Nav: Home

The evolutionary puzzle of the mammalian ear

May 27, 2020

The vertebrate ear is a remarkable structure. Tightly encapsulated within the densest bone of the skeleton, it comprises the smallest elements of the vertebrate skeleton (auditory ossicles) and gives rise to several different senses: balance, posture control, gaze stabilization, and hearing. Nowhere else in the vertebrate skeleton are different functional units packed so close together and jointly embedded in its skeletal environment, which also hampers the independent evolution of the ear components.

Even the growth pattern of the ear deviates from that of the remaining skeleton: In humans and other mammals, the inner and middle ears achieve their final size already before or early after birth, which further challenges evolutionary change because postnatal development substantially contributes to anatomical differences between many mammals otherwise.

All this makes it puzzling how mammals, as a predominantly nocturnal group reliant on hearing, were able to occupy such a vast diversity of environments in the aquatic, terrestrial, subterranean, and aerial realms that require an amazing disparity not only in hearing abilities, but also in locomotion and posture. How could the different, tightly connected parts of the ear adapt independently to these diverse functional and environmental regimes?

A group of researchers around Philipp Mitteroecker from the University of Vienna proposed a new explanation for this evolutionary puzzle. Despite its similar function, the ear is composed of different bones in mammals, birds, and reptiles. In birds and reptiles, the lower jaw and its joint are composed of multiple bones, and they have a single auditory ossicle that transmits the sound. Extant mammals, by contrast, have three ossicles (malleus, incus, stapes) and one ectotympanic bone, supporting the tympanic membrane, all of which are separate from the jaw. This evolutionary transformation of the primary jaw joint into the mammalian ear ossicles is one of the most iconic transitions in vertebrate evolution, but it is not clear why this complex transition has happened.

The Austrian research team proposed that this substantial evolutionary change of mammalian ear anatomy has - in addition to any direct enhancements of mastication and hearing - also increased the "evolvability" (capacity for adaptive evolution) of the ear and its associated sensory functions. The incorporation of the bones of the primary jaw joint into the ear has considerably increased the genetic, regulatory, and developmental complexity of the mammalian ear. This increase in the number of genetic and developmental factors, in turn, has increased the evolutionary degrees of freedom for an independent adaptation of the different functional units of the ear: the number of genetic and developmental "knobs" for natural selection to turn.

They suggest that despite the tight spatial entanglement of functional ear components, the increased evolvability of the mammalian ear may have contributed to the evolutionary success and adaptive diversification of mammals in the vast diversity of ecological and behavioral niches observable today. In their article, they show that mammals, as compared to birds, were indeed able to evolve a much wider morphological and functional diversity, including numerous evolutionary "novelties", even though birds are more diverse in species number than mammals.
-end-
Publication in Evolutionary Biology
Anne Le Maître, Nicole D.S. Grunstra, Cathrin Pfaff, Philipp Mitteroecker
"Evolution of the mammalian ear: An evolvability hypothesis"

University of Vienna

Related Hearing Articles:

Two molecular handshakes for hearing
Scientists have mapped and simulated those filaments at the atomic level, a discovery that shed lights on how the inner ear works and that could help researchers learn more about how and why people lose the ability to hear.
Proof-of-concept for a new ultra-low-cost hearing aid for age-related hearing loss
A new ultra-affordable and accessible hearing aid made from open-source electronics could soon be available worldwide, according to a study published September 23, 2020 in the open-access journal PLOS ONE by Soham Sinha from the Georgia Institute of Technology, Georgia, US, and colleagues.
Ultra-low-cost hearing aid could address age-related hearing loss worldwide
Using a device that could be built with a dollar's worth of open-source parts and a 3D-printed case, researchers want to help the hundreds of millions of older people worldwide who can't afford existing hearing aids to address their age-related hearing loss.
A promise to restore hearing
For the first time, researchers have used base editing to restore partial hearing to mice with a recessive mutation in the gene TMC1 that causes complete deafness, the first successful example of genome editing to fix a recessive disease-causing mutation.
Surprising hearing talents in cormorants
The great cormorant has more sensitive hearing under water than in air.
Veterinarians: Dogs, too, can experience hearing loss
Just like humans, dogs are sometimes born with impaired hearing or experience hearing loss as a result of disease, inflammation, aging or exposure to noise.
Older people who use hearing aids still report hearing challenges
A high proportion of older people with hearing aids, especially those with lower incomes, report having trouble hearing and difficulty accessing hearing care services, according to a study from researchers at Johns Hopkins Bloomberg School of Public Health.
Hearing class
New study finds that the class of neurons responsible for transmitting information from the inner ear to the brain is composed of three molecularly distinct subtypes.
Hearing tests on wild whales
Scientists published the first hearing tests on a wild population of healthy marine mammals.
Genes critical for hearing identified
Fifty-two previously unidentified genes that are critical for hearing have been found by testing over 3,000 mouse genes.
More Hearing News and Hearing Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Listen Again: The Power Of Spaces
How do spaces shape the human experience? In what ways do our rooms, homes, and buildings give us meaning and purpose? This hour, TED speakers explore the power of the spaces we make and inhabit. Guests include architect Michael Murphy, musician David Byrne, artist Es Devlin, and architect Siamak Hariri.
Now Playing: Science for the People

#576 Science Communication in Creative Places
When you think of science communication, you might think of TED talks or museum talks or video talks, or... people giving lectures. It's a lot of people talking. But there's more to sci comm than that. This week host Bethany Brookshire talks to three people who have looked at science communication in places you might not expect it. We'll speak with Mauna Dasari, a graduate student at Notre Dame, about making mammals into a March Madness match. We'll talk with Sarah Garner, director of the Pathologists Assistant Program at Tulane University School of Medicine, who takes pathology instruction out of...
Now Playing: Radiolab

What If?
There's plenty of speculation about what Donald Trump might do in the wake of the election. Would he dispute the results if he loses? Would he simply refuse to leave office, or even try to use the military to maintain control? Last summer, Rosa Brooks got together a team of experts and political operatives from both sides of the aisle to ask a slightly different question. Rather than arguing about whether he'd do those things, they dug into what exactly would happen if he did. Part war game part choose your own adventure, Rosa's Transition Integrity Project doesn't give us any predictions, and it isn't a referendum on Trump. Instead, it's a deeply illuminating stress test on our laws, our institutions, and on the commitment to democracy written into the constitution. This episode was reported by Bethel Habte, with help from Tracie Hunte, and produced by Bethel Habte. Jeremy Bloom provided original music. Support Radiolab by becoming a member today at Radiolab.org/donate.     You can read The Transition Integrity Project's report here.