title: Should we use one-, or multi-compartment models to describe (13)C incorporation into animal tissues?
abstract: Understanding rates of isotopic incorporation and discrimination factors between tissues and diet is an important focus of ecologists seeking to use stable isotopes to track temporal changes in diet. We used a diet-shift experiment to measure differences among tissues in (13)C incorporation rates in house sparrows (Passer domesticus). We predicted faster incorporation rates in splanchnic than in structural tissues. We also assessed whether isotopic incorporation data were better supported by the one-compartment models most commonly used by ecologists or by multi-compartment models. We found large differences in the residence time of (13)C among tissues and, as predicted, splanchnic tissues had faster rates of isotopic incorporation and thus shorter retention times than structural tissues. We found that one-compartment models supported isotopic incorporation data better in breath, excreta, red blood cells, bone collagen, and claw tissues. However, data in plasma, intestine, liver, pectoralis muscle, gizzard, and intestine tissues supported two-compartment models. More importantly, the inferences that we derived from the two types of models differed. Two-compartment models estimated longer (13)C residence times, and smaller tissue to diet differences in isotopic composition, than one-compartment models. Our study highlights the importance of considering both one- and multi-compartment models when interpreting laboratory and field isotopic incorporation studies. It also emphasizes the opportunities that measuring several tissues with contrasting isotopic residence times offer to elucidate animal diets at different time scales.
authors.affiliation: Department of Zoology and Physiology, University of Wyoming, Laramie, WY 82071, USA. scarlet@uwyo.edu
authors.forename: Scott A
authors.initials: SA
authors.lastname: Carleton
authors.forename: Leona
authors.initials: L
authors.lastname: Kelly
authors.forename: Richard
authors.initials: R
authors.lastname: Anderson-Sprecher
authors.forename: Carlos Martínez
authors.initials: CM
authors.lastname: del Rio
mesh_terms: D000284:Administration, Oral; D000818:Animals; D002247:Carbon Isotopes / Q000008:administration & dosage* / Q000493:pharmacokinetics*; D003198:Computer Simulation; D008657:Metabolic Clearance Rate; D008954:Models, Biological; D009928:Organ Specificity; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D046370:Sparrows / Q000378:metabolism*; D014018:Tissue Distribution
chemical_list: D002247:Carbon Isotopes