Circadian Rhythm and Intersexual Differences in Auditory Frequency Sensitivity in Emei Music Frogs

In anurans, calling behaviour is strongly seasonal and circadian. Previous studies have revealed that auditory sensitivity in frogs exhibits seasonal plasticity, and electroencephalographic signals exhibit highly correlated circadian patterns; of which, the circadian rhythm remains unknown. In this study, the circadian rhythm and intersexual differences of auditory sensitivity were tested in the Emei music frog (Nidirana daunchina). This was achieved by comparing thresholds and latencies of auditory brainstem responses (ABRs) evoked by tones and clicks stimuli between male and female frogs during the day and at night, respectively. Our results revealed that both auditory thresholds and latencies had no differences between day and night except the latencies in 3.5-4.0 kHz frequencies. However, the thresholds of tone pip evoked ABRs differed significantly between male and female frogs from 25 to 5.0 kHz. This demonstrated that the auditory sensitivity of Emei music frogs exhibits sexual dimorphism at high frequencies, with female frogs exhibiting greater auditory sensitivity than that of male frogs. Simultaneously, the power spectra of male advertisement calls are matched well with the frequency range of auditory sensitivity in male and female frogs, which supports the matched filter hypothesis. Our study enhances the understanding of circadian plasticity and sexual dimorphism of auditory sensitivity in frogs.