ORIGINAL PAPER W. Ho¨dl Æ A. Ame´zquita Æ P. M. Narins The ro ˆ le of call frequency and the auditory papillae in phonotactic behavior in male Dart-poison frogs Epipedobates femoralis (Dendrobatidae) Received: 31 December 2003 / Revised: 27 May 2004 / Accepted: 28 May 2004 / Published online: 29 July 2004 Ó Springer-Verlag 2004 Abstract Territorial males of the pan-Amazonian Dart- poison frog, Epipedobates femoralis, are known to present stereotypic phonotactic responses to the play- back of conspecific and synthetic calls. Fixed site attachment and a long calling period within an envi- ronment of little temperature change render this terres- trial and diurnal pan-Amazonian frog a rewarding species for field bioacoustics. In experiments at the field station Arataı¨, French Guiana, we tested whether the prominent frequency modulation of the advertisement- call notes is critical for eliciting phonotactic responses. Substitution of the natural upward sweep by either a pure tone within the species frequency range or a reverse sweep did not alter the males’ phonotactic behavior. Playbacks with artificial advertisement calls embedded in high levels of either low-pass or high-pass masking noise designed to saturate nerve fibers from either the amphibian papilla or basilar papilla showed that male phonotactic behavior in this species is subserved by activation of the basilar papilla of the inner ear. Keywords Acoustic playback experiment Æ Anura Æ Call frequency modulation Æ Phonotaxis Æ Territorial behavior Abbreviations FM: Frequency modulated Æ AP: Amphibian papilla Æ BP: Basilar papilla Introduction Male anuran vocalizations serve to attract conspecific females and to regulate male spacing (Wells 1977; Rand 1988). They are often periodic, discrete signals, stereo- typed in both the frequency and time domains (however, for variation in advertisement call complexity see Sch- wartz and Wells 1984; Ryan 1985; Wells 1988; Narins et al. 1998, 2000; Feng et al. 2002). Not all of the ste- reotyped spectral and temporal properties are critical for intraspecific communication (Gerhardt 1988) nor is it likely that a single call character is responsible for call recognition, but rather that a combination of characters is involved (Schwartz 1986, 1987; Gerhardt and Doherty 1988; Wells 1988; Gerhardt and Huber 2002). The frog inner ear contains three organs that respond to airborne sound—the amphibian papilla (AP), the basilar papilla (BP) and the sacculus (S), although only the first two are known to subserve long-distance sound reception. Acute frequency resolution occurs only for energy falling within the range of sensitivity of the AP (Narins and Capranica 1980; Zakon and Wilczynski 1988; Lewis and Narins 1999). Nerve fibers innervating AP hair cells exhibit V-shaped tuning curves with distinct best frequencies ranging from ca. 0.1 kHz to 1.0–1.4 kHz. In contrast, BP fibers are broadly tuned and exhibit a narrow range of best frequencies that typically falls above 1.0 kHz (Zakon and Wilczynski 1988). It is currently thought that the peripheral auditory system of anurans is generally specialized to process species-specific communication calls but not exclusively dedicated to them (Feng et al. 1990). This is also consistent with the idea that sensitivity to environmental sounds other than the species-specific advertisement call (e.g., prey-generated sounds, hetero- specific calls, abiotic noise) would clearly confer a selective advantage to the individual possessing it. Typically, males alter their calling/behavioral pattern when stimulated by playbacks of conspecific calls at su- prathreshold levels (Zelick and Narins 1982; Ryan 1986; Wells 1988; Grafe 1996; Lewis et al. 2001). Overt behav- W. Ho¨dl (&) Institute of Zoology, University of Vienna, Althanstrasse 14, 1090 Wien, Austria E-mail: walter.hoedl@univie.ac.at Tel.: +43-1-427754495 Fax: +43-1-42779544 A. Ame´zquita Departamento de Ciencias Biolo´gicas, Universidad de Los Andes, Bogota´, Colombia P. M. Narins Departments of Physiological Science and Organismic Biology, Ecology and Evolution, University of California Los Angeles, Los Angeles, CA 90095, USA J Comp Physiol A (2004) 190: 823–829 DOI 10.1007/s00359-004-0536-1