Researchers at University of Michigan Life Sciences Institute have determined that even though the roundworms lack ear like organs, still they are able to comprehend sound.
Shawn Xu’s sensory biology lab at the Life Sciences Institute have been using Caenorhabditis elegans – transparent nematode about 3 mm in length – to study the sensory mechanism for over 15 years. Initially, however, it was thought that these roundworms were capable of exhibiting only three main senses: touch, smell and taste.
Xu’s lab has established that worms are not only capable of sensing light, even though they do not have eyes but they also have a controlled sense of proprioception.
Dr. Xu, the study’s senior author said that until now, only vertebrates and some arthropods have exhibited the hearing ability. And the vast majority of invertebrate species – insects, spiders, worms, crabs, lobsters, squids, clams and coral – are thus believed to be sound insensitive.
The scientists, on the contrary, discovered that worms do acknowledge sounds that fall in the range of 100 hertz to 5 kilohertz. When they were exposed to sound waves of the mentioned frequency, worms tend to slide away from the source of sound. Thus, proving that they are not only capable of “hearing” the sound but can sense where its coming from.
Researchers iterated the experiments several times to make sure that the worms were reacting to the airborne sounds and not absorbing vibrations from the surface they are resting on.
Pathway for hearing function
To decipher the sense of hearing, Xu believes that the worms entire body acts as a cochlea.
Human cochlea is a tiny coiled structure in the inner ear that looks like snail shell. Its internal structure consists of three fluid filled canals that run parallel to each other. Waves travel through the fluid due to the depression by ossicles (three minuscule bones in either middle ear) cause different frequencies of sound, which are then forwarded as neural activity sent to the brain.
The worms’ skin consists of two types of auditory sensory neurons tightly coupled together. When sound waves hit the worm’s skin, it transmits the vibration into the adjacent fluid. The mode of transduction is similar to the fluid vibrates within cochlea. External vibrations enable the auditory neurons on skin, which eventually renders into a nerve impulse.
The (two types of) neurons are present throughout the worm’s body, and it helps to decipher as well as evade their predators since many produce sounds when hunting.
The discovery has opened up a new paradigm. Researchers now believe that other earless with soft body animals might also sense sound in the similar manner. Now, it’s very difficult to conclude that organisms that lack ears cannot sense sound, added Dr. Xu.
Auditory system in similar animals like flatworms, earthworms and mollusks may not require an ear to sense hearing but their auditory sensory neurons could replicate the hearing function.
Additionally, the study sheds light on how the auditory system works differently in vertebrates and arthropods like insects, myriapods, arachnids and crustaceans.
The team is looking forward to take their research to the next level by delving into genetic mechanisms and neurobiology that drive these sensations.