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Auditory mechanics and sensitivity in the tropical butterfly Morpho peleides (Papilionoidea, Nymphalidae)
Kathleen M. Lucas, James F. C. Windmill, Daniel Robert, Jayne E. Yack


The ears of insects exhibit a broad functional diversity with the ability to detect sounds across a wide range of frequencies and intensities. In tympanal ears, the membrane is a crucial step in the transduction of the acoustic stimulus into a neural signal. The tropical butterfly Morpho peleides has an oval-shaped membrane at the base of the forewing with an unusual dome in the middle of the structure. We are testing the hypothesis that this unconventional anatomical arrangement determines the mechanical tuning properties of this butterfly ear. Using microscanning laser Doppler vibrometry to measure the vibrational characteristics of this novel tympanum, the membrane was found to vibrate in two distinct modes, depending on the frequency range: at lower frequencies (1–5 kHz) the vibration was focused at the proximal half of the posterior side of the outer membrane, while at higher frequencies (5–20 kHz) the entire membrane contributed to the vibration. The maximum deflection points of the two vibrational modes correspond to the locations of the associated chordotonal organs, suggesting that M. peleides has the capacity for frequency partitioning because of the different vibrational properties of the two membrane components. Extracellular nerve recordings confirm that the innervating chordotonal organs respond to the same frequency range of 1–20 kHz, and are most sensitive between 2 and 4 kHz, although distinct frequency discrimination was not observed. We suggest that this remarkable variation in structure is associated with function that provides a selective advantage, particularly in predator detection.


  • Supplementary material available online at http://jeb.biologists.org/cgi/content/full/212/21/3533/DC1

  • We thank Ed Bruggink (Carleton) and Vicky Pook (Bristol) for help rearing the butterflies. We thank Dr J. Sueur and an anonymous reviewer for their helpful suggestions on the article. This work was funded by a Journal of Experimental Biology Travelling Fellowship to K.M.L., the Canadian Foundation for Innovation, Ontario Innovation Trust, and the Natural Science and Engineering Research Council to J.E.Y, and the BBSRC to J.F.C.W. and D.R.

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