50m-year-old cricket fossils give clues to insect hearing

January 4th, 2012 - 3:29 pm ICT by IANS  

Washington, Jan 4 (IANS) Fifty million year-old cricket and katydid fossils have thrown up significant clues about how insect hearing evolved.

Insects hear with help of unusual ears. Grasshoppers have ears on their abdomens. Lacewings have ears on their wings. The ears of the tachinid fly are tucked under the chin.

“Insects have ears on pretty much every part of their body except on their head proper,” said co-author Roy Plotnick of the University of Illinois at Chicago.

Insects have evolved ears at least 17 times in different lineages. Plotnick and co-author Dena Smith of the University of Colorado, Boulder are trying to figure out when different insects got their ears, and whether predators may have played a role.

Modern insects use their ears to tune in to one another’s chirps, trills and peeps. Think of the chorus of crickets, or the love songs of cicadas.

But many species can also pick up sounds beyond the range of human hearing, such as the high-pitched sonar of night-hunting bats.

Insects that evolved such supersensitive hearing would have had a crucial survival advantage, scientists say.

“The big evolutionary trigger for the appearance of hearing in many insects is thought to be the appearance of bats,” Plotnick said.

“Prior to the evolution of bats, we would expect to find ears in relatively few insects, but after that we should see ears in more insect groups,” he explained.

Plotnick and Smith turned to remarkably well-preserved fossils from a series of lake deposits in Wyoming, Utah and Colorado known as the Green River Formation, where some of the earliest bats are found.

Roughly 50 million years ago, fine-grained sediment covered and buried the animals that lived there and managed to preserve them in exquisite detail.

Researchers examined fossils from a Green River site in Colorado, focusing on crickets and katydids, which have ears on their front legs, just below their knees.

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