A species of roundworm can sense and respond to sound, despite being earless, according to a new study from the University of Michigan Life Sciences Institute.
The findings offer a new biological tool for studying the genetic mechanisms underlying the sense of hearing.
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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,” said Xu, LSI research professor and the study’s senior author. “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.”
Scientists discovered that worms responded to airborne sounds in a certain range. When a tone in the range would play, 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.
The researchers conducted several experiments to ensure the worms were responding to airborne sound waves, and not vibrations on the surface worms were resting on. Rather than ‘feeling’ the vibrations through the sense of touch, Xu believes the worms sense these tones by acting as a sort of whole-body cochlea, the spiraled, fluid-filled cavity in the inner ear of vertebrates.
Read more about the findings here.
The research raises the possibility that other earless animals with a soft body like the roundworm C. elegans—such as flatworms, earthworms and mollusks—might also be able to sense sound.
“Our study shows that we cannot just assume that organisms that lack ears cannot sense sound,” said Xu, who is also a professor of molecular and integrative physiology at the U-M Medical School.
Now that all major senses have been observed in C. elegans, Xu and colleagues plan to delve further into the genetic mechanisms and neurobiology that drive these sensations.
“This opens a whole new field for studying auditory sensation, and mechanosensation as a whole,” he said. “With this new addition of auditory sensation, we have now fully established that all primary senses are found in C. elegans, making them an exceptional model system for studying sensory biology.”