Meet the Flashing, Toxic Disco Clam

You can tell just by looking at Ctenoides ales that this is not the kind of bivalve you'd find in your clam chowder. This reddish-orange mollusk, which makes its home in clusters in the caves and crevices of Indo-Pacific coral reefs, creates flashing light shows so bright that they can be seen without artificial light—hence its common name, the disco clam. Scientists weren't quite sure why, or how, the mollusks flashed; they thought it might be bioluminescence, a chemical reaction that creates light within an animal. But recent research, conducted by University of California, Berkeley graduate student Lindsey Dougherty and scientists from Duke University and the University of Queensland, Brisbane, Australia, shows that there's something a little more complicated going on.

Dougherty used a number of high tech tools—including a transmission electron microscope, a spectrometer, an energy dispersive x-ray spectroscope, and high speed video—to examine the clam mantle lip, and found that the flashes are created not by bioluminescence but by a double layer of specialized tissues. The inside of the clam's lip is packed with spheres of silica that make the tissue reflective to light, like a mirror (or a disco ball!); on the other side of the lip, where no silica balls are present, light is absorbed. When the clams rapidly roll and unroll the tissues—typically at a rate of two times a second—it creates the appearance of flashing. Dougherty could find no other bivalves that have evolved this mechanism; the question is, why do they need it?

Dougherty and her team had a few hypotheses about why the clams flash. Examining the clams' eyes under a microscope showed that, although they have 40 tiny eyes, their eyesight is probably too weak to see displays from other clams, ruling out flashing for the purposes of finding a mate. "We did not find much chemical or visual attraction to one another, and research into their eyes suggests they may not be able to perceive the flashing in one another," Dougherty told LiveScience. But the other two hypotheses had more promise: Flashing to attract prey and repel predators.

To test the prey hypothesis, the scientists released phytoplankton into the tank in their lab. When the clams sensed the prey, their flashing increased. Though some plankton are attracted to light, it's unclear if this is true for the disco clam's prey, and researchers plan to study this question further in the field.

Natural predators of the disco clam include octopuses, mantis shrimp, and some species of snails. But for their first test of the predator hypothesis, scientists used a different kind of foe: A styrofoam lid, which they moved over the clams as if a predator was looming. The clams' flashing went from a rate of 1.5 times a second to 2.5 times a second when they sensed the lid. 

Next, they unleashed an actual predator in the tank. Odontodactylus scyllarus, the peacock or harlequin mantis shrimp, uses its claws—which can deliver 160 pounds of force—to break open clams and other prey. The shrimp attacked the clam a few times, each time retreating from it and, eventually, going into what seemed to be a catatonic state (and then it got a little frisky with the mollusk). "They're very aggressive critters, and to have a clam open and flashing, and the mantis shrimp not attacking, is very weird," Dougherty told LiveScience. "That is very strange behavior [for the mantis shrimp]."

In both experiments, the researchers found high levels of sulfur in the water; Dougherty thinks the clams might be producing an acidic mucus in its tentacles that repels predators. "If you're flashing and saying, 'I'm distasteful; don't eat me,' that's one thing, but you have to sort of back it up," she said.

'Lime Disease' Could Give You a Nasty Rash This Summer

A cold Corona or virgin margarita is best enjoyed by the pool, but watch where you’re squeezing those limes. As Slate illustrates in a new video, there’s a lesser-known “lime disease,” and it can give you a nasty skin rash if you’re not careful.

When lime juice comes into contact with your skin and is then exposed to UV rays, it can cause a chemical reaction that results in phytophotodermatitis. It looks a little like a poison ivy reaction or sun poisoning, and some of the symptoms include redness, blistering, and inflammation. It’s the same reaction caused by a corrosive sap on the giant hogweed, an invasive weed that’s spreading throughout the U.S.

"Lime disease" may sound random, but it’s a lot more common than you might think. Dermatologist Barry D. Goldman tells Slate he sees cases of the skin condition almost daily in the summer. Some people have even reported receiving second-degree burns as a result of the citric acid from lime juice. According to the Mayo Clinic, the chemical that causes phytophotodermatitis can also be found in wild parsnip, wild dill, wild parsley, buttercups, and other citrus fruits.

To play it safe, keep your limes confined to the great indoors or wash your hands with soap after handling the fruit. You can learn more about phytophotodermatitis by checking out Slate’s video below.

[h/t Slate]

Why Eating From a Smaller Plate Might Not Be an Effective Dieting Trick 

It might be time to rewrite the diet books. Israeli psychologists have cast doubt on the widespread belief that eating from smaller plates helps you control food portions and feel fuller, Scientific American reports.

Past studies have shown that this mind trick, called the Delboeuf illusion, influences the amount of food that people eat. In one 2012 study, participants who were given larger bowls ended up eating more soup overall than those given smaller bowls.

However, researchers from Ben-Gurion University in Negev, Israel, concluded in a study published in the journal Appetite that the effectiveness of the illusion depends on how empty your stomach is. The team of scientists studied two groups of participants: one that ate three hours before the experiment, and another that ate one hour prior. When participants were shown images of pizzas on serving trays of varying sizes, the group that hadn’t eaten in several hours was more accurate in assessing the size of pizzas. In other words, the hungrier they were, the less likely they were to be fooled by the different trays.

However, both groups were equally tricked by the illusion when they were asked to estimate the size of non-food objects, such as black circles inside of white circles and hubcaps within tires. Researchers say this demonstrates that motivational factors, like appetite, affects how we perceive food. The findings also dovetail with the results of an earlier study, which concluded that overweight people are less likely to fall for the illusion than people of a normal weight.

So go ahead and get a large plate every now and then. At the very least, it may save you a second trip to the buffet table.

[h/t Scientific American]


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