Hearing sensitivity is more relevant to acoustic conspicuousness than to mechanical constraints in crambid moths

Moths evolved tympanal hearing organs to detect the echolocation calls of predatory bats. Moths’ auditory responses have been examined mainly for their sensitivity to the frequencies of bat cries: tympanate moths are basically tuned to the call frequencies of sympatric bats. Here, we add the finding that hearing sensitivity to ‘pulse duration’ in cram- bid moths is also affected by predation pressure from echolocating bats. Analysis of interspecific variation showed that minimum auditory thresholds had a significantly negative relationship with the forewing surface area, that is, acoustic conspicuousness to bat sonar, but no relationship with head width, which was assumed to correlate with tympanal organ size. Auditory thresholds increased as pulses shortened in the 1–10 ms duration range, and conspic- uous moths with larger wing areas had lower thresholds than smaller moths. By contrast, ‘intraspecific’ variation, within a single population of the lurcerne moth, revealed no relationship between forewing area and any auditory characteristics. Moth hearing adapts to the echolocation pulse duration of sympatric bat communities, suggesting that evolutionary modification of hearing sensitivity is related to acoustic conspicuousness based on moth wing area.