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Gerber R, de Necker L, van Vuren JHJ, Ikenaka Y, Nakayama SMM, Ishizuka M, Wepener V, Smit NJ. A stable isotope analysis of the dietary patterns of the aquatic apex predator, the African tigerfish (Hydrocynus vittatus). JOURNAL OF FISH BIOLOGY 2023; 103:1129-1143. [PMID: 37498144 DOI: 10.1111/jfb.15516] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/26/2023] [Revised: 07/19/2023] [Accepted: 07/26/2023] [Indexed: 07/28/2023]
Abstract
Stable isotope analyses, specifically δ13 C and δ15 N, are useful tools increasingly used to understand ecosystem function, food web structures, and consumer diets. Although the iconic tigerfish Hydrocynus vittatus is regarded as an apex predator in southern African freshwater systems, little information is available regarding their feeding behavior and how this may change with growth or differ between ecosystems, with most information stemming from stomach content analyses (SCA). The aim of the present study was to address this lack of information through a baseline study of the diet of large and small tigerfish in various lentic and lotic ecosystems in South Africa using stable isotope methods. Fish and various food web components and food sources were collected from two river and two lake ecosystems in South Africa. The δ13 C and δ15 N values for all samples were determined and multivariate analyses and Bayesian analytical techniques applied to determine the feeding ecology of H. vittatus and how this may differ with size and habitat type. Analyses revealed a substantial difference in the type and abundance of food sources contributing to the diet of H. vittatus between ecosystems, most prominently between the lotic systems, where less dietary specialization was observed, and lentic systems where more specialization was observed. Furthermore, there was a distinct difference in diet between small and large tigerfish, especially in the lotic system, indicating an ontogenetic diet shift as tigerfish grow and further supporting previous SCA studies. This is the first study of its kind on the African continent for H. vittatus and the findings illustrate the value of stable isotope analysis in providing in-depth information into the feeding ecology of consumers and how this may differ between size classes and habitat types.
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Grants
- 127549 Department of Science and Innovation Professional Development Programme
- 22KK0163 Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan
- 17KK0009 Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan
- 18KK028708 Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan
- 17K2003807 Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan
- 18H0413208 Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan
- 20K20633 Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan
- 105979 National Research Foundation of South Africa
- 85505 National Research Foundation of South Africa
- 105122 National Research Foundation of South Africa
- K5-1922 Water Research Commission of South Africa
- K5-2185 Water Research Commission of South Africa
- JPMJSA1501 JST/JICA SATREPS (Science and Technology Research Partnership for Sustainable Development
- JPMJAS2001 aXis (Accelerating Social Implementation for SDGs Achievement
- PJ36210002 JST AJ-CORE
- JSPS CORE to CORE program
- Hokkaido University SOUSEI Tokutei Research
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Affiliation(s)
- Ruan Gerber
- Water Research Group, Unit for Environmental Sciences and Management, North-West University, Potchefstroom, South Africa
| | - Lizaan de Necker
- Water Research Group, Unit for Environmental Sciences and Management, North-West University, Potchefstroom, South Africa
- South African Institute for Aquatic Biodiversity (NRF-SAIAB), Makhanda, South Africa
| | - Johan H J van Vuren
- Water Research Group, Unit for Environmental Sciences and Management, North-West University, Potchefstroom, South Africa
| | - Yoshinori Ikenaka
- Water Research Group, Unit for Environmental Sciences and Management, North-West University, Potchefstroom, South Africa
- Laboratory of Toxicology, Department of Environmental Veterinary Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo, Japan
- Translational Research Unit, Veterinary Teaching hospital, Faculty of Veterinary Medicine, Hokkaido University, Sapporo, Japan
- One Health Research Center, Hokkaido University, Sapporo, Japan
| | - Shouta M M Nakayama
- Laboratory of Toxicology, Department of Environmental Veterinary Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo, Japan
| | - Mayumi Ishizuka
- Laboratory of Toxicology, Department of Environmental Veterinary Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo, Japan
| | - Victor Wepener
- Water Research Group, Unit for Environmental Sciences and Management, North-West University, Potchefstroom, South Africa
| | - Nico J Smit
- Water Research Group, Unit for Environmental Sciences and Management, North-West University, Potchefstroom, South Africa
- South African Institute for Aquatic Biodiversity (NRF-SAIAB), Makhanda, South Africa
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de Necker L, Brendonck L, Gerber R, Lemmens P, Soto DX, Ikenaka Y, Ishizuka M, Wepener V, Smit NJ. Drought altered trophic dynamics of an important natural saline lake: A stable isotope approach. THE SCIENCE OF THE TOTAL ENVIRONMENT 2022; 834:155338. [PMID: 35452726 DOI: 10.1016/j.scitotenv.2022.155338] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/18/2022] [Revised: 04/07/2022] [Accepted: 04/13/2022] [Indexed: 06/14/2023]
Abstract
Climate change and associated droughts threaten the ecology and resilience of natural saline lakes globally. There is a distinct lack of research regarding their ecological response to climatic events in the Global South. This region is predicted to experience climatic events such as El Niño-Southern Oscillation (ENSO) more often and with greater severity with the potential to alter the structure and functioning of aquatic ecosystems significantly. From 2015 to 2016 South Africa experienced one of the most severe country-wide droughts as a result of a strong ENSO event. Our study aimed to investigate the effect of this supra-seasonal drought on the trophic structure of fish communities in a naturally saline shallow lake of a Ramsar wetland using stable isotope techniques. Fishes and potential basal sources were collected from the lake, during predrought conditions in 2010 and after severe drought (recovery phase; 2017). The δ13C and δ15N values of food web elements were determined and analysed using Bayesian mixing models and Bayesian Laymen metrics to establish the proportional contribution of C3 and C4 basal sources to the fish (consumer) diets, and examine the fish community in terms of isotopic niche and trophic structure, respectively. Fish consumers relied predominantly on C3 basal sources in the predrought and shifted to greater reliance on C4 basal sources, decreased isotopic niche space use and a reduction in trophic length in the recovery phase. Drought altered the type and abundance of the basal sources available by limiting sources to those that are more drought-tolerant, reducing the trophic pathways of the food web with no significant alterations in the fish community. These results demonstrate the resilience and biological plasticity of Lake Nyamithi and its aquatic fauna, highlighting the importance of freshwater inflow to saline lakes with alterations thereof posing a significant threat to their continued functioning.
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Affiliation(s)
- Lizaan de Necker
- Water Research Group, Unit for Environmental Sciences and Management, North-West University, Private Bag X6001, Potchefstroom 2520, South Africa; South African Institute for Aquatic Biodiversity (NRF-SAIAB), Makhanda 6139, South Africa.
| | - Luc Brendonck
- Water Research Group, Unit for Environmental Sciences and Management, North-West University, Private Bag X6001, Potchefstroom 2520, South Africa; Animal Ecology, Global Change and Sustainable Development, Department of Biology, University of Leuven, 32 Charles Deberiotstraat, Leuven 3000, Belgium.
| | - Ruan Gerber
- Water Research Group, Unit for Environmental Sciences and Management, North-West University, Private Bag X6001, Potchefstroom 2520, South Africa
| | - Pieter Lemmens
- Laboratory of Aquatic Ecology, Evolution and Conservation, KU Leuven, Ch. Deberiotstraat 32, 3000 Leuven, Belgium; Leibniz Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 310, 12587 Berlin, Germany.
| | - David X Soto
- Department of Nuclear Sciences and Applications, Division of Physical and Chemical Sciences, Isotope Hydrology Section, International Atomic Energy Agency, Vienna, Austria.
| | - Yoshinori Ikenaka
- Water Research Group, Unit for Environmental Sciences and Management, North-West University, Private Bag X6001, Potchefstroom 2520, South Africa; Laboratory of Toxicology, Department of Environmental Veterinary Sciences, Faculty of Veterinary Medicine, Hokkaido University, Kita 18, Nishi 9, Kita-ku, Sapporo 060-0818, Japan; Translational Research Unit, Veterinary Teaching Hospital, Faculty of Veterinary Medicine, Hokkaido University, Kita 18, Nishi 9, Kita-ku, Sapporo 060-0818, Japan; One Health Research Center, Hokkaido University, Kita 18, Nishi 9, Kita-ku, Sapporo 060-0818, Japan.
| | - Mayumi Ishizuka
- Laboratory of Toxicology, Department of Environmental Veterinary Sciences, Faculty of Veterinary Medicine, Hokkaido University, Kita 18, Nishi 9, Kita-ku, Sapporo 060-0818, Japan.
| | - Victor Wepener
- Water Research Group, Unit for Environmental Sciences and Management, North-West University, Private Bag X6001, Potchefstroom 2520, South Africa.
| | - Nico J Smit
- Water Research Group, Unit for Environmental Sciences and Management, North-West University, Private Bag X6001, Potchefstroom 2520, South Africa.
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Woodborne S, Botha H, Huchzermeyer D, Myburgh J, Hall G, Myburgh A. Ontogenetic dependence of Nile crocodile (Crocodylus niloticus) isotope diet-to-tissue discrimination factors. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2021; 35:e9159. [PMID: 34224610 DOI: 10.1002/rcm.9159] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/20/2021] [Revised: 06/25/2021] [Accepted: 06/27/2021] [Indexed: 06/13/2023]
Abstract
RATIONALE The diet of wild Nile crocodiles (Crocodylus niloticus) is difficult to assess because they are cryptic and nocturnal predators that are extremely sensitive to disturbance by observers, and stomach content analysis is challenging, especially in large specimens. Stable light isotope analysis provides a means of assessing their diet, but diet-to-tissue discrimination factors have yet to be established for the species. METHODS Isotope ratio (15 N/14 N and 13 C/12 C expressed as δ15 N and δ13 C) analyses of scutes, claws, and blood of farmed crocodiles of different sizes were compared with the isotope values of their lifelong diet, which comprises chickens from a single supplier. RESULTS Systematic size dependence in the diet-to-tissue discrimination factors for scute collagen, scute keratin, and claw keratin is described in regression relationships against the snout to vent length. Fixed values are presented for erythrocytes and blood plasma because blood was not sampled from juveniles. CONCLUSIONS The diet-to-tissue discrimination factors help assess the diet of wild crocodiles. The diet of crocodiles from Lake Flag Boshielo shows a clear ontogenic shift, as has been seen in other studies, and the results strongly indicate a dependence on the terrestrial food web rather than a fish diet. That this population may exploit a terrestrial diet highlights potential conflicts for conserving Nile crocodiles outside protected areas.
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Affiliation(s)
- Stephan Woodborne
- Tandem & AMS Laboratory, iThemba LABS, Johannesburg, South Africa
- Stable Isotope Laboratory, Mammal Research Institute, University of Pretoria, Pretoria, South Africa
| | - Hannes Botha
- Mpumalanga Tourism and Parks Agency, Scientific Services, Nelspruit, South Africa
- Department of Biodiversity, University of Limpopo, Sovenga, South Africa
| | | | - Jan Myburgh
- Department of Paraclinical Sciences, Faculty of Veterinary Science, University of Pretoria, Onderstepoort, South Africa
| | - Grant Hall
- Stable Isotope Laboratory, Mammal Research Institute, University of Pretoria, Pretoria, South Africa
| | - Albert Myburgh
- Department of Zoology and Entomology, University of Pretoria, Pretoria, South Africa
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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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de Necker L, Manfrin A, Ikenaka Y, Ishizuka M, Brendonck L, van Vuren JHJ, Sures B, Wepener V, Smit NJ. Using stable δ13C and δ15N isotopes to assess foodweb structures in an African subtropical temporary pool. AFRICAN ZOOLOGY 2020. [DOI: 10.1080/15627020.2020.1731331] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Affiliation(s)
- L de Necker
- Water Research Group, Unit for Environmental Sciences and Management, North-West University, Potchefstroom, South Africa
| | - A Manfrin
- Environmental Campus Birkenfeld, University of Applied Sciences Tier, Standort Umwelt-Campus Birkenfeld, Germany
- Department of Aquatic Ecology and Centre for Water and Environmental Research (ZWU), University of Duisburg-Essen, Essen, Germany
| | - Y Ikenaka
- Water Research Group, Unit for Environmental Sciences and Management, North-West University, Potchefstroom, South Africa
- Laboratory of Toxicology, Department of Environmental Veterinary Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo, Japan
| | - M Ishizuka
- Laboratory of Toxicology, Department of Environmental Veterinary Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo, Japan
| | - L Brendonck
- Water Research Group, Unit for Environmental Sciences and Management, North-West University, Potchefstroom, South Africa
- Animal Ecology, Global Change and Sustainable Development, Department of Biology, University of Leuven, Leuven, Belgium
| | - JHJ van Vuren
- Water Research Group, Unit for Environmental Sciences and Management, North-West University, Potchefstroom, South Africa
| | - B Sures
- Department of Aquatic Ecology and Centre for Water and Environmental Research (ZWU), University of Duisburg-Essen, Essen, Germany
| | - V Wepener
- Water Research Group, Unit for Environmental Sciences and Management, North-West University, Potchefstroom, South Africa
| | - NJ Smit
- Water Research Group, Unit for Environmental Sciences and Management, North-West University, Potchefstroom, South Africa
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