Auditory Sensitivity in Primitive Anurans of the Genus Discoglossus

The auditory sensitivity of frogs Discoglossus (Alytidae) was measured and compared with the known spectral characteristics of their vocalizations, to assess evolutionary patterns of sound communication in these primitive anurans. Multi-unit recordings in the Torus semicircularis of 6 D. pictus, and 2 D. galganoi show two regions of enhanced sensitivity, below 0.5 kHz and at ca. 1.6 kHz, with minimum thresholds at ca. 40 and 50 dB SPL, respectively. The high frequency sensitivity region is tuned to frequencies higher than the calls reported for this genus, with dominant frequencies below 1 kHz. These audiogram characteristics were similar to those measured in a former study in Iberian Alytes toads. However, auditory thresholds to calls of Alytidae were higher in Discoglossus relative to those measured in A. cisternasii, A. obstetricans and A. dickhilleni in response to vocalizations of one Discoglossus and two Alytes species. The relatively high auditory thresholds of Discoglossus, together with the low amplitude of their vocalizations and the detuning between call spectra and auditory sensitivity restrict their sound communication to short distances. Such mismatch is likely a derived trait in the evolutionary history of the genus, as occurs in other anuran groups.