Roy Caldwell, University of California, Berkeley
Roy Caldwell, University of California, Berkeley

Scientists Crack Mantis Shrimp’s Secret Optic Code

Roy Caldwell, University of California, Berkeley
Roy Caldwell, University of California, Berkeley

Just when you thought mantis shrimp could not get any more awesome, they did. Scientists have learned that mantis shrimp bounce polarized light off their bodies to communicate in super-secret shrimp code. The researchers published their findings in the journal Scientific Reports. 

If you’re new to Mantis Shrimp Club, you’re in for a treat. They look like Happy Meal toys but kill like assassins. And while our eyeballs have just three color receptors, theirs have 16, allowing them to see colors and images accessible to no other animal on earth.

It’s these magnificent peepers that make shrimp code possible. Mantis shrimp can see—and manipulate—polarized light. Other animals can’t, which makes it an ideal way to communicate without attracting attention. 

To find out just how the shrimp do it, scientists collected Haptosquilla trispinosa specimens off the coast of Australia and brought them back to the lab. H. trispinosa do their light-bouncing via little feathery appendages called maxillipeds. Each maxilliped sports a spot of brilliant blue, like the wing of a morpho butterfly. These spots are where the magic happens.

Under a high-powered microscope, the shrimp’s blue spots became fields of thin, reflective cells. Analysis and computer modeling of light across those cells revealed an entirely new way of reflecting light. Most polarizing cells, including those invented by humans, bounce light into a reflective structure. The shrimp cells, on the other hand, unite to scatter light across the spot's surface, an arrangement that yields equally brilliant color and light.

Speaking in a press release, co-author Dr. Nicholas Roberts said the team’s discovery has exciting implications for polarizing technology: “When it comes to developing a new way to make polarizers, nature has come up with optical solutions we haven’t yet thought of.”

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Big Questions
Why Do Dogs Crouch Forward When They’re Playing?
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Whether they're tilting their heads or exposing their bellies for rubs, dogs are experts at looking adorable. But these behaviors do more than elicit squeals from delighted humans; in many cases, they serve important evolutionary functions. A prime example is the "play bow": If you've ever seen a dog crouch forward with its elbows on the ground and its rear end in the air, wagging tail and all, then you know what it is. The position is the ultimate sign of playfulness, which is important for a species that often uses playtime as practice for attacking prey.

The play bow first evolved in canids as a form of communication. When a dog sees another dog it wants to play with, it extends its front paws forward and lifts up its behind as a visual invitation to engage in a friendly play session. Dogs will "bow" in the middle of playtime to show that they're having fun and wish to continue, or when a session has paused to signal they want to pick it back up. Play bows can also be a sort of apology: When the roughhousing gets too rough, a bow says, “I’m sorry I hurt you. Can we keep playing?”

Play between canines often mimics aggression, and starting off in a submissive position is a way for all participating parties to make sure they’re on the same page. It’s easy to see why such a cue would be useful; the more puzzling matter for researchers is why the ancestors of modern dogs evolved to play in the first place. One theory is that play is crucial to the social, cognitive, and physical development of puppies [PDF]. It’s an opportunity for them to interact with their own kind and learn important behaviors, like how to moderate the strength of their bites. Play also requires the animals to react quickly to new circumstances and assess complex actions from other dogs.

Shiba inus playing outside.
Taro the Shiba Inu, Flickr // CC BY 2.0

Another evolutionary explanation is that playtime prepares puppies for the hunting they do later as adults. Watch two puppies play and you’ll see them stalking, biting, and pouncing on one another—all behaviors canines exhibit in the wild when taking down prey.

Of course, it’s also possible that dogs simply play because it’s fun. This is a strong case for why pet dogs continue to play into adulthood. “Devoting a lot of time to play may be less advantageous for a wild species who spends much of its time hunting or foraging for food, searching for mates, or avoiding predators,” Dr. Emma Grigg, an animal behaviorist and co-author of The Science Behind a Happy Dog, tells Mental Floss. “Many domestic dogs are provisioned by humans, and so have more time and energy to devote to play as adults.”

Because play is a lifelong activity for domestic dogs, owners of dogs of all ages have likely seen the play bow in person. Wild canids, like wolves, foxes, and coyotes, tend to reserve this behavior for members of their own species, but pet dogs often break out the bow for their humans—or anyone else who looks like they might be up for a play session. Grigg says, “One of my dogs regularly play bows to her favorite of our cats.”

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Animals
Why Crows Hold Noisy Funerals for Their Fallen Friends
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The next time you hear a murder of crows cackling for no apparent reason, show a little respect: You may have stumbled onto a crow funeral. Crows are among the few animals that exhibit a social response to a dead member of their species. Though their caws may sound like heartbroken cries, such funerals aren't so much about mourning their fallen friends as they are about learning from their mistakes.

In the video below from the PBS series Deep Look, Kaeli Swift, a researcher at the University of Washington's Avian Conservation Lab, investigates this unusual phenomenon firsthand. She familiarized herself with a group of crows in a Seattle park by feeding them peanuts in the same spot for a few days. After the crows got used to her visits, she returned to the site holding a dead, taxidermied crow and wearing a mask and wig to hide her identity. The crows immediately started their ritual by gathering in the trees and crying in her direction. According to Swift, this behavior is a way for crows to observe whatever might have killed the dead bird and learn to avoid the same fate. Flocking into a large, noisy group provides them protection from the threat if it's still around.

She tested her theory by returning to the same spot the next week without her mask or the stuffed crow. She offered the crows peanuts just as she had done before, only this time the birds were skittish and hesitant to take them from her. The idea that crows remember and learn from their funerals was further supported when she returned wearing the mask and wig. Though she didn't have the dead bird with her this time, the crows were still able to recognize her and squawked at her presence. Even birds that weren't at the funeral learned from the other birds' reactions and joined in the ruckus.

Swift was lucky this group of crows wasn't particularly vengeful. Crows have been known to nurse and spread grudges, sometimes dive-bombing people that have harmed one of their own.

[h/t Deep Look]

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