Date of Award

May 2015

Degree Type

Thesis

Degree Name

Master of Science

Department

Freshwater Sciences and Technology

First Advisor

Michael J. Carvan, III

Committee Members

Brian S. Shepherd, Matthew Smith

Keywords

Methylmercury, Reproduction, RNA-seq, Yellow Perch, Zebrafish

Abstract

This study sought to evaluate the effects of dietary MeHg exposure on female teleost reproduction and phenotypically-anchor gene dysregulation in adult yellow perch (Perca flavescens) and zebrafish (Danio rerio) in order to establish relevant biomarkers relating exposure and subsequent reproductive effects. Yellow perch were used in the study for their socioeconomic importance within the Great Lakes basin, and their significance to the food web. Utilization of zebrafish allowed for a detailed analysis of the molecular effects of MeHg and established its relevance as a model for other fish species. MeHg exposures at environmentally relevant levels were done in zebrafish for a full life cycle and in adult yellow perch for twenty weeks, capturing early seasonal ovarian development. RNA-seq elucidated the effects of exposure on gene expression and determined putative molecular mechanisms for negative reproductive impacts in zebrafish. In zebrafish, several genes involved in reproductive processes were shown to be dysregulated by RNA-seq and QPCR, but no significant phenotypic or physiological changes were observed with ovarian staging, fecundity, or embryo mortality. Yellow perch did not appear to be affected by MeHg, either at a molecular level, as assessed by QPCR of eight genes in the pituitary, liver, and ovary tissue, or a physiological level, as seen with ovarian somatic index and circulating estradiol. Lack of impact in yellow perch hinders the characterization of a biomarker, limits the usefulness of zebrafish as a model, and suggests that the reproductive sensitivity to environmentally relevant levels of MeHg differs between yellow perch and zebrafish.

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