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Petrov K, Van Dyke JU, Georges A, Keitel C, Spencer RJ. Maternal diet influences fecundity in a freshwater turtle undergoing population decline. CONSERVATION PHYSIOLOGY 2024; 12:coae033. [PMID: 38803426 PMCID: PMC11129712 DOI: 10.1093/conphys/coae033] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/01/2023] [Revised: 03/20/2024] [Accepted: 05/03/2024] [Indexed: 05/29/2024]
Abstract
Food availability determines the amount of energy animals can acquire and allocate to reproduction and other necessary functions. Female animals that are food limited thus experience reduced energy available for reproduction. When this occurs, females may reduce frequency of reproductive events or the number or size of offspring per reproductive bout. We assessed how maternal diet affects reproductive output in adult female Murray River short-necked turtles, Emydura macquarii, from four wetlands in Victoria. We previously found that turtle diets differ in the composition of plants and animals between our study wetlands. In this study, we tested whether differences in turtle diet composition (i.e. plants and animals) at these wetlands were associated with differences in clutch mass, individual egg mass, bulk egg composition and hatching success. We found total clutch mass increased with maternal body size at each site. At sites where filamentous green algae were scarce and E. macquarii were carnivorous, females produced smaller clutches relative to body size compared to females from sites where algae were abundant, and turtles were more herbivorous. Individual egg mass, bulk egg composition and hatching success did not differ across wetlands. Isotopic analysis revealed significant positive relationships between the carbon and nitrogen isotopes (δ13C, δ15N) of the eggs and those of the mothers, indicating that mothers allocated ratios of carbon and nitrogen isotopes to their eggs similar to those present in their tissues. Our study suggests that at sites where females are more carnivorous due to a relative absence of algae, females produce smaller clutches, but other aspects of their reproduction are not significantly impacted. The reduction in clutch size associated with differences in the availability of dietary plants and animals may have long-term consequences for E. macquarii and other freshwater turtle species that are experiencing population declines.
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Affiliation(s)
- Kristen Petrov
- School of Science, Hawkesbury Institute, Western Sydney University Locked Bag, 1797, Penrith South DC, NSW 2751, Australia
| | - James U Van Dyke
- Centre for Freshwater Ecosystems, Department of Environment and Genetics, School of Agriculture, Biomedical and Environment, La Trobe University, Albury-Wodonga Campus, PO Box 821, Wodonga, VIC 3689, Australia
| | - Arthur Georges
- Institute for Applied Ecology, University of Canberra, 11 Kirinari Street,Bruce, ACT 2601, Australia
| | - Claudia Keitel
- School of Life and Environmental Sciences, University of Sydney, 380 Werombi Road, Brownlow Hill, NSW 2570, Australia
| | - Ricky-John Spencer
- School of Science, Hawkesbury Institute, Western Sydney University Locked Bag, 1797, Penrith South DC, NSW 2751, Australia
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Ecological Traits and Trophic Plasticity in The Greater Pipefish Syngnathus acus in the NW Iberian Peninsula. BIOLOGY 2022; 11:biology11050712. [PMID: 35625444 PMCID: PMC9138823 DOI: 10.3390/biology11050712] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/07/2022] [Revised: 04/25/2022] [Accepted: 05/02/2022] [Indexed: 11/16/2022]
Abstract
The great pipefish Syngnathus acus is one of the most representative European syngnathids, being highly associated with seagrass and macroalgal beds. Surprisingly, the ecology of this large ovoviviparous marine fish has received scanty attention. The population inhabiting three sites on Cíes Archipelago (Atlantic Islands National Park, NW Spain) was monitored in 2017–2018 for spatial and temporal changes in abundances, reproduction traits, trophic niche occupancy, and dietary regimes across reproduction states, through an isotopic (δ13C and δ15N) approach. Abundances were highly variable across seasons and sites, decreasing significantly from mid-autumn. The population consisted almost exclusively of large adults that migrate by the end of the breeding season, which extended from mid-spring to summer. Operational sex ratios suggest that the species is sex-role reversed. S. acus is a secondary consumer (Trophic position = 3.36 ± 0.05), preferring amphipods but displaying annual and seasonal dietary plasticity. Mature fish were less selective than immatures (especially females), with a higher preference for amphipods (36–68%) in the former. The second most-preferred prey were carideans, copepods, or isopods, depending on the year and the reproduction state. Overall, the wider trophic niches in females and immature specimens compared to males and mature fish would indicate a higher variability in both the use of prey resources and/or their origin. The present study highlights the trophic plasticity and unique features of S. acus population in the Cíes Archipelago, especially regarding the outstanding size of the fish and the exceptional occurrence of breeders.
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Cutting KA, Rotella JJ, Grusing E, Waxe JA, Nunlist E, Sowell BF. Nutrient sources for offspring formation: diet-mother and mother-offspring isotope discrimination in domesticated gallinaceous birds. ISOTOPES IN ENVIRONMENTAL AND HEALTH STUDIES 2021; 57:553-562. [PMID: 34632885 DOI: 10.1080/10256016.2021.1984905] [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: 12/16/2020] [Accepted: 08/26/2021] [Indexed: 06/13/2023]
Abstract
Stable isotope techniques can be used to assess nutrient acquisition and allocation strategies used to produce offspring. Before stable isotope techniques can be employed, researchers need reliable isotope discrimination values. In this context, isotope discrimination compares the difference in the isotope ratio between the maternal-offspring tissue that occurs during nutrient transfer prior to egg laying. Currently, isotope discrimination values are unknown between the maternal blood constituents - that reflect different temporal scales of integration - and downy feathers of their offspring. In this study, we experimentally derive isotope discrimination relationships between maternal diet-blood constituents for egg laying, and between maternal blood constituents-down feathers of offspring in an experiment with 3 types of domesticated gallinaceous birds raised on known diets. Our experiment is the first to report isotope discrimination values for maternal blood constituents-down of offspring in avian taxa and provides a new sampling technique that is less invasive than previously available as collecting down does not require sampling viable eggs or individuals. Future researchers can use these results to assist in identifying nutrient sources used by adult birds to produce young.
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Affiliation(s)
- Kyle A Cutting
- Red Rock Lakes National Wildlife Refuge, U.S. Fish and Wildlife Service, Lima, MT, USA
- Department of Ecology, Montana State University, Bozeman, MT, USA
| | - Jay J Rotella
- Department of Ecology, Montana State University, Bozeman, MT, USA
| | - Emma Grusing
- Red Rock Lakes National Wildlife Refuge, U.S. Fish and Wildlife Service, Lima, MT, USA
| | - James A Waxe
- The Centennial Sandhills Preserve, The Nature Conservancy, Lima, MT, USA
| | - Erika Nunlist
- Department of Animal and Range Sciences, Montana State University, Bozeman, MT, USA
| | - Bok F Sowell
- Department of Animal and Range Sciences, Montana State University, Bozeman, MT, USA
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Baró-Camarasa I, Marmolejo-Rodríguez AJ, O'Hara TM, Elorriaga-Verplancken FR, Trejo-Ramírez A, Martínez-Rincón RO, Galván-Magaña F. Isotopic (δ 15 N) relationship of pregnant females and their embryos: Comparing placental and yolk-sac viviparous elasmobranchs. JOURNAL OF FISH BIOLOGY 2021; 98:784-790. [PMID: 33230841 DOI: 10.1111/jfb.14625] [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: 09/03/2020] [Revised: 11/11/2020] [Accepted: 11/21/2020] [Indexed: 06/11/2023]
Abstract
Nitrogen stable isotopes ratios (δ15 N) were determined for selected tissues (muscle, liver, blood and yolk) of pregnant females and their embryos of a placental viviparous species, the Pacific sharpnose shark (Rhizoprionodon longurio), and a yolk-sac viviparous species, the speckled guitarfish (Pseudobatos glaucostigmus). The R. longurio embryo tissues were 15 N enriched compared to the same tissues in the pregnant female, using the difference in δ15 N (Δδ15 N) between embryo and adult. Mean Δδ15 N was 2.17‰ in muscle, 4.39‰ in liver and 0.80‰ in blood. For P. glaucostigmus, embryo liver tissue was significantly 15 N enriched in comparison with liver of the pregnant female (Δδ15 N mean = 1.22‰), whereas embryo muscle was 15 N depleted relative to the muscle of the pregnant female (Δδ15 N mean = -1.22‰). Both species presented a significant positive linear relationship between Δδ15 N and embryo total length (LT ). The results indicated that embryos have different Δδ15 N depending on their reproductive strategy, tissue type analysed and embryo LT .
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Affiliation(s)
- Isis Baró-Camarasa
- Instituto Politécnico Nacional, Centro Interdisciplinario de Ciencias Marinas, La Paz, Mexico
| | | | - Todd M O'Hara
- Bilingual Laboratory of Toxicology, Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, Texas, USA
| | | | | | | | - Felipe Galván-Magaña
- Instituto Politécnico Nacional, Centro Interdisciplinario de Ciencias Marinas, La Paz, Mexico
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Vanderklift MA, Pillans RD, Robson NA, Skrzypek G, Stubbs JL, Tucker AD. Comparisons of stable isotope composition among tissues of green turtles. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2020; 34:e8839. [PMID: 32436593 DOI: 10.1002/rcm.8839] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/10/2020] [Revised: 05/08/2020] [Accepted: 05/18/2020] [Indexed: 06/11/2023]
Abstract
UNLABELLED Ecologists often need to make choices about what body parts (tissues or organs) of an animal to sample. The decision is typically guided by the need to treat animals as humanely as possible, as well as the information that different body parts can provide. When using stable isotopes, decisions are also influenced by whether specimens would require preservation, and whether they have properties (such as high lipid concentrations) that would influence measurements. Sometimes we cannot use a preferred tissue (for example, because of ethical or logistical constraints), and in such cases an ability to reliably predict stable isotope composition for one tissue from data yielded by another would be useful. METHODS In this study we analysed multiple tissues (skin, whole blood, red blood cells, plasma and nail) from green turtles (Chelonia mydas) to evaluate variation in C:N ratios, and test hypotheses about the intercept and slope of regressions of stable carbon and nitrogen isotope compositions among tissues. RESULTS Regression models revealed that linear relationships were present for most comparisons, except those involving the δ13 C of skin, and the slopes (β1 ) of most regressions were different from unity. The C:N ratios of skin were significantly higher and more variable than those of other tissues. The δ13 C and δ15 N of nail were highly correlated with those of the whole blood, red blood cells and plasma. Nail and red blood cells showed low variation in C:N. CONCLUSIONS The patterns in slopes of regressions indicate that comparisons of measurements yielded by different tissues of wild animals are complicated by the fact that the tissues are unlikely to be in isotopic equilibrium with their diet. Of the tissues used in this study, nail is simple to collect, requires minimal disturbance to the animal and no special preservation; these traits should make it attractive to turtle ecologists, but more information is needed on aspects such as growth rates.
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Affiliation(s)
- Mathew A Vanderklift
- CSIRO Oceans & Atmosphere, Indian Ocean Marine Research Centre, Crawley, WA, 6009, Australia
| | - Richard D Pillans
- CSIRO Oceans & Atmosphere, Biosciences Precinct, St Lucia, Queensland, 4067, Australia
| | - Natalie A Robson
- CSIRO Oceans & Atmosphere, Indian Ocean Marine Research Centre, Crawley, WA, 6009, Australia
| | - Grzegorz Skrzypek
- School of Biological Sciences, The University of Western Australia, Crawley, WA, 6009, Australia
| | - Jessica L Stubbs
- CSIRO Oceans & Atmosphere, Indian Ocean Marine Research Centre, Crawley, WA, 6009, Australia
- School of Biological Sciences, The University of Western Australia, Crawley, WA, 6009, Australia
| | - Anton D Tucker
- Marine Science Program, Department of Biodiversity, Conservation and Attractions, Kensington, WA, 6151, Australia
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Studying animal niches using bulk stable isotope ratios: an updated synthesis. Oecologia 2020; 193:27-51. [DOI: 10.1007/s00442-020-04654-4] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2019] [Accepted: 04/11/2020] [Indexed: 10/24/2022]
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Chabot RM, Ceriani SA, Seminoff JA, Mills KA, Mansfield KL. Characterizing stable isotope relationships between green turtle (Chelonia mydas) skin and unhatched eggs. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2019; 33:1277-1285. [PMID: 31034695 DOI: 10.1002/rcm.8467] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/17/2018] [Revised: 02/28/2019] [Accepted: 04/15/2019] [Indexed: 06/09/2023]
Abstract
RATIONALE Stable isotope analysis is used to understand the foraging habits and movements of a diverse set of organisms. Variability in stable isotope ratios among tissues derived from the same animal makes it difficult to compare data among study results in which different tissue types are evaluated. Isotopic relationships between two green turtle (Chelonia mydas) tissue types, skin and unhatched egg contents are unknown. Similarly, few data exist to evaluate the influence of time elapsed after oviposition (as a proxy for decomposition) on isotopic variability among unhatched eggs within the same nest. METHODS Skin and unhatched egg contents were collected from 69 adult female green turtles and associated nests at the Archie Carr National Wildlife Refuge in Florida, USA. Values of δ13 C, δ15 N, and δ34 S were measured for both tissue types using a continuous flow isotope ratio mass spectrometer. Standardized major-axis (SMA) regression was used to generate conversion equations of carbon, nitrogen, and sulfur isotope ratios between the two tissue types. Model selection frameworks consisting of single-factor linear models were employed per isotope ratio to assess how egg time-in-nest affected intraclutch isotopic variability. RESULTS Conversion equations for all three isotope ratios indicated significant relationships between skin and unhatched egg values, although model fits were lower than found in some studies examining similar patterns in other marine turtle species. The probability of increased intraclutch variability was significantly higher among eggs collected at longer intervals after deposition. CONCLUSIONS This study reports the first-ever δ13 C and δ15 N conversion equations between skin and unhatched eggs for green turtles, and the first δ34 S conversion equation for any marine turtle species. SMA regression was used to directly convert tissue values bidirectionally, unlike equations generated using ordinary least-squares regression. Issues with increased intraclutch variability at later excavation dates highlight the importance of collecting unhatched eggs as soon as possible after hatchling emergence.
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Affiliation(s)
- Ryan M Chabot
- Marine Turtle Research Group, Department of Biological Sciences, University of Central Florida, Orlando, FL, USA
- Inwater Research Group, Inc., Jensen Beach, FL, USA
| | - Simona A Ceriani
- Marine Turtle Research Group, Department of Biological Sciences, University of Central Florida, Orlando, FL, USA
- Florida Fish and Wildlife Conservation Commission - Fish and Wildlife Research Institute, St. Petersburg, FL, USA
| | - Jeffrey A Seminoff
- National Oceanic and Atmospheric Administration - National Marine Fisheries Service, Southwest Fisheries Science Center, La Jolla, CA, USA
| | - Kali A Mills
- Marine Turtle Research Group, Department of Biological Sciences, University of Central Florida, Orlando, FL, USA
| | - Katherine L Mansfield
- Marine Turtle Research Group, Department of Biological Sciences, University of Central Florida, Orlando, FL, USA
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Turner Tomaszewicz CN, Seminoff JA, Price M, Kurle CM. Stable isotope discrimination factors and between-tissue isotope comparisons for bone and skin from captive and wild green sea turtles (Chelonia mydas). RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2017; 31:1903-1914. [PMID: 28857312 PMCID: PMC5653449 DOI: 10.1002/rcm.7974] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/16/2017] [Revised: 08/21/2017] [Accepted: 08/23/2017] [Indexed: 06/07/2023]
Abstract
RATIONALE The ecological application of stable isotope analysis (SIA) relies on taxa- and tissue-specific stable carbon (Δ13 C) and nitrogen (Δ15 N) isotope discrimination factors, determined with captive animals reared on known diets for sufficient time to reflect dietary isotope ratios. However, captive studies often prohibit lethal sampling, are difficult with endangered species, and reflect conditions not experienced in the wild. METHODS We overcame these constraints and determined the Δ13 C and Δ15 N values for skin and cortical bone from green sea turtles (Chelonia mydas) that died in captivity and evaluated the utility of a mathematical approach to predict discrimination factors. Using stable carbon (δ13 C values) and nitrogen (δ15 N values) isotope ratios from captive and wild turtles, we established relationships between bone stable isotope (SI) ratios and those from skin, a non-lethally sampled tissue, to facilitate comparisons of SI ratios among studies using multiple tissues. RESULTS The mean (±SD) Δ13 C and Δ15 N values (‰) between skin and bone from captive turtles and their diet (non-lipid-extracted) were 2.3 ± 0.3 and 4.1 ± 0.4 and 2.1 ± 0.6 and 5.1 ± 1.1, respectively. The mathematically predicted Δ13 C and Δ15 N values were similar (to within 1‰) to the experimentally derived values. The mean δ15 N values from bone were higher than those from skin for captive (+1.0 ± 0.9‰) and wild (+0.8 ± 1.0‰) turtles; the mean δ13 C values from bone were lower than those from skin for wild turtles (-0.6 ± 0.9‰), but the same as for captive turtles. We used linear regression equations to describe bone vs skin relationships and create bone-to-skin isotope conversion equations. CONCLUSIONS For sea turtles, we provide the first (a) bone-diet SI discrimination factors, (b) comparison of SI ratios from individual-specific bone and skin, and (c) evaluation of the application of a mathematical approach to predict stable isotope discrimination factors. Our approach opens the door for future studies comparing different tissues, and relating SI ratios of captive to wild animals.
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Affiliation(s)
- Calandra N. Turner Tomaszewicz
- Division of Biological Sciences, Ecology, Behavior, and Evolution Section, University of California, San Diego, La Jolla, California 92093-0116, USA
- Southwest Fisheries Science Center, NOAA, National Marine Fisheries Service, La Jolla, California 92037, USA
| | - Jeffrey A. Seminoff
- Southwest Fisheries Science Center, NOAA, National Marine Fisheries Service, La Jolla, California 92037, USA
| | - Mike Price
- SeaWorld San Diego, San Diego, California 92109, USA
| | - Carolyn M. Kurle
- Division of Biological Sciences, Ecology, Behavior, and Evolution Section, University of California, San Diego, La Jolla, California 92093-0116, USA
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Kaufman TJ, Pajuelo M, Bjorndal KA, Bolten AB, Pfaller JB, Williams KL, Vander Zanden HB. Mother-egg stable isotope conversions and effects of lipid extraction and ethanol preservation on loggerhead eggs. CONSERVATION PHYSIOLOGY 2014; 2:cou049. [PMID: 27293670 PMCID: PMC4806724 DOI: 10.1093/conphys/cou049] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/21/2014] [Revised: 09/22/2014] [Accepted: 09/23/2014] [Indexed: 06/06/2023]
Abstract
Carbon and nitrogen stable isotope (δ(13)C and δ(15)N) analysis has been used to elucidate foraging and migration behaviours of endangered sea turtle populations. Isotopic analysis of tissue samples from nesting females can provide information about their foraging locations before reproduction. To determine whether loggerhead (Caretta caretta) eggs provide a good proxy for maternal isotope values, we addressed the following three objectives: (i) we evaluated isotopic effects of ethanol preservation and lipid extraction on yolk; (ii) we examined the isotopic offset between maternal epidermis and corresponding egg yolk and albumen tissue δ(13)C and δ(15)N values; and (iii) we assessed the accuracy of foraging ground assignment using egg yolk and albumen stable isotope values as a proxy for maternal epidermis. Epidermis (n = 61), albumen (n = 61) and yolk samples (n = 24) were collected in 2011 from nesting females at Wassaw Island, GA, USA. Subsamples from frozen and ethanol-preserved yolk samples were lipid extracted. Both lipid extraction and ethanol preservation significantly affected yolk δ(13)C, while δ(15)N values were not altered at a biologically relevant level. The mathematical corrections provided here allow for normalization of yolk δ(13)C values with these treatments. Significant tissue conversion equations were found between δ(13)C and δ(15)N values of maternal epidermis and corresponding yolk and albumen. Finally, the consistency in assignment to a foraging area was high (up to 84%), indicating that these conversion equations can be used in future studies where stable isotopes are measured to determine female foraging behaviour and trophic relationships by assessing egg components. Loggerhead eggs can thus provide reliable isotopic information when samples from nesting females cannot be obtained.
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Affiliation(s)
- Temma J. Kaufman
- Archie Carr Center for Sea Turtle Research and Department of Biology, University of Florida, PO Box 118525, Gainesville, FL 32611, USA
| | - Mariela Pajuelo
- Archie Carr Center for Sea Turtle Research and Department of Biology, University of Florida, PO Box 118525, Gainesville, FL 32611, USA
| | - Karen A. Bjorndal
- Archie Carr Center for Sea Turtle Research and Department of Biology, University of Florida, PO Box 118525, Gainesville, FL 32611, USA
| | - Alan B. Bolten
- Archie Carr Center for Sea Turtle Research and Department of Biology, University of Florida, PO Box 118525, Gainesville, FL 32611, USA
| | - Joseph B. Pfaller
- Archie Carr Center for Sea Turtle Research and Department of Biology, University of Florida, PO Box 118525, Gainesville, FL 32611, USA
- Caretta Research Project, PO Box 9841, Savannah, GA 31412, USA
| | | | - Hannah B. Vander Zanden
- Archie Carr Center for Sea Turtle Research and Department of Biology, University of Florida, PO Box 118525, Gainesville, FL 32611, USA
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Vander Zanden HB, Tucker AD, Bolten AB, Reich KJ, Bjorndal KA. Stable isotopic comparison between loggerhead sea turtle tissues. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2014; 28:2059-2064. [PMID: 25156595 DOI: 10.1002/rcm.6995] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/15/2014] [Revised: 07/21/2014] [Accepted: 07/22/2014] [Indexed: 06/03/2023]
Abstract
RATIONALE Stable isotope analysis has been used extensively to provide ecological information about diet and foraging location of many species. The difference in isotopic composition between animal tissue and its diet, or the diet-tissue discrimination factor, varies with tissue type. Therefore, direct comparisons between isotopic values of tissues are inaccurate without an appropriate conversion factor. We focus on the loggerhead sea turtle (Caretta caretta), for which a variety of tissues have been used to examine diet, habitat use, and migratory origin through stable isotope analysis. We calculated tissue-to-tissue conversions between two commonly sampled tissues. METHODS Epidermis and scute (the keratin covering on the carapace) were sampled from 33 adult loggerheads nesting at two beaches in Florida (Casey Key and Canaveral National Seashore). Carbon and nitrogen stable isotope ratios were measured in the epidermis and the youngest portion of the scute tissue, which reflect the isotopic composition of the diet and habitat over similar time periods of the order of several months. RESULTS Significant linear relationships were observed between the δ(13)C and δ(15)N values of these two tissues, indicating they can be converted reliably. CONCLUSIONS Whereas both epidermis and scute samples are commonly sampled from nesting sea turtles to study trophic ecology and habitat use, the data from these studies have not been comparable without reliable tissue-to-tissue conversions. The equations provided here allow isotopic datasets using the two tissues to be combined in previously published and subsequent studies of sea turtle foraging ecology and migratory movement. In addition, we recommend that future isotopic comparisons between tissues of any organism utilize linear regressions to calculate tissue-to-tissue conversions.
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Affiliation(s)
- Hannah B Vander Zanden
- Archie Carr Center for Sea Turtle Research and Department of Biology, University of Florida, Gainesville, FL, 32611, USA; Department of Geology and Geophysics, University of Utah, Salt Lake City, UT, 84112, USA
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Marques TS, Lara NRF, Bassetti LAB, Piña CI, Camargo PB, Verdade LM. Intraspecific isotopic niche variation in broad-snouted caiman (Caiman latirostris). ISOTOPES IN ENVIRONMENTAL AND HEALTH STUDIES 2013; 49:325-335. [PMID: 24117429 DOI: 10.1080/10256016.2013.835309] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Strategies to minimise intraspecific competition are common in wild animals. For example, individuals may exploit food resources at different levels of the food chain. Analyses of stable isotopes are particularly useful for confirming variations in an intraspecific niche because the chemical composition of animals tends to reflect both the food consumed and the habitats occupied by the species. However, studies using this methodology to investigate neotropical crocodilians are scarce. This study aimed to verify the existence of ontogenetic and sexual niche variation in broad-snouted caiman in a silvicultural landscape in Brazil through the use of carbon and nitrogen stable isotopes. The isotopic ratios of carbon and nitrogen were determined in claw samples collected from 24 juveniles, 8 adults, and 16 hatchlings of C. latirostris. We identified a discrete ontogenetic variation in the isotopic niche and sexual difference only for juveniles. These results may indicate differences in the exploitation resources and a consequent reduction in competition between age classes.
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Affiliation(s)
- Thiago S Marques
- a Laboratório de Ecologia Isotópica, Centro de Energia Nuclear na Agricultura , Universidade de São Paulo , Piracicaba , Brazil
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