Teresa A. Bryan

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.

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

A previous study from our laboratory examining development in neonatal alligators from polluted Lake Apopka, Florida, 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 examine differences in alligators collected as eggs from these two populations and raised under similar conditions for 1 yr. Egg hatch rates did not differ between lake populations; however, posthatching 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 lake populations 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.