Distortion product otoacoustic emissions in frogs: correlation with middle and inner ear properties.

Four frog species, Rana pipiens, Scaphiopus couchii, Xenopus laevis and Bombina orientalis, were examined for distortion product otoacoustic emissions (DPOAE). These species were chosen for their diverse otic morphologies. Rana has a well-developed caudal extension of the amphibian papilla within the inner ear; Scaphiopus, Xenopus and Bombina do not. Rana and Scaphiopus have a tympanic middle ear, Xenopus has a subcutaneous tympanic disk and Bombina has only an operculum. DPOAEs were present in Rana and Xenopus, with amplitudes up to 55 and 20 dB SPL, respectively. DPOAEs could be detected in neither Scaphiopus nor Bombina. These results show that (1) a well-developed caudal extension is not necessary for generation of DPOAEs, and (2) a tympanic middle ear is neither required nor sufficient to have DPOAEs.