Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

Urinary iodine and stable isotope analysis to examine habitat influences on thyroid hormones among coastal dwelling American alligators



Ashley S. Boggs-Russell, Heather J. Hamlin, James C. Nifong, Brittany L. Kassim, Russell H. Lowers, Thomas M. Galligan, Stephen E. Long, Louis J. Guillette Jr.


The American alligator, a freshwater species, is known to forage in marine environments which 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 135 cm 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.
Environmental Science & Technology


thyroid hormones, triiodothyronine, thyroxine, urinary iodine, stable isotope, alligator, coastal ecology


Boggs-Russell, A. , Hamlin, H. , Nifong, J. , Kassim, B. , Lowers, R. , Galligan, T. , Long, S. and Guillette, L. (2015), Urinary iodine and stable isotope analysis to examine habitat influences on thyroid hormones among coastal dwelling American alligators, Environmental Science & Technology, [online], (Accessed April 19, 2024)
Created December 9, 2015, Updated February 4, 2020