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Date Permissions Signed


Date of Award

Fall 2022

Document Type

Masters Thesis

Degree Name

Master of Science (MS)



First Advisor

Cooper, W. James, 1969-

Second Advisor

Pollard, Dan A.

Third Advisor

Zinkgraf, Matthew


Jaw shape often plays a significant role in determining feeding niche. Changes to jaw development can alter feeding mechanics and affect an organism’s ability to acquire and/or process food. Derived patterns of jaw morphogenesis are therefore frequently associated with evolutionary shifts in trophic ecology. Changes in thyroid hormone signaling can have strong developmental effects on many aspects of vertebrate anatomy including the shape of the lower jaws. Zebrafish mutants (opallusb1071) are hyperthyroid and typically undergo excessive mandible elongation. However, hyperthyroid opallus do not always develop elongated lower jaws. This mutant line was maintained at separate universities for many years, resulting in the establishment of a short-jawed phenotypic variant. It was originally thought that hyperthyroidism induced elongation of the mandibles in opallus during development, however, the short-jawed phenotypic variant suggests that the developmental determinants of mandible length are much more complicated. These two phenotypes in opallus provided an excellent opportunity to begin work towards investigating the developmental controls of mandible length in the zebrafish and its danionine relatives. To achieve our aims, we have 1) estimated the heritability of mandible length in opallus zebrafish; 2) predicted the additive genetic contributions of each parent fish to facilitate future genetic mapping studies; and 3) used an enzyme-linked immunosorbent assay (ELISA) to compare thyroid hormone levels in opallus and wildtype zebrafish tissues. We determined that corrected mandible length was heritable in opallus zebrafish and have identified the sire and dam to use for future genetic mapping and quantitative trait locus analysis. We also found that the thyroid hormone levels within the tissues of wildtype and opallus fish were not in agreement with results of previous studies using ELISA techniques, though this was likely due to kit selection errors.




Zebrafish, Evo-Devo, Heritability Study, Narrow Sense Heritability, Mandible Length, Thyroid Hormone, Cranial Development


Western Washington University

OCLC Number


Subject – LCSH

Zebra danio--Morphogenesis; Zebra danio--Endocrinology; Mandible; Hyperthyroidism; Biological assay




masters theses




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