Convergent evolution of anti-bat sounds
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Bats and their insect prey rely on acoustic sensing in predator prey encounters—echolocation in bats, tympanic hearing in moths. Some insects also emit sounds for bat defense. Here, we describe a previously unknown sound-producing organ in Geometrid moths—a prothoracic tymbal in the orange beggar moth (Eubaphe unicolor) that generates bursts of ultrasonic clicks in response to tactile stimulation and playback of a bat echolocation attack sequence. Using scanning electron microscopy and high-speed videography, we demonstrate that E. unicolor and phylogenetically distant tiger moths have evolved serially homologous thoracic tymbal organs with fundamentally similar functional morphology, a striking example of convergent evolution. We compared E. unicolor clicks to that of five sympatric tiger moths and found that 9 of 13 E. unicolor clicking parameters were within the range of sympatric tiger moths. Remaining differences may result from the small size of the E. unicolor tymbal. Four of the five sympatric clicking tiger moth species were unpalatable to bats (0–20 % eaten), whereas E. unicolor was palatable to bats (86 % eaten). Based on these results, we hypothesize that E. unicolor evolved tymbal organs that mimic the sounds produced by toxic tiger moths when attacked by echolocating bats.
KeywordsBatesian mimicry Bioacoustics Predator defense Sound production Tymbal organ
We thank the staff of the Southwestern Research Station for coordination of field research, and Nick Dowdy for field assistance. William Conner and Gerald Carter reviewed a former version of this manuscript. Funding was provided by the National Science Foundation (Grant Number IOS-0951160), the American Museum of Natural History (Theodore Roosevelt Grant) and by an institutional training grant (UMD T32 DC-00046) from the National Institute of Deafness and Communicative Disorders of the National Institutes of Health. All research on vertebrates was approved by the Wake Forest University Animal Care and Use Committee (IACUC #A09-094).
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