title: Diet-to-female and female-to-pup isotopic discrimination in South American sea lions.
abstract: BACKGROUND
  The use of accurate, species-specific diet-tissue discrimination factors is a critical requirement when applying stable isotope mixing models to predict consumer diet composition. Thus, diet-to-female and female-to-pup isotopic discrimination factors in several tissues for both captive and wild South American sea lions were estimated to provide appropriate values for quantifying feeding preferences at different timescales in the wild populations of this species.
  
  
  METHODS
  Stable carbon and nitrogen isotope ratios in the blood components of two female-pup pairs and females' prey muscle from captive individuals were determined by elemental analyzer/isotope ratio mass spectrometry (EA/IRMS) to calculate the respective isotopic discrimination factors. The same analysis was carried out in both blood components, and skin and hair tissues for eight female-pup pairs from wild individuals.
  
  
  RESULTS
  Mean diet-to-female Δ(13) C and Δ(15) N values were higher than the female-to-pup ones. Pup tissues were more (15) N-enriched than their mothers but (13) C-depleted in serum and plasma tissues. In most of the tissue comparisons, we found differences in both Δ(15) N and Δ(13) C values, supporting tissue-specific discrimination. We found no differences between captive and wild female-to-pup discrimination factors either in Δ(13) C or Δ(15) N values of blood components.
  
  
  CONCLUSIONS
  Only the stable isotope ratios in pup blood are good proxies of the individual lactating females. Thus, we suggest that blood components are more appropriate to quantify the feeding habits of wild individuals of this species. Furthermore, because female-to-pup discrimination factors for blood components did not differ between captive and wild individuals, we suggest that results for captive experiments can be extrapolated to wild South American sea lion populations.
authors.affiliation: Department of Ecology & Evolution, Centro Universitario Regional Este (CURE), University of the Republic (UdeLaR), C/Tacuarembó s/n, 20000, Maldonado, Uruguay.
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Drago
authors.affiliation: Department of Ecology & Evolution, Centro Universitario Regional Este (CURE), University of the Republic (UdeLaR), C/Tacuarembó s/n, 20000, Maldonado, Uruguay.|Proyecto Pinnípedos, Sección Etología, Facultad de Ciencias, Universidad de la República (UdeLaR), C/Iguá 4225, 11400, Montevideo, Uruguay.
authors.forename: Valentina
authors.initials: V
authors.lastname: Franco-Trecu
authors.affiliation: Department of Animal Biology and Biodiversity Research Institute (IRBio), University of Barcelona, Av. Diagonal 643, 08028, Barcelona, Spain.
authors.forename: Luis
authors.initials: L
authors.lastname: Cardona
authors.affiliation: Department of Ecology & Evolution, Centro Universitario Regional Este (CURE), University of the Republic (UdeLaR), C/Tacuarembó s/n, 20000, Maldonado, Uruguay.
authors.forename: Pablo
authors.initials: P
authors.lastname: Inchausti
mesh_terms: D000818:Animals; D000833:Animals, Suckling / Q000502:physiology*; D002247:Carbon Isotopes / Q000032:analysis* / Q000097:blood / Q000378:metabolism; D004032:Diet / Q000662:veterinary; D005247:Feeding Behavior / Q000502:physiology*; D005260:Female; D007774:Lactation; D009587:Nitrogen Isotopes / Q000032:analysis* / Q000097:blood / Q000378:metabolism; D046070:Sea Lions / Q000502:physiology*; D017747:Seafood / Q000032:analysis; D013020:South America; D014018:Tissue Distribution
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes