Caenorhabditis elegans is a unique nematode species that is often used for research. Until now, it was believed that he had a limited range of senses. Thanks to the latest research, it has been confirmed that he can also hear, despite the lack of hearing organs. However, it does it in an original way – sensing sounds through the skin.
Scientists from the laboratory of the Institute of Life Sciences of the University of Michigan have been studying for 15 years Caenorhabditis elegans for the senses. When research began, the nematode was thought to have only three main senses: touch, smell, and taste. Since then, scientists have been able to establish that these animals have the ability to sense light, despite the lack of an organ of sight, as well as the ability to orient their own body when moving (so-called proprioception).
“There was one more basic sense missing – hearing,” said Shawn Xu, a professor at the University and lead author of the study. “But hearing is unlike the other senses that are common to other types of animals.” In fact, it was only discovered in vertebrates and some arthropods. Therefore, the vast majority of invertebrate species are considered sound insensitive, he added.
The researchers found that the nematodes responded to sounds ranging from 100 hertz to 5 kilohertz. This is a wider range than some vertebrates can catch. When a sound was played in this range, animals quickly drifted away from its source, which proves that not only can they hear the sound, but can sense where it is coming from.
They work like a snail
Scientists conducted several experiments to make sure that the animals responded to sound waves in the air, and not to the vibrations of the surface on which they were resting. Instead of ‘feeling’ the vibrations through the sense of touch, Xu believes that nematodes sense these tones, acting like a snail, the spiral, fluid-filled part of a vertebrate’s inner ear.
Caenorhabditis elegans they have two types of auditory sensory neurons that are tightly connected to the skin. When sound waves strike the skin of the worms, they cause it to vibrate, which in turn can cause the fluid inside the worm to vibrate – in exactly the same way that fluid vibrates in the inner ear cochlea. The vibrations activate the auditory neurons associated with the skin of the worms, which then act on nerve impulses.
Since both types of neurons are located in different parts of the nematode’s body, it can detect the source of the sound depending on which neurons have been activated. This sense can help detect and avoid predators that make audible sounds when moving and hunting.
Independent and multiple evolution
These studies have also led to speculation whether other types of animals, such as annelids, flatworms, and molluscs, can perceive sounds.
“Our research shows that we can’t just assume that organisms without ears can’t sense sound,” Xu said.
While the nematode’s sense of hearing shows some similarity to that of the vertebrate auditory system, new research reveals important differences from sensing sounds.
“Based on these differences, which exist down to the molecular level, we believe that the sense of hearing probably evolved independently and repeatedly in different types of animals,” Xu said.
He added that it was clear to scientists that vertebrates and arthropods perceive auditory stimuli differently.
– Now, thanks Caenorhabditis elegans, we found yet another path for this sensory function that points to converging evolution. This is in sharp contrast to the evolution of vision which, according to Charles Darwin, occurred fairly early and probably only once in one common ancestor, he added.
A new field of research
Now that all major senses have been observed u Caenorhabditis elegans, Xu and his colleagues plan to study the genetic and neurobiological mechanisms that drive these experiences.
– This opens up a completely new field for research on the sense of hearing. With this new addition, “auditory sensation”, we have managed to fully establish that all primary senses exist in Caenorhabditis elegans. This makes them a unique model species for studying the biology of the senses, Xu said.
The research results were published last week in the academic journal “Neuron”.
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