Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Squid studies provide valuable insights into hearing mechanisms

18.10.2010
The ordinary squid, Loligo pealii—best known until now as a kind of floating buffet for just about any fish in the sea—may be on the verge of becoming a scientific superstar, providing clues about the origin and evolution of the sense of hearing.

In a hangar-like research building at the Woods Hole Oceanographic Institution (WHOI), biologist T. Aran Mooney is exploring virtually uncharted waters: Can squid hear? Is their hearing sensitive enough to hear approaching predators? How do squid and other marine species rely on sound to interact, migrate, and communicate? Will the burgeoning cacophony of sound in the ocean disrupt marine life's behavior and threaten their survival?

"The sound in the ocean is increasing…commercial shipping, oil and gas exploration…those make a lot of noise," Mooney says. "And you don't know how that is going to affect the animal unless you know what it hears."

Mooney, a postdoctoral scholar at WHOI, has undertaken seminal investigations into the hearing of this seminal creature in the marine food web. His study is published Friday, Oct. 15, in the Journal of Experimental Biology

"Almost every type of marine organism feeds somehow off the squid," says Mooney. Not just fish, but also many birds, seals, sea lions, and dolphins and toothed whales depend heavily on squid. Whales, according to Mooney, consume some 320 metric tons of squid a year; people eat another 280 metric tons annually.

Mooney says it may be the squid's role as a predator's entrée that holds the key to understanding the importance of hearing among squid and other ocean creatures. This is because predator avoidance is a key pressure for evolving hearing capabilities. If you can hear your predators approaching, you have a better chance of avoiding them. Eventually, he said, a better understanding of how squid hear may shed light on human hearing as well.

Despite their importance in the marine food web, little is known about how well squid hear and whether they rely on hearing to navigate, sense danger, and communicate with each other. Until recently, it wasn't clear that they even hear at all.

It is known now, through the work of Mooney and others, that the squid hearing system has some similarities and some differences compared to human hearing. Squid have a pair of organs called statocysts, balance mechanisms at the base of the brain that contain a tiny grain of calcium, which maintains its position as the animal maneuvers in the water. These serve a function similar to human ear canals.

Each statocyst is a hollow, fluid-filled sac lined with hair cells, like human cochlea. On the outside of the sac, the hair cells are connected to nerves, which lead to the brain. "It's kind of like an inside-out tennis ball," Mooney said, "hairy on the inside, smooth on the outside."

The calcium grain, called a statolith, enables the squid to sense its position in the water, based on which hair cells it's in contact with at a given moment. Normally it rests near the front of the sac, touching some of the hair cells.

When a squid moves quickly—as it does when it flees an approaching predator—the heavy calcium stone lags behind slightly before catching up to the hair cells. "Kind of like your stomach on a roller coaster," Mooney said. "The hair cells are very sensitive and can detect the calcium statolith lagging behind, then catching up."

Structurally, the statocyst "is analogous to our auditory system," said Mooney, who began his hearing research while working on his Ph.D. at the University of Hawaii. The statocyst, he thinks, "is on its way to becoming an ear" like the more familiar ears of vertebrates.

But to what extent does it function as an ear? "One of the obvious questions is, 'Can this acceleration-sensing 'ear' to also detect sounds?' Then, if they can hear sounds 'Do squid hear their predators coming?' " Mooney asked.

To find out if squid have true, functioning "ears," Mooney tests whether the nerves coming from the statocysts send impulses in response to sound. He anesthetizes a squid and attaches an electrode just under the skin near the nerves that extend from the statocysts. He attaches another sensor into the squid's back to get baseline measurements of electrical signals, because that part of the body should not respond to sounds.

He then lowers the squid into a shallow, 3-foot-wide tank. Also in the tank is a speaker that can emit a broad range of sound frequencies—pure tones repeated about 1,000 times for each frequency. He then records the 1,000 responses to each. Averaging those 1,000 responses reduces the natural, random electrical noise in the body yielding the electrical signals, in millivolts, that occur along the nerves after each tone. This hearing test method is similar to those used to checking hearing in human infants.

His preliminary findings indicate that nerve responses showed the squid "actually do hear," he said. "But they only hear up to a certain frequency, about 500 Hz, which is pretty typical of a lot of fish that don't hear very well." Humans hear from about 20-20,000 Hz. Squid also do not detect the very high frequency sounds of dolphin echolocation clicks.

That may help explain why squid are such a prolific food source: They may not always hear well enough to get out of the way of approaching predators. But when Mooney and his post-doc advisor [name?] put the squid in a CT scanner, they found that squid may avoid predators in another way: they are almost the same density as water. That is, when squid were scanned in water, the CT could not image the squid body, illustrating that squid are nearly transparent to sound. This would likely make them very difficult for echolocating predators to detect. So, perhaps, squid could not take the evolutionary leap to adapt ears to detect very high frequencies, but being close in density to water is advantageous for several reasons, including avoiding predators.

Still, its auditory mechanisms have been good enough to make squid successful in an evolutionary sense. What, then, is the main purpose of the squid's hearing system?

Mooney said his work falls under the heading of "sensory biology," the study of how animals use their sensory systems to figure out the world around them. After the initial tests to see how sensitive squid are to sounds and their frequency range, he next studies will be to try to determine how important those abilities are to the animal. Do squid rely on sound to interact, migrate, communicate?

In one set of experiments Mooney will move the speakers to different positions and measure the nerves' response to see if they sense the location of that speaker.

"It's been suggested that a primary evolutionary drive behind hearing is to locate where the sound source is," he said. "If your mother is calling to you, you have to know where your mother is. If there's a predator coming you'd better darn well know where that predator is coming from so that you can get out of the way."

Another question Mooney wants to pursue is how much—if at all, squid are affected by sounds of human origin in the ocean. Loud sounds, whether a sudden explosion or continuous ship traffic, might cause squid to migrate unnaturally just to escape the racket.

Mooney also thinks squid statocysts can tell scientists a lot about how ears originated and evolved.

"Humans, fish, and lots of animals use hair cells to detect sound and movement. Their hair cell structures are similar to squid, but also quite different," said Mooney. "There is probably a basic structure which evolved millions of years ago, but vertebrates and invertebrates have taken quite different evolutionary paths since.

"By learning more about squid hearing and squid hair cells, we might learn what is important in human hearing and human hair cells, or other animals for that matter," he said. "Down the road, squid ears and hair cells might be models for examining human hearing. But that's just speculative right now. We need to learn more about the basic functioning of squid ears first."

Paul Nachtigall, a biologist at the University of Hawaii who advised Mooney on his doctoral research on hearing and echolocation in whales and dolphins, said Mooney's research on squid hearing mechanisms and the ecological uses of hearing in squid are "groundbreaking."

"Aran was launched out of here with great success," said Nachtigall, "and his rocket appears to have reached stage two prior to reaching a stellar orbit."

Mooney's work with squid is funded by The Grass Foundation and a WHOI Independent study award from the Andrew W. Mellon Fund for Innovative Research.

The Woods Hole Oceanographic Institution is a private, independent organization in Falmouth, Mass., dedicated to marine research, engineering, and higher education. Established in 1930 on a recommendation from the National Academy of Sciences, its primary mission is to understand the oceans and their interaction with the Earth as a whole, and to communicate a basic understanding of the oceans' role in the changing global environment.

Media Relations | EurekAlert!
Further information:
http://www.whoi.edu

More articles from Life Sciences:

nachricht What happens in the cell nucleus after fertilization
06.12.2016 | Helmholtz Zentrum München - Deutsches Forschungszentrum für Gesundheit und Umwelt

nachricht Researchers uncover protein-based “cancer signature”
05.12.2016 | Universität Basel

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Significantly more productivity in USP lasers

In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.

Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...

Im Focus: Shape matters when light meets atom

Mapping the interaction of a single atom with a single photon may inform design of quantum devices

Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

Simple processing technique could cut cost of organic PV and wearable electronics

06.12.2016 | Materials Sciences

3-D printed kidney phantoms aid nuclear medicine dosing calibration

06.12.2016 | Medical Engineering

Robot on demand: Mobile machining of aircraft components with high precision

06.12.2016 | Power and Electrical Engineering

VideoLinks
B2B-VideoLinks
More VideoLinks >>>