Toxicology

Increased Post Hatching Mortality and Loss of Sexually Dimorphic Gene Expression in Alligators (Alligator mississippiensis) from a Contaminated Environment

Abstract
A previous study from our lab examining development in neonatal alligators from polluted Lake Apopka, FL, found numerous differences relative to neonates from a reference site, Lake Woodruff National Wildlife Refuge. We postulated that the differences were the result of organizational changes derived from embryonic exposure to environmental contaminants, and are related to the poor reproductive success reported in alligators from Lake Apopka. In this study we examined differences in alligators collected as eggs from these two populations and raised under similar conditions for one year. Egg hatch rates did not differ between lakes; however, post-hatching mortality was much higher among Lake Apopka hatchlings. Snout-vent length and body mass were greater in Lake Apopka hatchlings, but no differences were detected between lakes in thyroid, liver, and spleen mass corrected for body size, or in plasma concentrations of testosterone and estradiol. Males from Lake Woodruff exhibited greater relative expression of gonadal mRNA for steroidogenic factor 1 (Nr5a1) and steroidogenic acute regulatory protein (Star) than males from Lake Apopka. Alligators from Lake Woodruff also expressed all genes examined in a sexually dimorphic pattern. In contrast, mRNA expression did not differ between males and females from Lake Apopka for Nr5a1, Star, cytochrome P450 11A1 (Cyp11a1), and hydroxy-delta-5-steroid dehydrogenase, 3 beta- and steroid delta-isomerase 1 (Hsd3b1). Our results document persistent differences in development, survivorship, and gene expression in alligators from a contaminated environment. Because these animals were raised under similar laboratory conditions, the differences are most likely of embryonic origin and organizational in nature.

Key words: Toxicology • Estradiol • Gene regulation • Steroid hormones • Testosterone