Male anuran amphibians (frogs and toads) use auditory (Bogert, 1960; Littlejohn, 1977; Wells, 1977; Gerhardt and Schwartz, 1995) and visual (for a review, see Hödl and Amézquita, 2001) cues to attract conspecific females and to defend territories against potential conspecific intruders. In most species of anuran, males are vocal and females are not, representing a clear example of a behavioral difference between the sexes. Males and females may also exhibit external morphological and other differences. For example, secondary sexual characteristics are traits other than those associated with the gonads and their ducts that differ between the sexes (Noble, 1931). The development of secondary sexual characteristics, resulting in sexual dimorphism, is a common phenomenon among the anurans (duToit, 1943). These characteristics may persist throughout the adult life of the animal; for example, the sexually dimorphic size of the tympanic membrane in some anuran species, such as the North American bullfrog Rana catesbeiana, in which the tympanic membrane of the male is larger than that of the female (Shofner and Feng, 1981; Hetherington, 1994; Purgue, 1997). Other examples of permanent secondary sexual characteristics are the bright coloration of males of Bufo periglenes compared with the females (Savage, 1967) and the unique frontal swellings on the head of male Rana pileata (Noble, 1931). In contrast, some species have ephemeral secondary sexual characteristics that appear only during the breeding season, in which case their expression is presumably under hormonal control. These include the nuptial pads of many male frogs and toads (Klemens, 1997), the prepollical spines on males of Hyla rosenbergi (Kluge, 1981) and the labial spines of 1223 The Journal of Experimental Biology 204, 1223–1232 (2001) Printed in Great Britain © The Company of Biologists Limited 2001 JEB3235 During the breeding season, each tympanic membrane of males of the Old World treefrog Petropedetes parkeri is decorated with a single, prominent, fleshy tympanic papilla. The tympanic papilla, located dorsally on the tympanic membrane, is covered by an epidermal surface and is composed of non-ossified, spongiform tissue containing a number of globular, fluid-filled vesicles 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 vibration 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 than that of a point diametrically opposite on the ventral half of the tympanic membrane. The close agreement between the dominant frequency of the call and the frequency of the maximum spectral peak of the Fast Fourier Transform of the impulse response of the eardrum is consistent with the use of the eardrum in this species both as a call receiver and as a call radiator, similar 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 importance of membrane tension as a dominant factor in the vibratory behavior of the eardrum. During normal positive-pressure breathing, the tympanic papillae move conspicuously, suggesting a possible rôle as a visual signal. Key words: tympanic membrane, Ranidae, Cameroon, Petropedetes parkeri, columella, tympanic papilla, communication. Summary Introduction FUNCTIONAL CONSEQUENCES OF A NOVEL MIDDLE EAR ADAPTATION IN THE CENTRAL AFRICAN FROG PETROPEDETES PARKERI (RANIDAE) PETER M. NARINS 1, *, EDWIN R. LEWIS 2 , ALEJANDRO P. PURGUE 1, ‡, PHILLIP J. BISHOP 3, §, LESLIE R. MINTER 4 AND DWIGHT P. LAWSON 5, ¶ 1 Department of Physiological Science, University of California, Los Angeles, 405 Hilgard Avenue, Los Angeles, CA 90095, USA, 2 Department of Electrical Engineering and Computer Science, University of California, Berkeley, CA 94270, USA, 3 Department of Zoology, University of the Witwatersrand, Johannesburg, Republic of South Africa, 4 Department of Medical Science, University of the North, Sovenga, Republic of South Africa and 5 Department of Biology, University of Texas at Arlington, Arlington, TX 76019, USA *e-mail: pnarins@ucla.edu ‡Present address: Bioacoustics Research Program, 159 Sapsucker Woods Road, Ithaca, NY 14850, USA. §Present address: Department of Zoology, University of Otago, Dunedin 9030, New Zealand. ¶Present address: Zoo Atlanta, 800 Cherokee Avenue S.E., Atlanta, GA 30315, USA. Accepted 3 January; published on WWW 15 March 2001