Natures wonders: insect ears are like ours (Introduction)

by David Turell , Saturday, December 01, 2018, 01:40 (2183 days ago) @ David Turell

More evidence of convergence:

https://www.scientificamerican.com/article/awesome-ears-the-weird-world-of-insect-heari...

"The renown of this katydid rests not on its looks, though, but on its hearing. Montealegre-Z’s meticulous studies of the magnificent insect revealed that it has ears uncannily like ours, with entomological versions of eardrums, ossicles and cochleas to help it pick up and analyze sounds.

"Katydids—there are thousands of species—have the smallest ears of any animal, one on each front leg just below the “knee.” But their small size and seemingly strange location belie the sophisticated structure and impressive capabilities of these organs: to detect the ultrasonic clicks of hunting bats, pick out the signature songs of prospective mates, and home in on dinner. One Australian katydid has capitalized on its auditory prowess to capture prey in a very devious way: It lures male cicadas within striking distance by mimicking the female part of the cicada mating duet—a trick requiring it to recognize complex patterns of sound and precisely when to chip in.

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"When insects first appeared some 400 million years ago, they were deaf, Göpfert tells me. These ancestral insects went on to diversify into more than 900,000 species, and while most remain as deaf as their ancestors, some gained the means to hear. Of the 30 major insect orders, nine (at last count) include some that hear, and hearing has evolved more than once in some orders—at least six times among butterflies and moths. The 350,000 species of that most dazzlingly diverse group, the beetles, are almost all deaf, yet the few that have ears acquired them through two separate lines of evolution. All told, insect ears arose more than 20 separate times, a sure-fire recipe for variety.

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"Katydid ears, as so neatly demonstrated by Montealegre-Z and his colleagues, are unique both in their complexity and their similarity to a mammal’s. Using a micro-CT scanner, the scientists reconstructed the insect’s entire hearing system, discovering two previously unknown organs in the process. The first is a small, hard plate behind the eardrums; the second, a fluid-filled tube containing a line of sensory cells. Through painstaking investigation that included shining lasers at the eardrum and recording the light bouncing back, the team showed that the small plate transmits vibrations in the insect’s eardrum to the fluid in the tube—the same role played by the bones in our middle ear. The signal then travels in a wave along the tube and over sensory cells tuned to different frequencies—making this organ a miniature, uncoiled version of our own, snail-shaped cochlea.

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"Katydids solved the problem (again, in a unique way) by enlarging a breathing tube that runs from a pore in the side of the chest to the knee; sound reaches the eardrums both from outside the body and from the inside via the tube. Montealegre-Z and his colleagues showed that sound travels this inner, back route more slowly—so each sound hits the eardrum twice, but at slightly different times, dramatically improving the insect’s ability to locate the source.

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"In modern insects, one of the primary functions of ears is to hear the approach of a predator in time to take action and avoid it. For night-flying insects, the greatest threat comes from insectivorous bats that detect and track prey with ultrasonic sonar, and so their hearing is tuned to the frequencies of the bats’ echolocating clicks. The insects then respond with characteristic moves to escape the sonar beam: sharp turns, loop-the loops, air-to-ground power dives. Certain tiger moths even jam the bat sonar with clicks of their own. Experiments have shown that bat-detecting ears dramatically improve an insect’s prospects of surviving attack: In one study, mantises escaped 76 percent of bat attacks, but that number fell to 34 percent when they were deafened."

Comment: An amazing example of convergence. I think God sets patterns which he uses over and over creating this parallelacism of results. There is lots more of interest in this giant article about insect hearing and how sound receptors are placed in all sorts of spots on the body.