Science news in brief: From coral’s true colours to one of the solar system’s most puzzling mysteries

When coral’s colourful show is a sign that it is sick

When certain species of coral flash a shimmering palette of vibrant pinks, reds, blues, purples and yellows, they are not simply showing off. This coral is attempting to recover the algae they cannot live without, according to a study published in the journal Current Biology.

Coral depends on a remarkable symbiotic relationship with algae, which lives inside the organism’s tissue. When the algae-coral partnership is thriving, many coral display a healthy brown hue.

Sometimes, after environmental stress, such as a spike in seawater temperature, the algae dies, or the coral expels it. Without that brownish internal photosynthetic factory pumping out meals for the coral, the underlying skeleton shines through the translucent coral flesh as bleach white, and the coral is at risk of starving to death.

But the scientists found that in order to get the algae back, some species envelop themselves in bright, sometimes fluorescent colours, which mitigate intense light reflections through the coral and create conditions for the light-sensitive algae to return.

“They produce their own sunscreen, these colourful pigments,” says Jorg Wiedenmann, professor of biological oceanography at Southampton University, who led the study. “They do it on a regular basis as a survival technique.”

Some healthy corals display vivid colours, and many experts wonder if the colour bleaching process was just a matter of visibility. Perhaps the brownish algae masks other coral’s pigments. Or, perhaps the coral and algae are competing over blue light rays, and once the algae has gone, the coral flexes its fluorescent muscles under all the extra blue light.

But Wiedenmann says their study determines that the process is actually an optical feedback loop that helps restore the symbiotic relationship.

In the first stage of this loop, the algae are lost and the coral turns bleach white. That causes more light to reach and bounce off the reflective coral skeleton.

Within two or three weeks of the original stress incident, the extra light triggers genes in the coral to manufacture the colour pigments. The more sunlight they take in, the more pigment they produce. The pigments block certain wavelengths of light, making it possible for the algae to safely recolonize the coral.

“The optical feedback loop is a beautiful example of how nature regulates processes,” Wiedenmann says. “The corals are changing their physiological setup and are responding to an environmental cue.”

How line-dried laundry gets that smell

People have written poems about it. It has been imitated by candles and air fresheners. It is the smell of line-dried laundry.

Some atmospheric chemists like that scent, too. In a paper published this year in Environmental Chemistry, researchers examined line-dried towels at the molecular level, to try to pinpoint the source of their specific fragrance.

Silvia Pugliese led the research while she was a master’s student at the University of Copenhagen.

In between their more official thesis work, Pugliese and two labmates, with their adviser Matthew Stanley Johnson, commandeered two little-used areas of the university’s chemistry building – an empty office and a small, fifth-floor balcony – and obtained materials, including ultrapurified water and a set of cotton towels.

Each towel got washed three times in the water, and then hung out: inside the office, on the balcony under a plastic shade or on the balcony in the sun.

When a towel finished drying, the researchers sealed it in a bag for 15 hours. As the towel sat in the bag, they sampled the chemical compounds it released into the air around it. The researchers performed similar sampling on an empty bag, an unwashed towel and the air around the drying sites.

By comparing the experimental towels’ chemical profiles to those controls and to each other, the researchers were able to tease out which compounds popped up only when they hung wet towels in the sun, Pugliese says.

Line-drying uniquely produced a number of aldehydes and ketones: organic molecules our noses might recognise from plants and perfumes. For example, after sunbathing, the towels emitted pentanal, found in cardamom, octanal, which produces citrusy aromas, and nonanal, which smells rose-like.

Why is that? It may have to do with exposure to ozone, an atmospheric chemical that can transform some common chemicals into those aldehydes and ketones.

A more fundamental contribution, she thinks, may come from the sun itself. When exposed to ultraviolet light, certain molecules “get excited” and form highly reactive compounds called radicals, Pugliese says. Those radicals then recombine with other nearby molecules, processes that often lead to the creation of aldehydes as well as ketones.

It is possible that the water on a wet towel gathers a lot of these excitable molecules together, and then works “like a magnifying glass”, concentrating the sunlight and speeding up these reactions, Pugliese says.

Wild cockatoos are just as smart as lab-raised ones

When it comes to cognitive testing, the Goffin’s cockatoos at the University of Veterinary Medicine in Vienna are pros.

Researchers have tested them on toolmaking, shape-matching and other tasks, and found that a cockatoo can learn how to solve a problem from watching another cockatoo do it just once.

Now, researchers in Alice MI Auersperg’s lab, the home of the Austrian cockatoo colony, have created an experimental setup they call an “innovation arena”. It is a new way to test the ability of animals to innovate, and might be used for a variety of species, in principle. They compared the performance of laboratory-raised cockatoos and wild-caught birds to see if the lab-raised birds had acquired an edge by hanging out with humans.

As the researchers report in the journal Scientific Reports, the wild birds are just as smart as the captive birds – but a good deal less interested in bothering with the experiment at all.

The “innovation arena” is a semicircular area with 20 doors, each with a different task behind it to solve for a food reward. The bird might have to push a platform down or a lever sideways. The researchers set up a kind of competition between the lab-raised team in Vienna and the temporarily-captive cockatoos at a field station lab in Indonesia.

The Vienna birds, familiar with experiments and their rewards, dove right in when placed at the starting point.

“They very quickly approach the tasks and wander around and try to open the boxes and get out the rewards,” says Theresa Rossler, a researcher.

But they did not always follow the game plan. Sometimes the birds, both lab-raised and wild, “opened the wire task in several instances by removing the window hinges (which were closer to the reward) instead of unbending the wire”, the researchers write.

The big difference between the two groups is in their interest in doing the tests at all. The researchers classified 10 of 11 lab birds as motivated, meaning they began right away to open doors and look for food. Only three of the eight wild birds were motivated.

But the motivated birds – both wild-caught and lab-raised – performed at the same level in solving the tasks.

Rossler says that if the wild birds “decide they want to interact with the apparatus, they are just as skilful problem solvers”.

Long limbs helped propel T Rex up the dinosaur food chain

Surviving in the Cretaceous was not a sprint, it was a marathon. And Tyrannosaurus rex was built to amble for hours, new research reveals. That attribute might have helped propel the carnivore to the top of the food chain, researchers suggest.

A study published last month in PLOS One shows that some dinosaurs were particularly efficient walkers because of their long hind limbs. Thanks to their lanky legs, T rex did not need to eat as much as its brethren, and could therefore get away with hunting less frequently, the team concludes.

In 1976, Robert McNeill Alexander, a British zoologist, proposed that a dinosaur’s maximum running speed depended on its stride length and hip height. But that idea has been revised over time.

In recent years, scientists have realised that long legs will only get you so far – body mass also plays a role.

“Physics won’t let you go any faster” once you get too heavy, says Alexander Dececchi, a paleontologist at Mount Marty College in South Dakota. “Your muscles can’t get you to accelerate fast enough.”

To more accurately estimate dinosaur running speeds, Dececchi and his colleagues amassed measurements of hind limbs and published body mass estimates for 34 dinosaur specimens. For each of the specimens, Dececchi and his collaborators compared calculations of running speed.

The researchers determined that dinosaurs weighing less than a few hundred pounds were actually faster according to the calculations that used their body mass compared with the calculations that did not. In other words, smaller dinosaurs were not slowed by their heft.

But the situation changed for animals larger than about 2,000 pounds – those dinosaurs moved considerably slower, according to the equations that included their mass compared with those that just included stride length and hip height. For behemoths like Tyrannosaurus, that difference was significant: 18mph versus 45mph.

That schism left Dececchi and his colleagues wondering about the evolutionary advantage of lanky limbs for a massive dinosaur. “Their legs are longer than would help them for speed,” Dececchi says. Maybe those limbs allowed the animals to amble more efficiently, the team hypothesise.

Dececchi and his collaborators analysed groups of dinosaurs with similar masses but different leg lengths. For each animal, they estimated how much energy it would expend to move at a slow walk. They found that Tyrannosaurus used between 1 per cent and 35 per cent less energy than other related dinosaurs.

Jupiter’s biggest moons started as tiny grains of hail

Konstantin Batygin did not set out to solve one of the solar system’s most puzzling mysteries when he went for a run up a hill in Nice, France. Batygin, a researcher at the California Institute of Technology, best known for his contributions to the search for the solar system’s missing “Planet Nine”, spotted a beer bottle. At a steep, 20-degree grade, he wondered why it was not rolling down the hill.

He realised there was a breeze at his back holding the bottle in place. Then he had a thought that would only pop into the mind of a theoretical astrophysicist: “Oh! This is how Europa formed.”

Europa is one of Jupiter’s four large Galilean moons. And in a paper published in the Astrophysical Journal, Batygin and a co-author, Alessandro Morbidelli, a planetary scientist at the Cote d’Azur Observatory in France, present a theory explaining how some moons form around gas giants like Jupiter and Saturn, suggesting that millimetre-sized grains of hail produced during the solar system’s formation became trapped around these massive worlds, taking shape into the moons we know today.

Batygin and Morbidelli say earlier theories explain only a part of how the solar system’s many objects formed. They set out to present the rest of the story with equations explaining how a new planet transitions from being surrounded by its disk of matter, to creating satellite building blocks, to the formation of moons like Europa.

When Batygin and Morbidelli ran computer simulations of their proposed theory, they found that they had accidentally recreated Jupiter’s small innermost moons as well as the four Galilean satellites, much as we see them today.

The equations amount to a recipe for how to make a moon. It starts with a mix of hydrogen and helium gas raining down onto Jupiter from above. Some of the gas gets swept out and away, spreading viscously as it goes into orbit around Jupiter.

At this point in Jupiter’s formation, the only solid particles that orbited it were smaller than one millimetre across. Because this dust is very small – tiny grains about two parts ice to one part rock – it can couple itself to the gas washing away from Jupiter.

As this material builds up over the course of about a million years, Batygin says, it eventually reaches a mass that approximately matches Io, Europa, Ganymede and Callisto today.

© New York Times