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Date of Award


Document Type

Thesis - Pacific Access Restricted

Degree Name

Master of Science (M.S.)


Biological Sciences

First Advisor

Marcos Gridi-Papp

First Committee Member

Ryan L. Hill

Second Committee Member

Lisa A. Wrischnik


Polyploidy is the presence of more than two sets of chromosomes. Polyploidy can be fatal, but when tolerated it always results in increased cell size. Polyploid vertebrates are not larger than their diploid counterparts, despite having larger cells, due to cellular rearrangements. An anuran example was investigated to determine potential effects of polyploidy on the process of hearing. The North American gray treefrogs, Hyla chrysoscelis and Hyla versicolor, are nearly identical with the exception that the latter is tetraploid. Morphology, hearing performance, and histology of the ears were assessed to identify differences in the tuning and sensitivity of hearing between these two species. Performance was measured as vibration of eardrums, distortions by hair cells in the inner ears, and electrical activity in an auditory nucleus of the brain. All morphological features were slightly larger in H versicolor than H chrysoscelis; including SVL, body mass, interaural distance, and eardrum diameter. Hearing sensitivity did not differ between the two species, while tuning differed at specific regions in the hearing pathway. Laser

vibrometry revealed that spectral sensitivities at the eardrum and body wall were similar between the two species. Distortion-product otoacoustic emissions revealed a significant difference in tuning of the distortions produced by the hair cells, however, in which H versicolor had greater sensitivity to lower frequencies. This difference was supported by the observation of larger hair cell nuclei in the auditory sensory organs of H versicolor. Tuning at the midbrain was identical between the two species, suggesting that increased cell size biases the tuning of hair cell distortions more than their spectral sensitivity. Alternatively, a compensatory mechanism could prevent the lower tuning of hair cells from being expressed in the brain of H versicolor. Either explanation could involve selection to keep the tuning of hearing matched to the frog's conspecific advertisement call.



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