Dieldrich S. Bermudez

Altered neonatal development and endocrine function in Alligator mississippiensis associated with a contaminated environment

Abstract Reduced reproductive success, altered reproductive tract development, and differences in circulating hormones have been documented in American alligators (Alligator mississippiensis) from Lake Apopka, FL, compared to less contaminated sites, such as the Lake Woodruff National Wildlife Refuge, FL. Comparative studies among alligators of varying size and age suggest that in ovo contaminant-induced alterations of endocrine function are further modified during postembryonic development and/or through environmental exposure. In the present study, we examined developmental and endocrine-related indices in neonatal (age, <1 mo) alligators from Lake Apopka in comparison to those of a reference population (Lake Woodruff), thereby limiting contaminant exposure to that derived via maternal contribution. We compared several reproductive and developmental parameters, including hatching success, primary sex determination, and somatic indices. Furthermore, we examined circulating testosterone concentrations and aromatase activity in an effort to establish relative gonadal endocrine function shortly after hatching. Finally, we compared phallus size among males and oviduct epithelial cell height (ECH) among females (androgen- and estrogen-dependent tissues, respectively). Significant differences between populations were noted for body size and spleen somatic index. Neonatal alligators from Lake Apopka exhibited higher plasma testosterone, but no differences were detected in gonadal aromatase activity compared to Lake Woodruff. Phallus tip length and cuff diameter were smaller in males from Lake Apopka, whereas no differences were noted in oviduct ECH. Our data establish basic indices of development and endocrine function in neonatal alligators before environmental exposure to contaminants. These results should begin to help separate developmental abnormalities resulting from in ovo exposure, presumably of maternal origin, from physiological alterations induced through environmental exposure to contaminants.

Gene expression patterns in juvenile American alligators (Alligator mississippiensis) exposed to environmental contaminants.

Reproductive and developmental abnormalities have been reported in the American alligator (Alligator mississippiensis) population from Lake Apopka, FL, that is chronically exposed to a complex mixture of environmental contaminants. To begin to understand the molecular mechanisms that could lead to the observed abnormalities of the reproductive and endocrine system, we quantified concentrations of the steroid hormones testosterone (T) and estradiol-17beta (E(2)) and expression of steroid hormone receptors and genes relating to steroidogenesis in gonadal tissue from juvenile alligators from three lakes in Florida using enzyme immunoassay and quantitative real-time polymerase chain reaction. Alterations of ESR2 (estrogen receptor beta) and SF1 (steroidogenic factor 1) mRNA expression in male gonadal tissue, without an observed difference in plasma concentrations of T, from the different lakes, begin to provide insight into potential mechanisms underlying the alterations of the reproductive system previously observed. Likewise, alterations in P450 aromatase and DAX1 (dosage-sensitive sex reversal, adrenal hypoplasia congenita critical region on the X chromosome, gene 1) mRNA expression, with elevated plasma E(2) concentrations in females, provide leads to the potential mechanisms modifying folliculogenesis and ovarian development. The investigation of these genes also helps clarify normal endocrine and reproductive system function in the American alligator.

Sex Steroid and Thyroid Hormone Receptor Expressions in the Thyroid of the American Alligator ( ALLIGATOR MISSISSIPPIENSIS ) During Different Life Stages

The expression of estrogen receptors, ESR1 (ERα) and ESR2 (ERβ), and androgen receptors (AR) in the thyroid gland has been reported in few vertebrate species other than a few mammals. This study reports the presence of sex steroid hormone receptors and thyroid receptors (ERα, ERβ, AR, TRα, and TRβ) in the thyroid gland of the American alligator at several life stages. It provides a semiquantification and distribution of ERα in the thyroid follicle cells using an immunohistochemical approach as well as reports quantitative differences in mRNA expression of ERα, ERβ, TRα, TRβ, and AR in the same tissue using quantitative real time‐PCR (Q‐PCR) with primers designed specifically for alligators. The thyroid tissue of the American alligator expresses ERα, ERβ, and AR at all of the life stages examined here although no statistically significant differences were observed between male and female in thyroid mRNA expression for any of the genes analyzed. No sexual dimorphism was observed in ERα immunostaining. No statistical analysis across life stages were performed due to confounding factor of season. J. Morphol. 2011.