Data of the tympanum and auditory sensitivity in two torrent frogs

Tympanic middle ears are important for anuran hearing on land; however, many species are observed to lose part or all of the tympanic apparatus. Some researchers have compared eared anurans' hearing sensitivity with earless species that produce calls and communicate with acoustic signals. Some anurans, however, lack both calling behaviour and well-developed tympanic membranes, and it is unclear whether they have fewer hearing perception-based selection pressures and how their hearing differs from closely related species with a developed acoustic communication system. Here, we compared the tympanic membranes of two sympatric sibling species living in noisy streams and showed that Hainan torrent frogs (Amolops hainanensis) were not only “dumb” but also had a vestigial eardrum that was smaller than that of little torrent frogs (Amolops torrentis) possessing a developed acoustic communication system. Then, we measured their auditory brainstem responses (ABRs) and compared the differences in ABR thresholds and latencies. Our results suggested that the two species exhibited significant differences in hearing sensitivity. A. hainanensis had higher thresholds and longer initial response times than A. torrentis at lower frequencies. The mechanical foundation and mechanism of such hearing changes require further study.