Researchers at the University of Maryland discovered that lizards use a mechanism normally associated with balance to detect vibrations, providing new insights into how the animals perceive auditory and tactile stimuli. Biologists at the University of Maryland have discovered a previously unknown ability in lizards, and it turns what we thought we knew about animal hearing on its head.

In a new study published Current Biology October 4, 2024 Researchers have discovered that lizards use the pouch, a part of the inner ear traditionally associated with balance and body position, to detect low-frequency vibrations. According to the researchers, this special “sixth sense” also plays an additional role in geckos’ normal hearing and how they perceive the world around them. The team believes that this previously unknown hearing mechanism may also be present in other reptile species, challenging current ideas about how animal sensory systems developed and differentiated over time.

A new role of the pouch in the auditory apparatus of geckos

“The ear hears air sound as we know it. But this ancient internal pathway, normally associated with balance, helps lizards detect vibrations traveling across land or water,” said study co-author Kathryn Carr, UMD Distinguished Professor of Biology. “This pathway is present in amphibians and fish, and has now been proven to be conserved in lizards. Our findings shed light on how the auditory system evolved from that seen in fish to that seen in land animals, including humans.”

The pouch can detect weak vibrations in the range of 50 to 200 Hz; This is a spectrum well below what geckos can normally hear with their ears. The researchers say this suggests that the sac serves a separate but complementary function from the gecko’s normal auditory system. Although geckos can hear sounds in the air, many other reptiles cannot. Discovering the pouch’s role in lizards’ hearing could lead to a better understanding of the communication and behavior of other animals previously thought to have limited hearing abilities, says the study’s lead author, postdoctoral researcher and former UMD graduate student Dawei Han.

Broader implications for reptiles and evolution

“Many snakes and lizards were thought to be ‘mute’ or ‘deaf’ because they were unable to make sounds or hear sounds well,” Hahn said. he explained. “But it turns out that they can potentially communicate through vibration signals using this sensory pathway, which is really changing the way scientists think about animal perception in general.”

The existence of this common sensory pathway in modern reptiles opens a unique window into the evolutionary history of vertebrate sensory systems; This suggests that the transition from aquatic to terrestrial environments likely involves more complex and gradual changes in auditory mechanisms than previously thought.

Although these discoveries are not directly related to how humans hear, researchers believe there is always more to it than meets the eye, or in this case, hearing.

“Imagine being at a live rock concert,” Carr said. “It’s so loud you can feel your whole head and body vibrating in the sound field. Music is not just heard, it is felt. “This feeling suggests that the human vestibular system may be stimulated during loud concerts, meaning that our hearing and sense of balance may be closely related.”

Carr and Hahn hope their findings will lead to further research on hearing in mammals, especially in the context of this sensory pathway. They believe that the established connection between hearing and balance opens new avenues of research, including the link between hearing and balance disorders in humans.

“The implications of this research go beyond the reptile world,” Hahn said. “As we uncover these hidden mechanisms, we gain a richer and more detailed picture of how animals perceive and interact with their environment, and perhaps new insights into our own sensory experience.”