Effects of environmental contaminants on development, sexual differentiation, and steriodogenesis in Alligator mississippiensis

Xenobiotics that interfere with normal endocrine function have been designated as endocrine-disrupting contaminants (EDCs). Environmental exposure to EDCs and adverse effects on development and reproductive physiology have been documented in numerous wildlife populations. In this dissertation, alligators from Lake Apopka, FL, are examined as a case study of a population chronically exposed to EDCs that has experienced poor reproductive success and compared to alligators from Lake Woodruff National Wildlife Refuge, a reference population of minimal anthropogenic influence that has exhibited consistently high reproductive success. In comparing parameters relevant to development and endocrine function between these two populations and with alligators experimentally exposed to various EDCs, two specific questions are addressed: (1) what endpoints, with regard to sexual differentiation and gonadal function, are affected during embryonic development by EDCs in the alligator, and (2) do these alterations persist beyond neonatal development?; Snout-vent length, body mass, and phallus size were significantly smaller in Lake Apopka neonates, which also exhibited higher plasma testosterone (T) concentrations compared to Lake Woodruff neonates. Embryonic exposure to estradiol at an egg incubation temperature that normally produces males resulted in females that exhibited intermediate gonadal aromatase activity relative to control males and females, and masculinized brain aromatase activity. A female biased sex ratio was observed among hatchlings exposed to p,p'-DDE at 100 parts per billion (ppb) wet egg mass, whereas no effect on sex determination was observed for toxaphene. Male neonates treated with 10 and 0.01 ppb toxaphene had higher plasma T concentration than control males. Significant post hatching mortality and lower mRNA concentrations for SF-1 and StAR, two genes coding for factors involved in the regulation of de novo steroidogenesis, were observed in 13-month old alligators from Lake Apopka compared to alligators from Lake Woodruff. In addition, juveniles from Lake Apopka exhibited a loss of sexual dimorphism in four of the six genes examined.; These data establish endpoints susceptible to perturbation by embryonic exposure to EDCs and provide evidence of persistent alterations in alligators relevant to reproduction. Future research is needed to determine the ability of individuals exposed to EDCs as embryos to reproduce successfully as adults.