Current Biology
Volume 16, Issue 24, 19 December 2006, Pages 2418-2423
Keeping up with Bats: Dynamic Auditory Tuning in a Moth
James Frederick Charles Windmill, Joseph Curt Jackson, Elizabeth
Jane Tuck, and Daniel Robert
Summary
Many night-flying insects evolved ultrasound sensitive ears in
response to acoustic predation by echolocating bats. Noctuid moths are
most sensitive to frequencies at 20-40 kHz [6], the lower range of bat
ultrasound. This may disadvantage the moth because noctuid-hunting
bats in particular echolocate at higher frequencies shortly before
prey capture and thus improve their echolocation and reduce their
acoustic conspicuousness. Yet, moth hearing is not simple; the ear's
nonlinear dynamic response shifts its mechanical sensitivity up to
high frequencies. Dependent on incident sound intensity, the moth's
ear mechanically tunes up and anticipates the high frequencies used by
hunting bats. Surprisingly, this tuning is hysteretic, keeping the ear
tuned up for the bat's possible return. A mathematical model is
constructed for predicting a linear relationship between the ear's
mechanical stiffness and sound intensity. This nonlinear mechanical
response is a parametric amplitude dependence that may constitute a
feature common to other sensory systems. Adding another twist to the
coevolutionary arms race between moths and bats, these results reveal
unexpected sophistication in one of the simplest ears known and a
novel perspective for interpreting bat echolocation calls.
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Jean-Francois Julien
Centre de Genetique Moleculaire
C.N.R.S.
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F-91190 Gif sur Yvette
phone: 33 1 69823226
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