The Maneater

Caterpillar’s chewing is music to scientists’ ears

MU researchers discover plants can hear themselves being eaten.

Dr. Rex Cocroft and Dr. Heidi Appel, both researchers at the University of Missouri, pose for a portrait in the Tucker Greenhouse on December 3, 2014 in Columbia, Missouri. Recently they found through research that plants will respond to predator noises in their environment.

Dr. Rex Cocroft, professor in the division of biological sciences, has always been captivated by sound. In his younger years, this fascination was rooted in piano.

Today, his passion takes a different form. Now he satisfies his interest for sound with the unfamiliar melody of caterpillars chewing on leaves.

“As a former music major, I am drawn to animal sound,” Cocroft said. “One of things that I like about these odd vibrational sounds that insects send through plants is that they’re very melodic.”

Cocroft’s love of sound made him the perfect partner for the latest project of Dr. Heidi Appel, a senior research scientist in plant sciences. The two partnered over the last four years to research plants and their reaction to sound vibrations produced when herbivores chew on their leaves.

In their research, Appel and Cocroft used precise recording instruments to capture the sounds of caterpillars chewing on leaves and then played the recordings back to plants.

Their findings proved that plants produce a chemical response when they are exposed to sound vibrations caused by caterpillars chewing.

“What people picked up on … is that plants can hear themselves being eaten,” Cocroft said.

Though previous scientific experiments prove that plants can respond to sound vibrations, Appel and Cocroft’s research sought to explore why plants have developed this ability.

The two hypothesized that sound might be another method by which plants can understand that they are under attack by herbivores. Previous research proves that plants have multiple means of understanding attacks, this new study indicates that sound might be the fastest and most accurate warning.

“If you’re a plant, part of the issue is to know whether you’ve been attacked by an herbivore because there are other things that could damage a plant,” Cocroft said.

Sound vibrations are effective because they are a fast method that indicates specific damage by a predator.

“Rex’s work has shown how fast vibrations can travel through plants, and so we think that plant detection of feeding vibrations is probably the fastest signal known so far for the plant to signal danger to the rest of the plant,” Appel said.

Because plants are able to detect when their leaves are being attacked, the plants are able to respond to the attack by releasing a chemical poisonous to their attackers.

“What our research did was provide a reason why plants might have evolved a reason to respond to sound, which is that it can help them respond to their herbivores,” Cocroft said.

Appel said this adaptation helps plants defend themselves. The secretion of chemicals, which are flavorful for humans, are dangerous for caterpillars.

“It’s about better living through chemistry,” Appel said. “For us, the amount of plants we eat are not toxic. But for insects that spend all of their time eating nothing but this plant as a source of nutrition, these chemicals can be toxic and send insects away.”

All plants, Appel said, begin with a baseline level of chemicals that help them function regularly.

When plants perceive additional environmental stimuli, such as the sound of being chewed, they amp up their chemical production to fend off predators.

Appel points to the possibilities their findings present for future research. Appel and Cocroft said they hope to discover if this perception exists in other types of plants.

For now, the two are simply amazed by the nature they’re observing.

“I remember us both being wide eyed and thinking, ‘wow, this is so cool,’” Appel said. “We were like little kids watching a Disney movie.”

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