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How do scientists know what animals see, hear and feel: how did they find out

'18.04.2023'

Olga Derkach

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Some animals see better than we do, others have a more acute sense of smell, and there are some that can recognize phenomena that we are not able to notice at all, such as magnetic fields. But how do we even know what animals feel? Edition with the BBC sorted everything out.

It is a known fact that some animals have well-developed sense organs.

The sense of smell in dogs is much better than ours, and cats see well in the dark, in which a person cannot do without a flashlight.

Some animals even see things we can't see at all, such as ultraviolet radiation or the Earth's magnetic field.

Stories about the incredible sensory abilities of animals constantly appear in the media. But how do we find out about them? We can't ask a fish or a cat what they see. Or rather, we, of course, can ask, but we will not wait for an answer.

It takes a lot of ingenuity to figure this out. Here are a few ways to imagine what it's like to see through the eyes of a fish or smell through the nose of a dog.

You should start with the simplest: you can observe the animal in its natural conditions. For example, for vultures, large birds of prey that feed on carrion. They are able to spot a carcass from a distance of several kilometers, which is decomposing in the bushes, where it can be well camouflaged. Consequently, vultures are able to recognize the smallest details of objects.

To get more accurate information, you can conduct a behavioral experiment. One of the first such experiments took place at the end of the XNUMXth century. Its author is the English biologist George Romeines.

One day he went for a walk with his dog in London's Regent's Park. Romeines was in a playful mood and decided to test his pet's abilities.

Romeines waited until his dog turned away, then zigzagged away quickly. When the dog noticed that the owner was gone, he immediately began sniffing the ground. Guided only by his sense of smell, he followed in the footsteps of Romeines, exactly repeating his path, and found the owner.

This spontaneous experiment gives a good idea of ​​just how acute a dog's sense of smell is and how useful it can be.

Through further experimentation, George Romeines discovered that dogs could pick up certain scents from a very long distance, even when other, stronger scents were present.

His observation is still regularly cited by forensic experts, including the FBI.

The next step is to study the organs through which animals sense the world. The anatomy of the sense organs can tell a lot about how they function.

For example, the human ear. Inside each of them is the cochlea: a small spiral-shaped organ containing thousands of special nerve receptors that can pick up sounds.

The spiral shape gives us an idea of ​​​​what the principle of the organ is: first of all, the snail recognizes quiet, low sounds well. In 2006, researchers simulated the passage of sound in a spiral and found that low frequencies were amplified. Thanks to the cochlea, a person is able to hear quiet, low-frequency sounds.

insect antennae

The antennae (or antennae) of insects allow them to smell, taste, touch, hear, detect temperature, and feel the breath of air.

In the course of evolution for each of these senses, the corresponding elements appeared on the antennae, they can be seen under a microscope.

Daniel Robert of the University of Bristol (UK) is studying how insects use their antennae to hear. In 2001, together with Martin Gopfert, he studied the antennae of mosquitoes.

With the help of them, mosquitoes pick up audible vibrations. The whiskers also help them identify a member of the opposite sex nearby. Mosquito antennae contain 15 to 16 auditory cells, explains Robert.

Robert and Gopfert aimed a very thin laser beam at a mosquito antenna inside a soundproof capsule. To their surprise, they found that even in complete silence, the antenna vibrated slightly at a frequency of approximately 440-450 Hz.

It turns out that auditory cells are almost always in motion. When a sound wave occurs, the auditory cells begin to move in sync with them, amplifying the sound. As a result, the mosquito hears better.

“Cells add a small pulse of the frequency they need,” says Daniel Robert. “In some cases, this makes it possible to amplify the sound by 10 or even 100 times.”

Robert used a similar microscopic technique to examine the ears of skates located on their forelimbs below the knee.

By taking microCT scans of these tiny ears, Robert and his colleagues found that there was a “lever” system operating inside them that responded to sound-induced vibrations. It also enhances the effect of the sound waves.

On the subject: New York to open a playground where you can study animals

“No one has seen this before,” the researcher says.

When the vibrations pass through the horse's ear, they enter a small, fluid-filled hole that covers the sensory neurons that pick up sound.

Daniel Robert figured this out with a micro-motion detecting laser and a speaker that makes sounds for insects.

“The high frequencies of the sound we broadcast created powerful vibrations at the points of contact, such as our ear curl,” he explains. “The low frequencies traveled further, to other cells below.”

Similar processes take place in the human ear

To learn more, we can resort not only to anatomy, but also to the features of individual cells of the sense organs.

Some deep-sea fish have only rods in their retinas, while humans have both rods and cones in our retinas.

This gives us an idea of ​​how they see. Cones are needed for color vision, so the lack of them in fish indicates their inability to recognize colors.

This is how people learned that dogs' vision is not adapted for the perception of color information.

They have only two types of flasks, while humans have three. As a result, dogs can distinguish yellow and blue shades, but they do not see red and green tones.

With the help of sticks, a person can also see in the twilight.

Deep-sea fish have "huge-sized" sticks, notes Ron Douglas of the University of London. This allows them to capture as much of the available light as possible and see in near darkness.

Smell and taste

The same approach applies to smell and taste.

So, scientists counted the number of olfactory receptors in dog noses. The English hound has more than 200 million of them, while a person has only 5-6 million. Another confirmation that a dog's sense of smell is superior to ours.

Another study in 2006 found that cats do not have taste buds on their tongues that respond to sweets.

It turns out that the representatives of the cat family - from wild lions and tigers to domestic cats - are unable to feel the sweetness of food.

It is not entirely clear why this happened, but felines are staunch meat eaters, and therefore they may not need the ability to recognize sweet tastes.

On the other hand, the olfactory receptors of fruit flies are great at detecting fruity smells, but not much else.

By human standards, their sense of smell can be called limited, but it is well adapted to their needs.

The sensory abilities of animals are not limited to hearing, sight and smell. You can also track how sensory signals travel through the animal's nervous system to its brain.

To do this, scientists use electrophysiological testing. A tiny electrode is placed in the eye or brain of the animal, which picks up the smallest impulses from the sense organs.

One of the key questions is how well the animal sees fast flashes of light. According to Ron Douglas, this helps determine her ability to notice movement.

The human eye can see up to 50 flashes of light per second. If the frequency of flashes increases, it seems to the person that the light is on all the time.

Yes, fluorescent lights flash more than 100 times per second, but we cannot notice this.

Other animals are more sensitive to flickering light. For example, some chickens are able to see about 100 flashes of light per second, so using fluorescent light in a chicken coop is problematic.

"They feel like they're living in a discotheque," explains Douglas. “Obviously it violates animal rights.”

In addition, there is also the brain.

Functional magnetic resonance imaging (fMRI) allows you to find out when a particular part of the brain is activated. To do this, monitor changes in blood circulation and oxygen levels in the blood.

When certain neurons are activated by the sense organs, the body supplies them with oxygenated blood.

This is how we learned that there are certain areas in the dog's brain that process the complex information associated with smells.

A 2015 study found that a dog's brain activity changes depending on whether a dog smells a familiar or unfamiliar human scent.

DNA

And the last step is to study the DNA of the animal.

All features of the animal's sense organs, from their structure to the number of receptors and brain activity, are determined by its genes.

They decide how well the animal sees, hears, smells and tastes.

This means that we can learn a lot about an animal's senses based solely on information about its DNA.

In 2014, researchers scoured the genomes of 13 animal species in an attempt to discover the genes responsible for smell.

African elephants turned out to have more genes related to smell than any other animal studied to date.

We don't know exactly what most of these 2 genes are responsible for, but the number itself suggests that elephant noses are very well adapted.

And one more thing. By that time, people were interested in those sensory abilities of animals that humans also own.

However, some animals can recognize things that we, in principle, are not able to feel. Some beings, for example, are able to see forms of light invisible to the human eye.

For example, many animals see ultraviolet radiation, the wavelength of which is in the range from 10 to 400 nanometers.

We can find out whether an animal sees light at a particular wavelength by checking whether it passes through the lens of its eyes.

The lens of a healthy person blocks ultraviolet radiation, so we cannot see it. However, for many animals, ultraviolet helps to see in the twilight, notes Ron Douglas.

Some surfaces only reflect ultraviolet light, making them invisible to most humans, unlike animals.

For example, the petals of some flowers have reflective stripes of ultraviolet light, so they attract pollinating insects.

“The honey bee sees these marks, which tell it where the nectar is located,” Douglas explains. “For the bees, they are sort of landing lights.”

Bees follow these "nectar markers" by which they collect pollen and can subsequently pollinate other flowers. That is, the system works for both flowers and bees.

Other animals have even stranger sensory abilities, but scientists have found a way to study them too.

For example, we know that migratory birds sense the Earth's magnetic field. The patterns of their flights change in accordance with the movement of the planet's magnetic poles.

How they do it remains a mystery.

According to one hypothesis, there are cells in the eyes of birds that react differently depending on the orientation of the bird relative to the magnetic field - that is, the birds are somehow able to "see" the magnetic field.

Sharks sense electric fields in a similar way. They have special electroreceptors - pores filled with a small amount of gel that conducts an electrical discharge.

When the gel is charged, the hairs in the pores of the hairs move and thus send a signal to the shark's brain.

“Of course, these are very tiny electrical impulses,” explains Ryan Kempster of the University of Western Australia in Perth. However, they help the shark locate a small prey that is out of sight of the predator.

“If the prey cannot be visually tracked, the shark is able to pick up this tiny bioelectrical field and understand where potential prey is,” the researcher adds.

Kempster found that some sharks rely more on electroreception than others.

So, the Australian horned shark has only a few hundred electroreceptors, while the hammerhead shark can have up to three thousand.

Such research sometimes brings unexpected benefits.

The study of the electrical sensitivity of sharks contributes to the development of electrodes to repel these marine predators.

Through them, you can protect swimwear on popular beaches.

“Because sharks are able to pick up very weak electrical fields, they will leave the zone of any unpleasant electrical impulse long before it can do them any harm,” says Ryan Kempster.

And Daniel Robert's research in the field of insect hearing helps in the development of new modifications of hearing aids.

Once Ron Douglas found out that the retina of some deep-sea fish contains chlorophyll. This discovery contributed to the creation of drops for night blindness.

“Of course, this is not what I was looking for in my work, my interest was solely in what animals see,” the scientist explains. “But you never know where your research might take you. Thanks to this, science has taken several steps forward that can help humanity.”

The diversity of animal sense organs is excellent evidence of how the evolution of living organisms has allowed them to interact most fully with the environment.

We can never see the world through the eyes of a condor or hear what a mosquito hears, but we can close our eyes for a moment and try to imagine.

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