title: Urinary iodine and stable isotope analysis to examine habitat influences on thyroid hormones among coastal dwelling American alligators.
abstract: The American alligator, generally a freshwater species, is known to forage in marine environments despite the lack of a salt secreting gland found in other crocodylids. Estuarine and marine foraging could lead to increased dietary uptake of iodine, a nutrient necessary for the production of thyroid hormones. To explore the influence of dietary iodine on thyroid hormone health of coastal dwelling alligators, we described the seasonal plasma thyroxine and triiodothyronine concentrations measured by radioimmunoassay and urinary iodine (UI) concentrations measured by inductively coupled plasma mass spectrometry. We also analyzed long-term dietary patterns through stable isotope analysis of scute tissue. Snout-to-vent length (SVL) was a significant factor among UI and stable isotope analyses. Large adult males greater than 135cm SVL had the highest UI concentrations but did not display seasonality of thyroid hormones. Alligators under 135 SVL exhibited seasonality in thyroid hormones and a positive relationship between UI and triiodothyronine concentrations. Isotopic signatures provided supporting evidence that large males predominantly feed on marine/estuarine prey whereas females showed reliance on freshwater/terrestrial prey supplemented by marine/estuarine prey. UI measurement provided immediate information that correlated to thyroid hormone concentrations whereas stable isotope analysis described long-term dietary patterns. Both techniques demonstrate that adult alligators in coastal environments are utilizing estuarine/marine habitats, which could alter thyroid hormone physiology.
authors.affiliation: National Institute of Standards and Technology, Environmental Chemical Sciences, 331 Fort Johnson Rd, Charleston, SC 29412, USA; Hollings Marine Laboratory, 331 Fort Johnson Rd, Charleston, SC 29412, USA. Electronic address: ashley.boggs@nist.gov.
authors.forename: Ashley S P
authors.initials: AS
authors.lastname: Boggs
authors.affiliation: University of Maine, School of Marine Sciences, 316 Murray Hall Orono, ME 04469, USA.
authors.forename: Heather J
authors.initials: HJ
authors.lastname: Hamlin
authors.affiliation: University of Florida, Fisheries and Aquatic Sciences, NW 71st Street, Gainsville, FL 32653, USA.
authors.forename: James C
authors.initials: JC
authors.lastname: Nifong
authors.affiliation: National Institute of Standards and Technology, Environmental Chemical Sciences, 331 Fort Johnson Rd, Charleston, SC 29412, USA; Hollings Marine Laboratory, 331 Fort Johnson Rd, Charleston, SC 29412, USA.
authors.forename: Brittany L
authors.initials: BL
authors.lastname: Kassim
authors.affiliation: National Aeronautics and Space Administration, InoMedic Health Applications Inc., SR 405, Kennedy Space Center, FL 32899, USA.
authors.forename: Russell H
authors.initials: RH
authors.lastname: Lowers
authors.affiliation: Hollings Marine Laboratory, 331 Fort Johnson Rd, Charleston, SC 29412, USA; Medical University of South Carolina, Department of Obstetrics and Gynecology, 331 Fort Johnson Rd, Charleston, SC 29412, USA.
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Galligan
authors.affiliation: National Institute of Standards and Technology, Environmental Chemical Sciences, 331 Fort Johnson Rd, Charleston, SC 29412, USA; Hollings Marine Laboratory, 331 Fort Johnson Rd, Charleston, SC 29412, USA.
authors.forename: Stephen E
authors.initials: SE
authors.lastname: Long
authors.affiliation: Hollings Marine Laboratory, 331 Fort Johnson Rd, Charleston, SC 29412, USA; Medical University of South Carolina, Department of Obstetrics and Gynecology, 331 Fort Johnson Rd, Charleston, SC 29412, USA.
authors.forename: Louis J
authors.initials: LJ
authors.lastname: Guillette
mesh_terms: D000489:Alligators and Crocodiles / Q000097:blood / Q000378:metabolism* / Q000652:urine; D000818:Animals; D004032:Diet; D017753:Ecosystem; D005260:Female; D005618:Fresh Water; D007455:Iodine / Q000652:urine*; D008297:Male; D013960:Thyroid Function Tests; D013961:Thyroid Gland / Q000502:physiology; D013974:Thyroxine / Q000097:blood*; D014284:Triiodothyronine / Q000097:blood*; D014481:United States
chemical_list: D014284:Triiodothyronine; D007455:Iodine; D013974:Thyroxine
keywords: American alligator; Stable isotope analysis; Thyroid hormone; Thyroxine; Triiodothyronine; Urinary iodine