The Effect of Cell Size on Auditory Morphology and Tuning in Gray Treefrogs

For the brain to perceive sound, signals have to be transmitted across the eardrum, ossicles, inner ear fluid, hair cells and nerves. The hearing properties of frogs are affected by the mechanical properties of tissues in the auditory chain. If the sizes of the cells vary, the tuning of the auditory structures formed by them might be affected. Two gray treefrogs: Hyla versicolor and Hyla chrysoscelis, are identical, but the former has twice the number of chromosomes than the later, and chromosomal duplication always results in increased cell size. We hypothesized that the larger cells of auditory elements in the tetraploid H. versicolor make it more sensitive to lower frequencies than diploid H. chrysoscelis. We are characterizing the auditory morphology of both frogs to relate it to their hearing performance. In order to obtain quantitative results, we have been dissecting out the inner ear, middle ear, and auditory ossicles. These tissues are then decalcified and embedded in paraffin, sectioned in the microtome and stained with hematoxylineosin. These methods have been initially tested in Rana pipiens, to establish decalcification procedures involving acids, EDTA, and microwaving. We are currently obtaining the sections for gray treefrogs and these results should allow us to determine relationships between polyploidy, cell size, auditory morphology and hearing performance. These data should advance our understanding of ear design and explain how morphological differences in the ears result in the hearing sensitivities of various species