Honors Program Theses


Open Access Honors Program Thesis

First Advisor

Nathan Bird


Weberian apparatus--Effect of chemicals on; Endocrine disrupting chemicals--Physiological effect; Estrogen--Physiological effect;


Proper vertebrate development is controlled by a tightly regulated sequence of gene activation and repression. Exposure to both endogenous (hormones, gene products) and exogenous (environmental chemicals, toxins, etc.) substances during development can have profound effects on morphology by altering growth, cell fate, cell differentiation, and cell migration. Waterways have long been hot-spots for chemical and toxin accumulation, due to runoff and waste dumping. Growing concern is being paid to endocrine disruptors, like estrogen (17β-estradiol), which are found in increasing levels in rivers and streams. Endocrine disruptors are known to cause a varied number of defects in fish species, but the effect of estrogen on early vertebral development is unknown. In this study, the effect of exogenous estrogen (17β-estradiol) on development of the zebrafish Weberian apparatus is examined. The Weberian apparatus is an evolutionary adaptation of the four anteriormost vertebrae, and is unique to otophysan fishes (minnows, catfishes, characins, and South American electric eels). The function of the Weberian apparatus is to relay and amplify sound pressure changes from the gas bladder to the inner ear through physical coupling, and is hypothesized to be an independent developmental and evolutionary module, separate from ancestral vertebrae. High-dose estrogen proved lethal to larval zebrafish. Lower concentrations and shortened exposure times produced no morphological abnormalities within the cartilage elements of the Weberian apparatus, and overall effect on cranial cartilages was inconclusive. In addition, growth rates were not different across treatment groups. Results suggest that the Weberian apparatus may be immune to low doses of estrogen during early larval development, but given the overall lack of morphological effects across the body, immunity may not be limited to the Weberian apparatus alone.

Year of Submission



Department of Biology

University Honors Designation

A thesis submitted in partial fulfillment of the requirements for the designation University Honors

Date Original


Object Description

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