The Relationship Between Auditory Morphology and Tuning in Three Species of Frogs

Rana pipiens is a frog that has been extensively used as a model to learn about the auditory capabilities of anurans. Due to the lack of comparative studies of the auditory system among frogs, we used R. pipiens as a reference to assess differences in ear morphology between species indigenous to other areas of the world, specifically Engystomops pustulosus (found in Central America), and Leptopelis flavomaculatus (found in Africa). Theoretically, there should be an inverse relationship between the size of a frog and the sound frequencies that it can hear and produce. Engystomops pustulosus, being the smallest of the three species, would hypothetically be tuned to the highest frequencies; likewise, the large R. pipiens would hear and produce sound at the lowest frequencies. Dissections were conducted to isolate the middle and inner ears. To compare species’ ear anatomy, histological methods were used which allow for precise measurement of cells and larger structures under the microscope. Tissues were fixated and decalcified, dehydrated, paraffin embedded, sectioned with a microtome, mounted onto slides, rehydrated, and finally, stained. The highly ossified nature of auditory structures required additional adjustment of the decalcification protocol, including acids, EDTA, and microwaving. The expected results are quantitative descriptions of the morphology of the auditory pathway, that should explain the size relations and specializations presented by the species in this study