Science news in brief: from a sponge hooked on sugar to dinosaur dental problems

This sponge lives by sipping sugar

Tropical water contains so few nutrients, you can see right through it. And yet coral reefs are oases that support about a quarter of all known species on Earth.

How could that be?

The answer to this paradox, in part, is sugar.

We tend to think the ocean tastes salty. But shaken, stirred and dissolved in seawater are microscopic morsels of sugars and carbs, known as dissolved organic matter. This dissolved substance makes up most of the organic material in the ocean. And it’s especially abundant around coral reefs.

“Imagine all these sugars dissolved into the ocean: if no one can use them, they might as well not be there,” says Michelle Achlatis, a researcher at the California Academy of Sciences.

But then there’s Cliona orientalis.

This filter-feeding sponge lives on coral reefs in the Indian and Pacific oceans, straining tiny plankton to eat as it sits in the water. But its filtering cells also sip sugars from seawater.

It had been known that sponges somehow took in dissolved organic matter, but it remained unclear whether they could do it on their own or needed help from their bacterial symbionts. In a study published in Proceedings of the Royal Society B that used new imaging technology that could see inside the sponge’s filtration cells, Achlatis and her colleagues showed the sponges were capable of taking in these sugars without the bacteria’s help. The group’s study improves understanding of how unusual eating habits help sponges – and coral reef ecosystems – survive on limited nutrients.

Although the team did not look directly at the sponge’s bacteria in this study, they think those symbionts are taking in dissolved organic matter as well, and plan future studies to see if the bacteria do, and if so, how much.

They also plan to use their methods to test other species: while this was the first sponge to reveal its own cells are sugar sippers, it likely won’t be the last.

Cannibalistic dinosaurs went through a lot of teeth

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Plant-eating dinosaurs had to chew lots of tough material to sustain their large bodies, causing them to frequently replace their teeth. But researchers were surprised to discover fossil evidence recently that showed a carnivorous dinosaur – the only known cannibal – replaced its chompers even more frequently than some herbivores. The dinosaur’s propensity for chewing on the bones of its prey might have even contributed to its rapid tooth replacement rate, scientists hypothesise. These results were published in the journal Plos One.

The research centred on several meat-eating dinosaurs, but Majungasaurus crenatissimus was really the star of carnivorous dinosaur dentition. This roughly 20-foot-long apex predator, which lived on what is now Madagascar about 70 million years ago, left behind a particularly plentiful fossil record.

“That’s pretty unheard of,” says Michael D D’Emic, a vertebrate palaeontologist at Adelphi University in Garden City, New York, who led the study.

He and his colleagues also studied fossils of Ceratosaurus and Allosaurus, carnivores that prowled what is now the western United States about 150 million years ago.

D’Emic and his team started by cutting 21 Majungasaurus, Ceratosaurus and Allosaurus teeth into thin slices. They counted fine lines in the dentin, the erstwhile living tissue of the teeth. These lines, each about a fifth the width of a human hair, reflect new layers of tooth tissue that were laid down each day, D’Emic says.

By counting these lines, the researchers built a mathematical model to predict a tooth’s age based on its length.

The scientists next used computed tomography scanning to image tooth-bearing jawbones of the three carnivores. They found multiple teeth on top of one another in tooth sockets, much like nestled ice cream cones.

By taking the difference between the ages of successive stacked teeth, D’Emic and his colleagues calculated the dinosaurs’ tooth replacement rates. Allosaurus and Ceratosaurus both had rates of roughly 100 days, meaning that, on average, a socket would get a fresh tooth about every three months.

But Majungasaurus went through teeth about twice as fast, every 56 days on average, the team found.

But why?

Fossil records from Madagascar have revealed scratches and gouges on the bones of other dinosaurs that match the tooth spacing of Majungasaurus. It’s likely that Majungasaurus crenatissimus was chomping down on the bones of its prey, which included its own species.

“Their teeth were contacting bone a lot,” D’Emic says.

How an icy moon of Saturn got its stripes

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Of the strange and unexplained terrains in our solar system, the south pole of Saturn’s moon Enceladus is among the most perplexing.

Enceladus is an ocean world, with a vast and briny sea tucked beneath its icy crust; this makes it one of the most tantalising places in the solar system to look for life beyond Earth. But unlike other frozen moons, Enceladus constantly erupts. The tiny world blasts salty water into space through cracks in its crystalline shell. These fissures, raked across the moon’s southern pole, are roughly parallel and evenly spaced. Scientists have had a tough time explaining those “tiger stripes”.

“What is going on?” says Doug Hemingway of the Carnegie Institution for Science. “In a way, it’s an obvious question – it’s been in the back of everyone’s mind for a long time.”

Now, Hemingway and his colleagues think they know how the moon got its stripes – and, curiously, why the stripes are found only at the Enceladian south pole. They described their hypothesis in Nature Astronomy.

Previous ideas about the origins of the cracks included massive impacts, hot spots, strike-slip faulting and a migrating icy shell. Hemingway and his colleagues modelled the evolution of the moon’s icy shell, accounting for its thickness, elasticity, strength and temperature, and uncovered a simpler, more comprehensive explanation.

Some time after it formed, they think, Enceladus slowly began to cool. Some of its inner ocean froze, expanded and strained the moon’s icy crust, which was thinner at the poles.

Eventually, the swelling sea fractured the southern crust.

The first fissure to form was 80-mile-long Baghdad, the largest and most prominent. As water began erupting through Baghdad, some of it snowed back to the moon’s surface, piling up near the fracture’s margins. The weight of that accumulating material strained the ice shell, and new cracks – Cairo and Damascus – opened up on either side of Baghdad.

Then Alexandria and “E” opened up.

The tiger stripes’ even spacing is simply a result of the ice’s elasticity and its thickness, which is thinner at the poles and bulkier at the equator.

“It’s kind of a coin toss whether that first fracture happens at the north pole or the south pole,” Hemingway says. But as soon as the crust breaks open, he adds, the swelling ocean’s pressure is relieved “and the other pole will just stay quiet for the rest of time”.

Palaeolithic man’s pal? Or something fiercer?

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An 18,000-year-old puppy buried for centuries in a lump of frozen mud was unveiled by scientists who hope it can help bridge the connection between dogs and wolves.

The puppy, which was male, was discovered 18 months ago, preserved in a layer of permafrost in Siberia’s far eastern reaches, according to Dave Stanton, a research fellow at the Centre for Palaeogenetics in Stockholm and one of the scientists who examined its DNA.

The fur, skeleton, teeth, head, lashes and whiskers of the pup, named Dogor, are still intact, he says. But scientists don’t know whether it is a dog or wolf. Stanton says more DNA research would be conducted in the coming months.

Many scientists say dogs evolved about 15,000 years ago from a species of extinct wolves. Others suggest it could have happened much earlier, perhaps 30,000 years ago or more. These wolves evolved after generations of exposure to humans, were domesticated and became the canine companions we know today.

The puppy, which was found by locals, is being studied at North-Eastern Federal University in Yakutsk, the capital of Yakutia, a sprawling region in eastern Siberia that constitutes 20 per cent of Russia. (The puppy remains were found near Yakutsk.)

Several extinct animals have been found in the thick permafrost, in part because of the melting of ice resulting from climate change.

“It must have frozen quickly before scavengers could get to it,” Stanton says of the puppy. “We also found a lot of samples that were not well preserved. There seems to be natural traps in the landscape where animals are frozen before they decomposed.”

He says the DNA used to date the puppy and figure out its gender was extracted from a rib bone. He says he was not sure if an autopsy was performed to see if its organs, including the heart and liver, were intact.

Why the great auk, once counted by millions, is gone for good

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Not so long ago, the northern seas were full of great auks. Every summer, millions of the two-toned, goose-sized birds would gather at different breeding grounds across the North Atlantic. The flightless birds were easy to capture, and passing sailors loved how they tasted.

“In less than half an hour we filled two boats full of them,” French explorer Jacques Cartier wrote after encountering a throng near Newfoundland in 1534.

Just three centuries later, though, the species had become famous for its scarcity instead. In 1844, members of a small expedition found two of the birds on an Icelandic island, strangled them and crushed their only egg. That was the last confirmed sighting. In this way, the great auk went extinct.

In the past, researchers have speculated that environmental change topped off by human greed took down the great auk.

But new research points the finger more squarely at us. A paper published in eLife that uses genetic analysis from museum specimens to reconstruct great auk population trends, suggests “there was no reason for them to go extinct if they hadn’t been hunted”, says Jessica Thomas, a scientific officer at Swansea University in Wales and lead author of the study.

The birds were gone before we could learn very much about them. Even basic information, like the extent of their breeding season or the sound of their calls, wasn’t well-documented, Thomas says.

The researchers needed a different way to look into the species’ history. So they compared DNA from 41 great auks. They were looking for evidence of species-level vulnerabilities: a shrinking gene pool, for example, or signs that the overall population was fragmenting into smaller groups.

They didn’t find any.

But how did the great auks maintain such high diversity even though they couldn’t fly? By studying data from an unrelated project that uses floating GPS tags to trace sea currents, Thomas’s team found oceanic flows that went straight past a number of former breeding sites, which may have enabled mingling.

Next, the team modelled different extinction scenarios. For instance, assume there were once 2 million great auks in the world. Would the species have gone extinct if people had harvested 9 per cent of the adult birds annually? What about 10 per cent, along with 5 per cent of the eggs?

According to the group’s calculations, only a 2 per cent harvest rate is reliably sustainable. The sailors almost certainly outpaced that, Thomas says.

© New York Times