Bats’ Ear Bone Disappearance Turn Them Into Superb Echolocators for Easier Night Hunting

Bats are known to have a unique ability, called echolocation, to find their next meal and to navigate around their habitats. Through sound, bats could easily get in touch with their food, whether it be nectar on flowers or the blood of cattle. Throughout their travel, bats can also take a small bite from insects on the way. Some bat species also have elevated their echolocation and use it whether the prey is underwater.

Bats and Echolocation

In a new study, experts discovered a new anatomical mystery in bats. According to the authors, their ears could explain some of the mysterious factors to why many bat species have evolved with various expertise in hunting.

University of Chicago evolutionary biology expert and author of the study Zhe Xi Luo said in a Science report that their discovery was a huge revelation over the bats. Luo specializes in the field of mammalian hearing and its origins. The expert added that what they found on the bats is unique from other hearing mammals known.

Many bats rely on their superb hearing senses to visualize the surrounding environment. As they produce their tiny chirps, the bats automatically use their ears to register the terrain around them. The soundwaves produced by the bat's chirps bounce back from the structures, similar to what sonars do in large ships. Initial studies thought that the bat ears were just 'perfect' versions of the common mammalian ears.

In 2015, the concept around the hearing of bats gradually changed. University of Chicago biology expert Benjamin Sulser constructed a 3D image of the bat's inner ear, embedded deep in the animal's skull. The imaging results showed that the common bony tube in mammals, which covers the nerve cells and connected the brain to the ear, is missing from the bat's anatomy.

To ensure that they did everything accordingly, Luo did separate imaging from two related species of the first 3D subject. Results from the computed tomography scanning (CT scan) revealed similar results. Instead of a problem, the missing part of the bat ear was determined to be the solution that the biologists was waiting for over two decades now.

Missing Part of Bat's Ear

Bats are divided into two separate groups. The larger fruit bats do not have the ability to echolocate, while the small bats heavily rely on sound for hunt and travel. In recent studies, today's bats emerged from two distinct groups called Yinpterochiroptera and Yangochiroptera. The first group had larger fruit bats and echolocating insect eater members, while the second group is a collective of the remaining small, sound-based bats. Yangochiroptera bats make up 82 percent of the 1250 global bat population that echolocate.

In 24 of 26 bats that Luo's team scanned, the bony region in the brain-ear portion was missing. The common hearing mammals have their ears equipped with a tube piece that is filled with a fluid-like substance. This part vibrates whenever a sound is registered, allowing the tiny cells inside the tube to transmit the sound directly to the brain.

Luo concluded that the Yangochiroptera bats had heightened hearing skills due to the absence of the common bony nerve in their skull. In their auditory nerves, more neurons could have possibly manifested compared to Yinpterochiroptera bats. Luo added that removing parts of the canal could also add more room for a stronger auditory nerve structure. The study was published in the journal Nature, titled "Evolution of inner ear neuroanatomy of bats and implications for echolocation."

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