Date of Award

1-2011

Degree Name

Doctor of Philosophy

Department

Biological Sciences

First Advisor

Dr. Charles Ide

Second Advisor

Dr. Bruce Bejcek

Third Advisor

Dr. Robert Eversole

Fourth Advisor

Dr. Susan Stapleton

Abstract

Atrazine is one of the two most commonly used herbicides in the US and it is the most studies are among the first to link physiological effects of atrazine to changes in tissue and gene expression in Xenopus laevis tadpoles. These studies provide the groundwork for future studies into the mechanisms behind responses to chemical stressors generating data resulting in a better understanding of how these chemicals affect us all. commonly found herbicide in ground water. As a result, a great deal of attention has been placed on its use and safety. It has also been implicated to play a role in the decline of frog populations worldwide.

This thesis reports results from studies into the effects of atrazine on developing tadpoles of the amphibian laboratory model, the African Clawed frog (Xenopus laevis). The levels of atrazine tested include levels found in field runoff (200 and 4 0 0 pg/L) and a low dose (25 pg/L) studied by others. During all exposures, growth, metamorphosis, fat body (a lipid storage organ) size and liver weights were measured. In selected studies, feeding behavior was recorded, microscopic evaluations were conducted, qRT-PCR was performed on selected genes, and ATP and ADP levels were measured.

The low-level exposure had no effect on tadpoles. Tadpoles exposed to runoff levels were smaller than unexposed controls by 3 days into the exposure and were still smaller at the end of the studies. Some groups also experienced slowed metamorphosis. Interestingly, appetite was not decreased in these tadpoles. Livers and fat bodies were also smaller at the end of exposure. Liver ADP:ATP ratios indicated these animals had some difficulty maintaining adequate energy levels. Using qRT-PCR, we showed changes in gene expression 24 hours into exposure. The genes affected were indicative of an early stress response to exposure. Clearly, acutely and chronically exposed tadpoles were compromised potentially decreasing their ability to survive the stresses of metamorphosis and reducing their reproductive fitness.

It is significant that changes were noted within 72 hours of exposure since, in the field, tadpoles could encounter similar exposure rates. Therefore, these data are relevant to field conditions. These

studies are among the first to link physiological effects of atrazine to changes in tissue and gene expression in Xenopus laevis tadpoles. These studies provide the groundwork for future studies into the mechanisms behind responses to chemical stressors generating data resulting in a better understanding of how these chemicals affect us all.

Access Setting

Dissertation-Open Access

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