All the better to hear you with, my dear. A chance discovery has revealed that some insects have evolved mammal-like ears, with an analogous three-part structure that includes a fluid-filled vessel similar to the mammalian cochlea.
Fernando Montealegre-Z at the University of Lincoln, UK, and colleagues were studying the vibration of the tympanal membrane – a taut membrane that works like an eardrum – in the foreleg of Copiphora gorgonensis, a species of katydid from the South American rainforest, when they noticed tiny vibrations in the rigid cuticle behind the membrane.
When they dissected the leg behind that membrane, they unexpectedly burst a vessel filled with high-pressure fluid.
The team analysed the fluid to confirm that it was not part of the insect’s circulatory system and concluded instead that it played a cochlea-like role in sound detection. In most insects, sound vibrations transmit directly to neuronal sensors which sit behind the tympanal membrane.
Mammals have evolved tiny bones called ossicles that transfer vibrations from the eardrum to the fluid-filled cochlea. The analogous structure in the katydid is a vibrating plate, exposed to the air on one side and fluid on the other.
Smallest ear
In mammals, the cochlea analyses a sound’s frequency – how high or low it is – and the new structure found by the team appears to do the same job. Spanning only 600 micrometres, it is the smallest known ear of its kind in nature.
The team have since found similar structures in four related katydid species. One is thought to be able to detect frequencies up to 190 kilohertz. By comparison, humans can hear up to about 20 kHz and dogs up to about 60 kHz. “It’s the most ultrasonic animal on the planet,” says Montealegre-Z.
“This is an amazing example of convergent evolution in hearing structures between very distantly related animals,” says Hannah ter Hofstede at the University of Cambridge, who was not involved in the study. “It suggests selection for a common solution to a specific problem.”
Most insects have a calling song in the frequency range that humans find audible, she says, and many appear to rely on changes in the timing of the calls for species recognition, which makes fine-scale resolution of higher frequencies unnecessary. But katydids can have calls with a large variety of frequencies, many of them ultrasonic. “Within a tropical community, there can be more than 100 different species of katydids singing at night,” she says.
It may also help with detecting the echolocation frequencies of predatory bats. “The pressure, evolutionarily speaking, is that a frequency discrimination system will be lifesaving,” says team member Daniel Robert at the University of Bristol, UK.
“You need to tell your mates apart from the bats.”
Mammalian ancestors evolved a different kind of middle ear by adding two elements from the old jaw joint to the columella, resulting in the three-ossicle middle ear that is one of the defining characteristics of mammals (review in Manley 2010).
Among the many orders of insects, hearing is known to exist in only a few: Orthoptera (crickets, grasshoppers, katydids), hom*optera (cicadas), Heteroptera (bugs), Lepidoptera (butterflies and moths), and Diptera (flies). In the Orthoptera, ears are present, and the ability to perceive sounds has been well established.
The mammalian ear is an important example here. Early evolutionary transformation of the cynodont ear presumably was driven by selection for mastication and later also for hearing (Köppl and Manley 2018).
This study supports the view that as people age, their ears get larger, particularly the ear circumference, which increases on average 0.51 mm per year. This enlargement is likely associated with aging changes of collagen.
Tinnitus (pronounced tih-NITE-us or TIN-uh-tus) is the perception of sound that does not have an external source, so other people cannot hear it. Tinnitus is commonly described as a ringing sound, but some people hear other types of sounds, such as roaring or buzzing.
Ear movements are not a useful cue for really anything in humans (or apes), as we've lost our ability to orient our pinnas. We judge a person's attention by their gaze direction. These muscles are part of a system called the vestigial auriculomotor system.
Soon, we learned of the many myths surrounding the number of stomachs in the average Etruscan Shrew. Some believe the species evolved 800 stomachs, though it's difficult to imagine.
In a striking example of how two unrelated creatures can evolve similar traits, researchers have discovered that a rain—forest katydid has ears remarkably like those of humans and other mammals-even though its hearing organ is tucked into the crook of its front legs.
Indeed, insects are capable of nociception, so they can detect and respond to injury in some circ*mstances [3]. While observations of insects' unresponsiveness to injury warrant further research, they ultimately cannot rule out insect pain, particularly in other contexts or in response to different noxious stimuli.
Scientists believe that insects sense vibrations in the air. They might have their vibration sensor in any part of their body: thorax, wing or legs. This organ is used to translate vibrations into nerve impulses that the insect will understand. Most importantly, insects can't hear when you tell them to leave.
Many insects have the ability to hear in a manner quite similar to the way we do it. An insect also has a special receptor called the chordotonal organ, which senses the vibration of the tympanal organ and translates the sound into a nerve impulse.
One possibility is that because mammals are continuous breathers, they isolated their ears from their mouth cavity to prevent breathing sounds from masking external sound.
However, available palaeontological data indicate that the tympanic middle ear most likely evolved in the Triassic period, approximately 100 million years after the transition of the vertebrates from an aquatic to a terrestrial habitat during the Early Carboniferous.
Yet although these ears may differ in some details, they all share certain features: an eardrumlike membrane to capture sound vibrations and small bones--such as the stapes--to transmit the sounds to the inner ear. Based on the fossil record, the earliest known ears of this type date to 200 million years ago or later.
Having three ossicles in the middle ear is one of the defining features of mammals. All reptiles and birds have only one middle ear ossicle, the stapes or columella.
Introduction: My name is Patricia Veum II, I am a vast, combative, smiling, famous, inexpensive, zealous, sparkling person who loves writing and wants to share my knowledge and understanding with you.
We notice you're using an ad blocker
Without advertising income, we can't keep making this site awesome for you.
