] [Accepted: 06/22/2022] [Indexed: 06/15/2023]
Abstract
RATIONALE The use of sulfur isotopes to study trophic ecology in marine ecosystems has increased in the past decade. Unlike other commonly used isotopes (e.g., carbon), sulfur can better discriminate benthic and pelagic productivity. However, how lipid extraction affects sulfur isotopic values has not been assessed, despite its frequent use to remove lipid effects on δ13 C values. METHODS We used white muscle and liver samples from two species of sharks and skin samples from two species of pinnipeds (sea lion and fur seal) to assess the effects of lipid extraction on stable isotope values for δ34 S, δ13 C, and δ15 N. Isotopic values were determined using a continuous flow-isotope ratio mass spectrometer coupled to an elemental analyzer. RESULTS Lipid extraction significantly decreased δ34 S values in shark tissues, more so for liver than muscle (-4.6 ± 0.9‰ vs -0.8 ± 0.3‰, average change), with nearly no change in their standard deviations. Lipid extraction did not affect δ34 S values from pinniped skin samples (0.2 ± 0.8‰, average change). After lipid extraction, consistent increases in δ13 C values (0.2‰-7.3‰) were detected as expected, especially in tissue with high lipid content (C:N >4). After lipid extraction, significant increases in δ15 N values (0.5‰-1.4‰) were found in shark muscle and liver tissues. For pinniped skin samples, δ15 N values were not significantly lower after lipid extraction (-0.4‰ to -0.1‰). CONCLUSIONS Lipid extraction did not have a strong impact on δ34 S values of shark muscle and pinniped skin (≤1‰). However, our results suggest it is essential to consider the effects of lipid extraction when interpreting results from δ34 S values of shark liver tissue, as they significantly depleted values relative to bulk tissue (~5‰). This may reflect selective removal of sulfolipids and glutathione present in higher concentrations in the liver than in muscle and skin and requires further investigation.
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Affiliation(s)
- Sabrina Riverón
- Marine Predator Research Group, School of Natural SciencesMacquarie UniversitySydneyNew South WalesAustralia
| | - Vincent Raoult
- School of Environmental and Life SciencesUniversity of NewcastleOurimbahNew South WalesAustralia
- Marine Ecology GroupSchool of Natural SciencesMacquarie UniversitySydneyNew South WalesAustralia
| | - David J. Slip
- Marine Predator Research Group, School of Natural SciencesMacquarie UniversitySydneyNew South WalesAustralia
- Taronga Institute of Science and LearningTaronga Conservation Society AustraliaSydneyNew South WalesAustralia
| | - Robert G. Harcourt
- Marine Predator Research Group, School of Natural SciencesMacquarie UniversitySydneyNew South WalesAustralia
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Li Z, Wang S, Nie X, Sun Y, Ran F. The application and potential non-conservatism of stable isotopes in organic matter source tracing. THE SCIENCE OF THE TOTAL ENVIRONMENT 2022; 838:155946. [PMID: 35569649 DOI: 10.1016/j.scitotenv.2022.155946] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/22/2022] [Revised: 05/10/2022] [Accepted: 05/10/2022] [Indexed: 06/15/2023]
Abstract
Organic matter (OM) tracing is critical for understanding the processes of soil redistribution and global carbon cycling. It effectively supports ecological management and global climate change prediction. Stable isotopes are generally more source-specific compared with other tracers and identify OM sources with a higher level of accuracy. Nevertheless, stable isotopes may be enriched or depleted by physical and biochemical processes such as selective migration of particles and OM mineralization in transport and sedimentary environments, making it difficult to establish links between the source and sink regions. Literature on OM source identification tends to assume a direct link between stable isotope sources and sinks, ignoring the non-conservatism of stable isotopes. There is further literature on understanding and modeling the processes that link the sources to sinks in terms of the non-conservatism of stable isotopes. The disagreement in response to the non-conservatism lies in the lack of comprehensive understanding of stable isotope fingerprinting systems and non-conservatism. The development of stable isotope fingerprinting technology is full of challenges. This review outlines the applicability of stable isotope tracers, identification mechanisms, and associated quantitative models, intending to improve the stable isotope fingerprinting system. We highlight the non-conservatism of stable isotopes in space and time caused by physical and biochemical processes. Additionally, a decision tree is established to determine the quantitative tools, evaluation indicators, and procedures related to non-conservatism. This decision tree clarifies the process from non-conservatism detection to threshold determination of statistical quantification, which can guide the end-users to better apply stable isotope to trace OM sources.
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Affiliation(s)
- Zhongwu Li
- College of Geographic Sciences, Hunan Normal University, Changsha 410081, China; College of Environmental Science and Engineering, Hunan University, Changsha 410082, China
| | - Shilan Wang
- College of Geographic Sciences, Hunan Normal University, Changsha 410081, China
| | - Xiaodong Nie
- College of Geographic Sciences, Hunan Normal University, Changsha 410081, China.
| | - Yize Sun
- College of Environmental Science and Engineering, Hunan University, Changsha 410082, China
| | - Fengwei Ran
- College of Geographic Sciences, Hunan Normal University, Changsha 410081, China
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Cloyed CS, Wilson RM, Balmer BC, Hohn AA, Schwacke LH, Zolman ES, Tumlin MC, Wells RS, Barleycorn AA, Allen JB, Carmichael RH. Specialization of a mobile, apex predator affects trophic coupling among adjacent habitats. Sci Rep 2021; 11:19611. [PMID: 34608172 PMCID: PMC8490471 DOI: 10.1038/s41598-021-99017-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2020] [Accepted: 09/13/2021] [Indexed: 11/23/2022] Open
Abstract
Mobile, apex predators are commonly assumed to stabilize food webs through trophic coupling across spatially distinct habitats. The assumption that trophic coupling is common remains largely untested, despite evidence that individual behaviors might limit trophic coupling. We used stable isotope data from common bottlenose dolphins across the Gulf of Mexico to determine if these apex predators coupled estuarine and adjacent, nearshore marine habitats. δ13C values differed among the sites, likely driven by environmental factors that varied at each site, such as freshwater input and seagrass cover. Within most sites, δ13C values differed such that dolphins sampled in the upper reaches of embayments had values indicative of estuarine habitats while those sampled outside or in lower reaches of embayments had values indicative of marine habitats. δ15N values were more similar among and within sites than δ13C values. Data from multiple tissues within individuals corroborated that most dolphins consistently used a narrow range of habitats but fed at similar trophic levels in estuarine and marine habitats. Because these dolphins exhibited individual habitat specialization, they likely do not contribute to trophic coupling between estuarine and adjacent marine habitats at a regional scale, suggesting that not all mobile, apex predators trophically couple adjacent habitats.
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Affiliation(s)
- Carl S Cloyed
- Dauphin Island Sea Lab, Dauphin Island, AL, 36528, USA. .,Department of Marine Sciences, University of South Alabama, Mobile, AL, 36688, USA.
| | - Rachel M Wilson
- Department of Earth, Ocean, and Atmospheric Science, Florida State University, Tallahassee, FL, 32306, USA
| | - Brian C Balmer
- National Marine Mammal Foundation, San Diego, CA, 92106, USA
| | - Aleta A Hohn
- NOAA, National Marine Fisheries Service, Southeast Fisheries Science Center, Beaufort, NC, 28516, USA
| | - Lori H Schwacke
- National Marine Mammal Foundation, San Diego, CA, 92106, USA
| | - Eric S Zolman
- National Marine Mammal Foundation, San Diego, CA, 92106, USA
| | - Mandy C Tumlin
- Louisiana Department of Wildlife and Fisheries, Baton Rouge, LA, 70808, USA
| | - Randall S Wells
- Chicago Zoological Society's Sarasota Dolphin Research Program, c/o Mote Marine Laboratory, Sarasota, FL, 34236, USA
| | - Aaron A Barleycorn
- Chicago Zoological Society's Sarasota Dolphin Research Program, c/o Mote Marine Laboratory, Sarasota, FL, 34236, USA
| | - Jason B Allen
- Chicago Zoological Society's Sarasota Dolphin Research Program, c/o Mote Marine Laboratory, Sarasota, FL, 34236, USA
| | - Ruth H Carmichael
- Dauphin Island Sea Lab, Dauphin Island, AL, 36528, USA.,Department of Marine Sciences, University of South Alabama, Mobile, AL, 36688, USA
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Cloyed CS, Balmer BC, Schwacke LH, Wells RS, Berens McCabe EJ, Barleycorn AA, Allen JB, Rowles TK, Smith CR, Takeshita R, Townsend FI, Tumlin MC, Zolman ES, Carmichael RH. Interaction between dietary and habitat niche breadth influences cetacean vulnerability to environmental disturbance. Ecosphere 2021. [DOI: 10.1002/ecs2.3759] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
Affiliation(s)
- Carl S. Cloyed
- Dauphin Island Sea Lab 101 Bienville Boulevard Dauphin Island Alabama 36608 USA
- Department of Marine Sciences University of South Alabama Mobile Alabama 36688 USA
| | - Brian C. Balmer
- National Marine Mammal Foundation 3419 Maybank Highway Johns Island South Carolina 29487 USA
| | - Lori H. Schwacke
- National Marine Mammal Foundation 3419 Maybank Highway Johns Island South Carolina 29487 USA
| | - Randall S. Wells
- Chicago Zoological Society’s Sarasota Dolphin Research Program, c/o Mote Marine Laboratory 1600 Ken Thompson Parkway Sarasota Florida 34236 USA
| | - Elizabeth J. Berens McCabe
- Chicago Zoological Society’s Sarasota Dolphin Research Program, c/o Mote Marine Laboratory 1600 Ken Thompson Parkway Sarasota Florida 34236 USA
| | - Aaron A. Barleycorn
- Chicago Zoological Society’s Sarasota Dolphin Research Program, c/o Mote Marine Laboratory 1600 Ken Thompson Parkway Sarasota Florida 34236 USA
| | - Jason B. Allen
- Chicago Zoological Society’s Sarasota Dolphin Research Program, c/o Mote Marine Laboratory 1600 Ken Thompson Parkway Sarasota Florida 34236 USA
| | - Teresa K. Rowles
- Office of Protected Resources National Marine Fisheries Service NOAA 1315 East West Highway Silver Spring Maryland 20910 USA
| | - Cynthia R. Smith
- National Marine Mammal Foundation 2240 Shelter Island Drive #200 San Diego California 92106 USA
| | - Ryan Takeshita
- National Marine Mammal Foundation 3419 Maybank Highway Johns Island South Carolina 29487 USA
| | - Forrest I. Townsend
- Bayside Hospital for Animals 251 Racetrack Road NE Fort Walton Beach Florida 32547 USA
| | - Mandy C. Tumlin
- Louisiana Department of Wildlife and Fisheries 2000 Quail Drive Baton Rouge Louisiana 70808 USA
| | - Eric S. Zolman
- National Marine Mammal Foundation 3419 Maybank Highway Johns Island South Carolina 29487 USA
| | - Ruth H. Carmichael
- Dauphin Island Sea Lab 101 Bienville Boulevard Dauphin Island Alabama 36608 USA
- Department of Marine Sciences University of South Alabama Mobile Alabama 36688 USA
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Cloyed CS, Balmer BC, Schwacke LH, Takeshita R, Hohn A, Wells RS, Rowles TK, Saliki JT, Smith CR, Tumlin MC, Zolman ES, Fauquier DA, Carmichael RH. Linking morbillivirus exposure to individual habitat use of common bottlenose dolphins (Tursiops truncatus) between geographically different sites. J Anim Ecol 2021; 90:1191-1204. [PMID: 33608907 DOI: 10.1111/1365-2656.13446] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2020] [Accepted: 01/16/2021] [Indexed: 11/30/2022]
Abstract
Dolphin morbillivirus (DMV) is a virulent pathogen that causes high mortality outbreaks in delphinids globally and is spread via contact among individuals. Broadly ranging nearshore and open-ocean delphinids are likely reservoir populations that transmit DMV to estuarine populations. We assessed the seroprevalence of DMV antibodies and determined the habitat use of common bottlenose dolphins, Tursiops truncatus truncatus, from two estuarine sites, Barataria Bay and Mississippi Sound, in the northern Gulf of Mexico. We predicted that risk to DMV exposure in estuarine dolphins is driven by spatial overlap in habitat use with reservoir populations. Serum was collected from live-captured dolphins and tested for DMV antibodies. Habitat use of sampled individuals was determined by analysing satellite-tracked movements and stable isotope values. DMV seroprevalences were high among dolphins at Barataria Bay (37%) and Mississippi Sound (44%), but varied differently within sites. Ranging patterns of Barataria Bay dolphins were categorized into two groups: Interior and Island-associated. DMV seroprevalences were absent in Interior dolphins (0%) but high in Island-associated dolphins (45%). Ranging patterns of Mississippi Sound dolphins were categorized into three groups: Interior, Island-east and Island-west. DMV seroprevalences were detected across Mississippi Sound (Interior: 60%; Island-east: 20%; and Island-west: 43%). At both sites, dolphins in habitats with greater marine influence had enriched δ13 C values, and Barataria Bay dolphins with positive DMV titres had carbon isotope values indicative of marine habitats. Positive titres for DMV antibodies were more common in the lower versus upper parts of Barataria Bay but evenly distributed across Mississippi Sound. A dolphin's risk of exposure to DMV is influenced by how individual ranging patterns interact with environmental geography. Barataria Bay's partially enclosed geography likely limits the nearshore or open-ocean delphinids that carry DMV from interacting with dolphins that use interior, estuarine habitats, decreasing their exposure to DMV. Mississippi Sound's relatively open geography allows for greater spatial overlap and mixing among estuarine, nearshore and/or open-ocean cetaceans. The spread of DMV, and likely other diseases, is affected by the combination of individual movements, habitat use and the environment.
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Affiliation(s)
- Carl S Cloyed
- Dauphin Island Sea Lab, Dauphin Island, AL, USA.,Department of Marine Sciences, University of South Alabama, Mobile, AL, USA
| | | | | | | | - Aleta Hohn
- NOAA, National Marine Fisheries Service, Southeast Fisheries Science Center, Beaufort, NC, USA
| | - Randall S Wells
- Chicago Zoological Society's Sarasota Dolphin Research Program, c/o Mote Marine Laboratory, Sarasota, FL, USA
| | - Teresa K Rowles
- NOAA, National Marine Fisheries Service, Office of Protected Resources, Silver Spring, MD, USA
| | - Jeremiah T Saliki
- Athens Veterinary Diagnostic Laboratory, University of Georgia, Athens, GA, USA
| | | | - Mandy C Tumlin
- Louisiana Department of Wildlife and Fisheries, Baton Rouge, LA, USA
| | - Eric S Zolman
- National Marine Mammal Foundation, San Diego, CA, USA
| | - Deborah A Fauquier
- NOAA, National Marine Fisheries Service, Office of Protected Resources, Silver Spring, MD, USA
| | - Ruth H Carmichael
- Dauphin Island Sea Lab, Dauphin Island, AL, USA.,Department of Marine Sciences, University of South Alabama, Mobile, AL, USA
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10
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Smith KJ, Trueman CN, France CAM, Peterson MJ. Evaluation of two lipid removal methods for stable carbon and nitrogen isotope analysis in whale tissue. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2020; 34:e8851. [PMID: 32492222 DOI: 10.1002/rcm.8851] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/20/2020] [Revised: 04/30/2020] [Accepted: 06/02/2020] [Indexed: 06/11/2023]
Abstract
RATIONALE The presence of lipids in animal tissues can influence the interpretation of stable isotope data, particularly in lipid-rich tissues such as the skin and muscle of marine mammals. The traditionally employed chloroform-methanol delipidation protocol has the potential to alter δ15 N values in proteinaceous tissues. Our objective was to determine whether the use of cyclohexane could be an alternative extraction method, effectively removing lipids without altering δ15 N values. METHODS Kidney, liver, muscle, and skin samples were collected from beach-cast Sowerby's beaked whales (Mesoplodon bidens). Control subsamples were processed without delipidation extraction, and duplicate subsamples were extracted with either chloroform-methanol or cyclohexane. δ13 C, δ15 N, and C:N values were determined by continuous-flow elemental analysis isotope ratio mass spectrometry. Paired Wilcoxon tests were used to evaluate the change in isotope ratios after extraction, and unpaired Wilcoxon tests were used to evaluate differences in isotope ratios between extractions. RESULTS Use of cyclohexane is an effective delipidation technique for tissues with low and moderate lipid content. Chemical delipidation influenced δ15 N values; extracted samples generally showed an increase in δ15 N values which varied from 0.0‰ to 1.7‰. Chloroform-methanol extraction resulted in alterations to δ15 N values greater than the analytical precision for all analyzed tissues. Changes to δ15 N values after cyclohexane extraction were at or near the analytical precision for liver and muscle but greater than the analytical precision for kidney and skin. CONCLUSIONS We recommend processing duplicate subsamples for stable isotope analysis, one with and one without extraction, in order to obtain accurate values for each isotope ratio. Prolonged chemical extractions are not necessary to effectively remove lipids. When samples are limited, we suggest using cyclohexane for tissues with low or moderate lipid content, and chloroform-methanol for lipid-rich tissues.
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Affiliation(s)
- Kerri J Smith
- Department of Biological Sciences, University of Texas at El Paso, El Paso, Texas, USA
- Department of Vertebrate Zoology, National Museum of Natural History, Washington, DC, USA
| | - Clive N Trueman
- Ocean and Earth Science, University of Southampton, National Oceanography Centre, Southampton, SO45 4PJ, UK
| | - Christine A M France
- Museum Conservation Institute, Smithsonian Institution, Suitland, MD, 20746, USA
| | - Markus J Peterson
- Department of Biological Sciences, University of Texas at El Paso, El Paso, Texas, USA
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