EFFECT OF TEMPERATURE UPON AUDITORY-THRESHOLDS IN 2 ANURAN SPECIES, BOMBINA V VARIEGATA AND O ALYTES-OBSTETRICANS (AMPHIBIA, DISCOGLOSSIDAE)

Because it seemed likely that temperature affects not only the calling mechanism of anurans, but their auditory systems as well, we have measured the thresholds of Bombina variegata variegata and Alytes obstetricans obstetricans at 5°, 12°, 20° and 28°C by recording multiple-unit activity from the torus semicircularis. An increase in temperature from 5° to 28°C shortened the latencies considerably. In Bombina v. variegata latencies fell from an average of 32 ms to 13 ms (600 Hz), and in Alytes o. obstetricans from an average of 22 ms to 11 ms (500 Hz). At frequencies below 500 Hz the decrease was still greater. Latency was also dependent on frequency, being shorter with high-frequency tones. At 5°C the auditory neurons of Bombina are rather insensitive and respond irregularly. At 12°C and at 20°C sensitivity is markedly increased. The minimum threshold in males was at 400-500 Hz (49 dB SPL), and that of females was at 450 Hz (47 dB SPL). There was no further increase in sensitivity at 28°C. In Alytes the auditory neurons were fully functional even at 5°C. At this temperature the audiogram had sensitivity maxima at 300, 1,100-1,300 and 1,800 Hz. In both males and females an increase in temperature to 20°C caused an extraordinary increase in sensitivity, primarily in the low-frequency range; the minimum threshold, at 400 Hz, was 44 dB SPL in males and 41 dB SPL in famales. In the intermediate frequency range there was also a marked increase in sensitivity, but not in the high-frequency range, where the best frequency was 1,800 Hz. At 28°C the threshold to low-frequency tones was increased. © 1979 Springer-Verlag.