Science news in brief: From sharks stabbed by swordfish to dinosaur brains

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<p>Killer fish: why do sharks keep getting stabbed?</p>

Killer fish: why do sharks keep getting stabbed?

Sharks wash up on beaches, stabbed by swordfish

The first victim washed up in September 2016. Police in Valencia, Spain, saw a blue shark dying in the surf along a tiny stretch of beach. They lugged the eight-foot corpse to the yard behind the police station. Then they called Jaime Penades-Suay, who soon suspected foul play.

The shark had what looked like a bit of wood embedded in her head. He pulled. Out slid a broken fragment from a swordfish sword that had lanced straight through her brain.

“I thought it was crazy,” says Penades-Suay, a graduate student at the University of Valencia and a founder of LAMNA, a Spanish consortium that studies sharks.

But since then at least six more sharks have washed up on Mediterranean coasts, each impaled with the same murder weapon and almost always in the head. In the latest example, an adult 15-ft thresher shark washed up in Libya. Inside was a foot of swordfish sword that had broken off near its heart.

Taken together these cases offer what may be preliminary scientific evidence of high-speed, high-stakes underwater duels that have previously been confined to fisherman’s tales.

When sharks die, their bodies typically sink to the bottom of the sea. So a published record of half a dozen stranded sharks with suspiciously precise wounds could indicate that these encounters are common – and that a swordfish sword is sometimes exactly what it sounds like.

“Now at least we have evidence that they might use it really as a weapon, intentionally,” says Patrick Jambura, a graduate student at the University of Vienna.

Most victims of swordfish stabbings in the Mediterranean have been blue or mako sharks. Both of those species prey on young swordfish, suggesting one explanation: maybe juvenile swordfish had felt like their lives were threatened and fought back.

But this time the sword fragment looked as if it had come from an adult swordfish, which typically are not eaten by a thresher shark. Instead, Jambura and his team argue the swordfish might have been taking out an ecological rival.

Penades-Suay doubts competition would be enough of a motive given the risks involved in taking on a big, whip-tailed shark. Instead, he thinks the swordfish might have felt attacked and tried to protect its territory.

 Joshua Sokol

You wouldn’t want to get caught in this arachnid’s web

Spider silk is stronger than steel. It also assembles itself

Pound for pound, spider silk is stronger than steel and tougher than Kevlar. But it doesn’t start out that way.

The silk starts out in a liquid form called dope. But in fractions of a second, this goopy, liquid slurry of proteins is transformed. And it doesn’t just turn into a solid. On their way out, the protein building blocks in silk, called spidroins, fold themselves and interlace, creating a highly organised structure without guidance from any outside force.

“You can really generate materials with unique properties by exploiting this self-assembly process,” says Ali Malay, a structural biologist and biochemist at the Riken Centre for Sustainable Resource Science in Japan.

Malay doesn’t yet have the entire process figured out. But in a paper published in Science Advances, he and his colleagues lay out a new way to tackle the spider silk puzzle, mimicking its orderly exit from the spinneret with chemical tools in the lab.

A crucial part of spinning, the researchers find, requires the spidroins to separate themselves from the watery buffer that swaddles them inside silk glands – a step that hyper-concentrates the proteins. An influx of acid then prompts the proteins to securely interlock.

The metamorphosis spider silk must undergo as it exits an arachnid cannot be overstated, says Anna Rising, a spider silk expert at the Karolinska Institute in Sweden who was not involved in the study. While still in the gland, spidroins have to stay suspended in a liquid form at “really extreme concentrations,” Rising says.

To form the more stable architecture required of solid silk, the spidroins need to link up in chains. As the spidroin slurry is extruded through a labyrinth of increasingly narrow ducts, the spider cells pump acid into the mixture, making the free ends of the barbells stick together.

Katherine J Wu

Catching some waves: who knew whales made such good surfboards?

How suckerfish surf across blue whales without falling off

In 2014, Jeremy Goldbogen, a marine biologist at Stanford University, stuck video cameras on the backs of blue whales, hoping to learn more about their feeding habits. When he retrieved the footage, he realised he had been photobombed. Dozens of Remora australis were treating his research subjects like dance floors.

Remoras – also known as suckerfish or whalesuckers – hitch rides with cetaceans, sharks and other larger creatures of the deep, attaching to them by means of a “sucking disc” that sits on their head like a flat, sticky hat. They then act as a kind of mobile pit crew, eating dead skin, parasites and leftovers off their hosts’ bodies as they’re dragged along upside down.

Many scientists have “looked past remoras to whatever charismatic megafauna they were attached to,” says Brooke Flammang, an assistant professor of biology at the New Jersey Institute of Technology. For a study published in the Journal of Experimental Biology, Flammang, Goldbogen and others investigated how remoras manoeuvre while their whale hosts are on the move.

Flammang, who has been working with remoras for years, was filled with questions by Goldbogen’s footage when she first saw it in 2015. To solve these mysteries, Flammang and her collaborators built a 3D digital model of a blue whale.

In the videos, remoras tended to cluster around the whale’s blowhole and dorsal fin. An analysis of how fluid flows around the whale showed these to be low-drag areas protected from the whoosh of water.

Next, they looked into how the remoras were able to surf between these sheltered spots. This came down to a slice of water located just next to the whale, which flows relatively slowly even if the whale is going fast.

According to the model simulations, the boundary layer between the whale’s blowhole and dorsal fin is thick enough that a remora can fit mostly inside of it.

Another analysis, this time of fluid flow around a remora, suggests that as the fish’s sucking disc skims above the whale’s skin, a low-pressure zone forms between them – potentially helping to keep the fish close.

Cara Giaimo

Musk Oxen like to feast at certain times during the year

How musk oxen make it through arctic nights and never-ending days

In the distant reaches of northeastern Greenland, musk oxen amble across the tundra. As Arctic creatures, they need to gather enough energy to make it through cold, dark winters. So when the bright summers come, they eat as if their lives depend on it – which they do.

Their lives are so extreme, scientists have wondered: do they have circadian clocks?

Most creatures on the planet live in lockstep with the planet’s daily cycle of light and dark. Scientists think 24-hour internal clocks help maximise an organism’s survival by keeping it from, for instance, wasting energy foraging at times of day when food may be hard to find.

However, the long night of Arctic winter and the endless day of its summer are very different from conditions on the rest of the planet. And researchers report in a paper published in Royal Society Open Science that musk ox behaviour does not seem to follow a daily pattern year-round. The most prominent cycles in their behaviour are instead those of alternating grazing and digesting, which repeat every few hours, and sometimes are abandoned when the sun doesn’t set in the summer.

The researchers used GPS collars to track 19 free-roaming musk oxen for up to three years, says Floris van Beest, an Arctic ecologist at Aarhus University in Denmark and an author of the new paper. By keeping track of the animals’ movements, they could tell whether they were eating, resting or moving from one area to another over longer distances. They then looked for patterns.

“We don’t find very strong circadian rhythms,” Van Beest says.

Instead, they went through repeated foraging bouts that lasted less than 12 hours. Rhythms were also very different in the winter than in the summer, with some oxen completely losing their patterns in the sunnier months and eating frequently but more or less at random.

To the researchers’ surprise, whether the musk oxen kept up their rhythmic behaviour during the summer seemed to depend on the quality of food nearby. Those in places with lush foraging didn’t keep up their patterns. This suggests that keeping a rhythm helps maximise the energy musk oxen get from sparse food. But it’s a rhythm that repeats on the scale of hours, rather than daily.

Veronique Greenwood

No brawn and all brains: the Buriolestes were quite small

We’ve rarely seen a dinosaur brain like this before

Some 230 million years ago, in the forests of what humans would eventually call Brazil, a small bipedal dinosaur zipped after its prey. It had a slender head, a long tail and sharp teeth, and it was about the size of a basset hound.

Buriolestes schultzi, as palaeontologists have named the creature, is one of the earliest known relatives of more famous dinosaurs that emerged 100 million years later: the lumbering brachiosaurus, up to 80ft long and weighing up to 80 metric tons; the likewise massive diplodocus; as well as other sauropod dinosaurs. By the time the Jurassic period rolled around and the time of Buriolestes had passed, these quadrupedal cousins had reached tremendous size. They also had tiny brains around the size of a tennis ball.

Buriolestes’ brain was markedly different, say scientists who built a 3D reconstruction of the inside of its skull report in a paper published in the Journal of Anatomy. The brain was larger relative to its body size, and it had structures that were much more like those of predatory animals. The findings suggest that the enormous herbivores of later eras, whose ancestors probably looked a lot like Buriolestes, lost these features as they transitioned to their ponderous new lifestyle.

In 2009, Rodrigo Muller of the Universidade Federal de Santa Maria and his colleagues discovered the first partial Buriolestes fossil in southern Brazil. In 2015, they uncovered another Buriolestes nearby – and this time, to their excitement, the dinosaur’s skull was nearly all there.

They found that one portion of the cerebellum, the floccular lobe, was particularly large in Buriolestes. It’s tiny in the enormous brachiosauruses, diplodocuses and other sauropods that lived later, which suggests that the structure grew less important as they transitioned to eating only plants.

Buriolestes also had small olfactory bulbs, suggesting that smell wasn’t of crucial importance to the little hunter. In later sauropods, these bulbs grew in relative size, which might have helped them smell each other or detect predators.

Most striking, however, was the brain’s large size relative to the rest of the body, Muller says. In many lineages, relative brain size increases over time, he says — but not, apparently, in this case.

“Probably this change is related to the feeding habits changing,” he says. “Carnivorous animals generally need more cognitive capabilities.”

Veronique Greenwood

© The New York Times

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