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.

Today's Wine Glasses Are Almost Seven Times Larger Than They Were in 1700

Holiday party season (a.k.a. hangover season) is in full swing. While you likely have no one to blame but yourself for drinking that second (or third) pour at the office soiree, your glassware isn't doing you any favors—especially if you live in the UK. Vino vessels in England are nearly seven times larger today than they were in 1700, according to a new study spotted by Live Science. These findings were recently published in the English medical journal The BMJ.

Researchers at the University of Cambridge measured more than 400 wineglasses from the past three centuries to gauge whether glass size affects how much we drink. They dug deep into the history of parties past, perusing both the collections of the Ashmolean Museum of Art and Archaeology at the University of Oxford and the Royal Household's assemblage of glassware (a new set is commissioned for each monarch). They also scoured a vintage catalog, a modern department store, and eBay for examples.

After measuring these cups, researchers concluded that the average wineglass in 1700 held just 2.2 fluid ounces. For comparison's sake, that's the size of a double shot at a bar. Glasses today hold an average of 15.2 fluid ounces, even though a standard single serving size of wine is just 5 ounces.

BMJ infographic detailing increases in wine glass size from 1700 to 2017
BMJ Publishing group Ltd.

Advances in technology and manufacturing are partly to blame for this increase, as is the wine industry. Marketing campaigns promoted the beverage as it increasingly became more affordable and available for purchase, which in turn prompted aficionados to opt for larger pours. Perhaps not surprisingly, this bigger-is-better mindset was also compounded by American drinking habits: Extra-large wineglasses became popular in the U.S. in the 1990s, prompting overseas manufacturers to follow suit.

Wine consumption in both England and America has risen dramatically since the 1960s [PDF]. Cambridge researchers noted that their study doesn't necessarily prove that the rise of super-sized glassware has led to this increase. But their findings do fit a larger trend: previous studies have found that larger plate size can increase food consumption. This might be because they skew our sense of perception, making us think we're consuming less than we actually are. And in the case of wine, in particular, oversized glasses could also heighten our sensory enjoyment, as they might release more of the drink's aroma.

“We cannot infer that the increase in glass size and the rise in wine consumption in England are causally linked,” the study's authors wrote. “Nor can we infer that reducing glass size would cut drinking. Our observation of increasing size does, however, draw attention to wine glass size as an area to investigate further in the context of population health.”

[h/t Live Science]

Researchers Pore Over the Physics Behind the Layered Latte

The layered latte isn't the most widely known espresso drink on coffee-shop menus, but it is a scientific curiosity. Instead of a traditional latte, where steamed milk is poured into a shot (or several) of espresso, the layered latte is made by pouring the espresso into a glass of hot milk. The result is an Instagram-friendly drink that features a gradient of milky coffee colors from pure white on the bottom to dark brown on the top. The effect is odd enough that Princeton University researchers decided to explore the fluid dynamics that make it happen, as The New York Times reports.

In a new study in Nature Communications, Princeton engineering professor Howard Stone and his team explore just what creates the distinct horizontal layers pattern of layered latte. To find out, they injected warm, dyed water into a tank filled with warm salt water, mimicking the process of pouring low-density espresso into higher-density steamed milk.

Four different images of a latte forming layers over time
Xue et al., Nature Communications (2017)

According to the study, the layered look of the latte forms over the course of minutes, and can last for "tens of minutes, or even several hours" if the drink isn't stirred. When the espresso-like dyed water was injected into the salt brine, the downward jet of the dyed water floated up to the top of the tank, because the buoyant force of the low-density liquid encountering the higher-density brine forced it upward. The layers become more visible when the hot drink cools down.

The New York Times explains it succinctly:

When the liquids try to mix, layered patterns form as gradients in temperature cause a portion of the liquid to heat up, become lighter and rise, while another, denser portion sinks. This gives rise to convection cells that trap mixtures of similar densities within layers.

This structure can withstand gentle movement, such as a light stirring or sipping, and can stay stable for as long as a day or more. The layers don't disappear until the liquids cool down to room temperature.

But before you go trying to experiment with layering your own lattes, know that it can be trickier than the study—which refers to the process as "haphazardly pouring espresso into a glass of warm milk"—makes it sound. You may need to experiment several times with the speed and height of your pour and the ratio of espresso to milk before you get the look just right.

[h/t The New York Times]


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