Auditory changes in noctuid moths endemic to a bat‐free habitat

If the ears of moths exist primarily to detect the echolocation calls of hunting bats, endemic moths in bat‐free areas (i.e., species that have evolved in the absence of the selection pressure maintaining ears) should exhibit signs of deafness. Noctuid moths from the Pacific islands of French Polynesia, a site that has never possessed bats, were sampled and electrophysiologically analysed to test this hypothesis. The auditory sensitivities of seven endemic and twelve immigrant species, captured from the islands of Tahiti, Moorea, and Hiva Oa, were compared. Both classes possess neurally responsive ears, but endemics are significantly deafer than immigrants at frequencies above 35 kHz. This form of deafness is similar to other moths presumably released from the selection pressure of bat predation. I conclude that endemic moths at this site exhibit preliminary stages of deafness and that, considering their small cellular investment, ears in moths will be lost at a slower rate than more complex sensory organs.