title: Diet-tissue stable isotope (Δ(13)C and Δ(15)N) discrimination factors for multiple tissues from terrestrial reptiles.
abstract: BACKGROUND
  Stable isotope analysis is a powerful tool for reconstructing trophic interactions to better understand drivers of community ecology. Taxon-specific stable isotope discrimination factors contribute to the best use of this tool. We determined the first Δ(13)C and Δ(15)N values for Rock Iguanas (Cyclura spp.) to better understand isotopic fractionation and estimate wild reptile foraging ecology.
  
  
  METHODS
  The Δ(13)C and Δ(15)N values between diet and skin, blood, and scat were determined from juvenile and adult iguanas held for 1 year on a known diet. We measured relationships between iguana discrimination factors and size/age and quantified effects of lipid extraction and acid treatment on stable isotope values from iguana tissues. Isotopic and elemental compositions were determined by Dumas combustion using an elemental analyzer coupled to an isotope ratio mass spectrometer using standards of known composition.
  
  
  RESULTS
  The Δ(13)C and Δ(15)N values ranged from -2.5 to +6.5‰ and +2.2 to +7.5‰, respectively, with some differences among tissues and between juveniles and adults. The Δ(13)C values from blood and skin differed among species, but not the Δ(15)N values. The Δ(13)C values from blood and skin and Δ(15)N values from blood were positively correlated with size/age. The Δ(13)C values from scat were negatively correlated with size (not age). Treatment with HCl (scat) and lipid extraction (skin) did not affect the isotope values.
  
  
  CONCLUSIONS
  These results should aid in the understanding of processes driving stable carbon and nitrogen isotope discrimination factors in reptiles. We provide estimates of Δ(13)C and Δ(15)N values and linear relationships between iguana size/age and discrimination factors for the best interpretation of wild reptile foraging ecology.
authors.affiliation: Division of Biological Sciences, Ecology, Behavior, and Evolution Section, University of California, San Diego, La Jolla, CA, 92093-0116, USA.
authors.forename: Ronnie
authors.initials: R
authors.lastname: Steinitz
authors.affiliation: San Diego Zoo Institute for Conservation Research, Behavioral Ecology Division, Escondido, CA, 92027-7000, USA.
authors.forename: Jeffrey M
authors.initials: JM
authors.lastname: Lemm
authors.affiliation: San Diego Zoo Institute for Conservation Research, Behavioral Ecology Division, Escondido, CA, 92027-7000, USA.
authors.forename: Stesha A
authors.initials: SA
authors.lastname: Pasachnik
authors.affiliation: Division of Biological Sciences, Ecology, Behavior, and Evolution Section, University of California, San Diego, La Jolla, CA, 92093-0116, USA.
authors.forename: Carolyn M
authors.initials: CM
authors.lastname: Kurle
mesh_terms: D000818:Animals; D002247:Carbon Isotopes / Q000032:analysis* / Q000378:metabolism; D004032:Diet; D013058:Mass Spectrometry; D009587:Nitrogen Isotopes / Q000032:analysis* / Q000378:metabolism; D012104:Reptiles; D014018:Tissue Distribution
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes