Date of Award

Spring 2006

Project Type

Dissertation

Program or Major

Natural Resources and Environmental Studies

Degree Name

Doctor of Philosophy

First Advisor

Kimberly J Babbitt

Abstract

The prevalence of malformed amphibians and the association of high incidences of malformation with the presence of environmental contaminants have raised questions about the effects of environmental contaminants on the development of larval amphibians. The potential endocrine disrupting effects of pesticides suggest that the reproductive and developmental abnormalities observed in larval anurans may be due at least in part to impacts on the hypothalamic-pituitary-gonadal axis. The present studies investigate the effects of exposure to environmental contaminants including DDT and atrazine on the development, gonadal histology and reproductive steroidogenesis of larval anurans.

As previous monitoring at Great Bay National Wildlife Refuge (NWR), Newington, New Hampshire documented incidences of amphibian malformations at four sites contaminated with potentially endocrine active compounds, the present study utilized in situ exposures and laboratory toxicology experiments to determine if contaminants present in the sites affect amphibian development. Five intersex/mixed sex animals were produced in the enclosure experiment. Reproductive development and steroidogenic capacity of male metamorphs from Reference Beaver Pond were more advanced relative to males from the other sites. In the laboratory sediment exposure experiment, reproductive development was altered by contaminants present in the sediments and the degree of alteration was related to nominal DDT concentrations. The proportion of animals exhibiting testicular oocytes increased, whereas androgen concentrations and the proportion of gonadal tissue exhibiting advanced stages of spermatogenesis decreased as DDT concentration increased. This work indicates that environmental contaminants may alter reproductive development.

The potential for atrazine to alter the development, gonadal histology, and reproductive steroidogenesis of two species of anurans was investigated in two laboratory experiments. Exposure to atrazine increased tadpole growth and developmental rates for Hyla versicolor, but not for Rana pipiens, whereas atrazine exposure did not result in altered gonadal development for either species. None of the H. versicolor metamorphs exhibited gonadal abnormalities, while testicular oocytes occurred in R. pipiens metamorphs from all treatments, including the controls. Suggesting that testicular oocytes may be a natural ontogenetic occurrence in some species. Establishing the normal pattern of anuran reproductive development is necessary to clarify the effects of endocrine disrupting contaminants.

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