Natural Sunscreen Explains Mantis Shrimp's Amazing UV Vision
Kay-africa, Wikimedia Commons
Animals and insects see the world in unique ways. From fish, to dogs, to birds to shrimp, super-eyesight allows them to thrive in places others can't.
Dung beetles, for example, have internal compasses that are sensitive to the sun, Marie Dacke of Lund University and her colleagues have determined. In a paper published in the latest Philosophical Transactions of the Royal Society B, she and her team explain that solar cues and skylight help guide where the beetles roll their coveted balls of poop.Video: 5 Incredible Insect Superpowers
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Siberian huskies evolved colorful, almond-shaped eyes to see in low light, desolate northern regions. A quirk of genetics is that an individual dog may have two differently colored eyes. A single eye may also feature two colors. It's known as a "parti" or "split" eye.Photos: Ugliest Dog Contenders
Chameleons can rotate and focus their eyes separately to look at two different objects at the same time, according to the San Diego Zoo. This gives chameleons a full 360-degree view around their body.Photos: Chameleon Colors Act Like a Mood Ring
Ants have vision "superpowers," interactive media designers and artists Chris Woebken and Kenichi Okada believe. Using their ant apparatus, humans can see as ants do by placing microscope antennas on their hands (ants have these on their heads) that transmit a 50-fold magnified view of wherever the person's hand is resting.33 Bizarre New Ant Species Discovered
Imagine if you spent most of the day looking up from below. That is what escolar, a large and mysterious deep-sea fish, do, according to a new study by Eric Warrant of the University of Lund and colleagues. Escolar use this technique to "sit and wait" for prey, hoping something tasty will swim over them.
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Shrimps have some of the most complex visual systems in the animal kingdom. Justin Marshall of the University of Queensland and his team found that some shrimp stare down prey before attacking with a movement that is so swift that it actually boils water in front of the shrimp. (The other temperate water surrounding the shrimp prevents it from cooking itself to death!)
Stewart Butterfield, Flickr
Most animals, including humans, have round pupils, but the eyes of goats (toads, octopi and a few others too) tend to be horizontal and rectangular with rounded corners. This broadens the horizon that they see, enabling them to better spot predators.
Pen Waggener, Flickr
Bird eyes, such as those of the eagle seen here, feature oil droplets located in the front, Doekele Stavenga of the University of Groningen and colleagues have discovered. The droplets serve as "microlenses" that help to filter and direct light.On the Hunt for Bald Eagles
The eyes of certain animals, such as raccoons and cats, glow in the dark. Their eyes have a light-reflecting surface, known as the tapetum lucidum, which makes this possible. Depending on the animal, the glow takes on certain colors. Cats tend to have eyes that glow green. Miniature schnauzer eyes will sometimes glow turquoise, according to Colorado State University ophthalmologist Cynthia Powell.
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Cuttlefish, a type of mollusk, are the transformer visionaries of the animal kingdom. They reshape their entire eyes to adjust to what they see. Humans and many other species, in contrast, usually just reshape their eye lenses to get a better look at something.
Giant squid have the largest eyes in the world, according to the Smithsonian National Museum of Natural History. At up to 10 inches in diameter, the human head-sized eyes help giant squid to see in deep water. It's believed that they can detect a moving sperm whale from 394 feet away.Giant Squid Photos
Fernando Mafra, Fotopedia
We create a mental map of our surroundings in our brain. As Michael Land of the University of Sussex explains, "To interact with objects in the world we need to know where they are, whether they are in our field of view or outside it. Objects in memory have to move in the brain as we move through the world, otherwise they would be not be in the right place."
The bizarre visual system of the colorful mantis shrimp just got weirder: New research finds these animals use a natural sunscreen compound to see ultraviolet light.
Researchers knew that mantis shrimp, marine crustaceans sometimes known to crack aquarium glass with their powerful claws, had a very impressive visual system. The animals can see ultraviolet light, which is light with shorter wavelengths than humans can see. They can also see the orientation, or polarization, of light waves.
But the new study reveals that mantis shrimp have come up with some pretty neat tricks to pull off their impressive visual abilities. They recruit special amino acids that are usually used as a natural sunblock in animal skin to filter the light that reaches their eyes.
"The overall construction of the mantis shrimp's visual system is just so unbelievably ridiculous, so this is just another piece of that tapestry," said study researcher Michael Bok, a doctoral candidate at the University of Maryland, Baltimore County. [Photos: The Amazing Eyes of the Mantis Shrimp]
Mantis shrimp are complicated creatures. They are fierce hunters, killing prey with swift blows from their powerful claws, which can accelerate as fast as a .22-caliber bullet. Some species are monogamous, but all exhibit complex social behavior.
Mantis shrimp vision seems to be a crucial ingredient to the animals' success. Mantis shrimp have 12 photoreceptors, compared with three in humans, and they see more wavelengths of light than humans do.
Weirdly, though, mantis shrimp don't seem to discriminate between colors with as much sensitivity as humans; a study published in January in the journal Science found that their impressive 12-photoreceptor array allows them to process color in the eye instead of in the brain. (In contrast, humans have a fairly simple eye, but lots of visual processing set up in the brain that helps us to see thousands of shades.)
Mantis shrimp photoreceptors are organized in a band in the middle of the eye, with simpler cells around them, Bok told Live Science, and they seem to scan their environment constantly.
"You can envision it as them 'coloring in the world,'" Bok said.
It was these specialized cells that interested Bok and his colleagues. They knew that five or six of a mantis shrimp's photoreceptors were used for seeing ultraviolet light, and they wanted to identify the visual pigments that made up these receptors. An initial molecular analysis of the eye of the species Neogonodactylus oerstedii, however, turned up only two pigments.
A mantis shrimp eye. A center line, called the midband, contains complex photoreceptor cells.Michael Bok
That was a bit of a surprise, Bok said. The researchers figured the mantis shrimp eye must have filters to "sort" wavelengths before they hit the visual pigments, but the scientists didn't know where to look, at first. Because UV wavelengths are invisible to humans, there would be no way to see the UV filters with the naked eye.
Fortunately, the researchers discovered that as the filters in mantis shrimp eyes absorb UV light, they emit a tiny bit of fluorescence, visible to humans.
"We were able to see these very bright, beautiful fluorescing pigments in the eye," Bok said.
The filters are made of something called MAAs, or mycosporine-like amino acids. These amino acids are common in the skin of marine organisms, and are usually used to absorb cell-damaging UV light.
Mantis shrimp, however, have repurposed the MAAs to absorb certain UV wavelengths in the eye. Each different filter removes different portions of the light, meaning that certain wavelengths only hit certain areas of the eye.
"It pretty nicely narrows their sensitivity by removing certain components of the spectrum," Bok said. The filtering thus enables the mantis shrimp to detect multiple wavelengths with only two visual pigments.
"It's a very, very strange system, and it's very alien compared to ours," Bok said.
Bok, who is currently doing fieldwork on the Great Barrier Reef in Australia, said the next goal is to study how mantis shrimp use their unusual visual system. They might use visual information to communicate, to hunt or to avoid predators, he said.
"It's an interesting question," he said. "Why do they need this? What could it possibly be used for?"
Bok and his colleagues reported their findings today (July 3) in the journal Current Biology.