Functional consequences of a novel middle ear adaptation in the central African frog Petropedetes parkeri (Ranidae)

During the breeding season, each tympanic membrane of males of the Old Worl d treefrog Petropedetes parkeri is decorated with a single, prominent, fles hy tympanic papilla, The tympanic papilla, located dorsally on the tympanic membrane, is covered by an epidermal surface and is composed of non-ossifi ed, spongiform tissue containing a number of globular, fluid-filled vesicle s found at highest density near the papillar tip. These vesicles appear to have exit pores and are probably simple alveolar exocrine glands. Injecting sound into the pressurized vocal cavity of the male and measuring the vibr ation velocity response of the tympanic membrane revealed that from 0.3 to 2.0 kHz the tympanic papilla velocity amplitude is on average 20 dB lower t han that of a point diametrically opposite on the ventral half of the tympa nic membrane, The close agreement between the dominant frequency of the cal l and the frequency of the maximum spectral peak of the Fast Fourier Transf orm of the impulse response of the eardrum is consistent with the use of th e eardrum in this species both as a call receiver and as a call radiator, s imilar to the function suggested for the eardrum of the male bullfrog Rana catesbeiana. Unexpectedly, surgically removing the tympanic papilla lowered the frequency of the peak vibrational amplitude, testifying to the importa nce of membrane tension as a dominant factor in the vibratory behavior of t he eardrum. During normal positive-pressure breathing, the tympanic papilla e move conspicuously, suggesting a possible role as a visual signal.