A species of roundworm that is widely used in biological research can sense and respond to sound, despite having no ear-like organs, according to a new study from the University of Michigan Life Sciences Institute (LSI).
The findings, published on September 22 in the journal Neuron, offer a new biological tool for studying the genetic mechanisms underlying the sense of hearing.
Researchers in the lab of Shawn Xu at the Life Sciences Institute have been using Caenorhabditis elegans to study sensory biology for more than 15 years. When his lab began this work, these millimeter-long worms were thought to have only three main senses: touch, smell and taste.
Xu's lab has since established that worms have the ability to sense light, despite having no eyes, as well as the ability to sense their own body posture during movement (also known as the sense of proprioception).
"There was just one more primary sense missing -- auditory sensation, or hearing. But hearing is unlike other senses, which are found widely across other animal phyla. It's really only been discovered in vertebrates and some arthropods. And the vast majority of invertebrate species are thus believed to be sound insensitive," said Xu, LSI research professor and the study's senior author.
"We proved that worms responded to airborne sounds in the range of 100 hertz to 5 kilohertz -- a range broader than some vertebrates can sense. When a tone in that range was played, worms quickly moved away from the source of the sound, demonstrating that they not only hear the tone but sense where it's coming from," he explained.
The researchers conducted several experiments to ensure the worms were responding to airborne sound waves. They found that worms have two types of auditory sensory neurons that are tightly connected to the worms' skin. When sound waves bump into the worms' skin, they vibrate it.