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See Inside Scientific American Volume 308, Issue 2

Human and Katydid Ears Are Remarkably Similar

Katydid ear structures resemble those of humans
grasshopper, copiphora gorgonesis, katydid grasshopper



Courtesy of Fernando Montealegre-Z University of Lincoln

In a striking example of how two unrelated creatures can evolve similar traits, researchers have discovered that a rain—forest katydid has ears remarkably like those of humans and other mammals-even though its hearing organ is tucked into the crook of its front legs.

The insect, a yellow-orange-faced katydid (Copiphora gorgonensis) from Gorgona Island in Colombia, has ear structures that are similar to the human eardrum and cochlea. As sound waves approach the katydid's legs, they rock a thin membrane akin to a human eardrum. This membrane translates larger movements from air-pressure waves to smaller, more powerful motions in another structure called the cuticle plate. The plate, in turn, creates ripples in a fluid-filled chamber akin to an unfurled human cochlea. Inside this chamber, sensory cells are arranged like a keyboard from high-to low-frequency sensitivity, much like in humans.

C. gorgonensis's exquisitely evolved ear may help it avoid predators such as bats, says sensory biologist Fernando Montealegre-Z, now at the University of Lincoln in England and lead author of the study, which appeared in Science. The finding “is yet another remarkable demonstration of convergent evolution,” says Ronald R. Hoy, a professor of neurobiology at Cornell University, who was not involved in the work.

The efficiency of this minuscule system could inspire engineers to create microsensors based on the katydid’s ear design—for example, for use in hearing aids. Such sensors could be less fragile, smaller and more sensitive, potentially spurring applications we have not thought of yet.

This article was originally published with the title "Bug-Eared."

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