Science news in brief: From head-chewing parasitic wasps to palaeolithic bone marrow

This wasp is an equal-opportunity head-chewer

To deposit its eggs, the parasitic oak gall wasp pierces a leaf or stem with its ovipositor, a tubelike organ. The plant swells, forming tumorlike growths called galls. These serve as nursery domes, or “crypts”. Within each crypt, a wasp egg develops until it is large enough to chew a hole into the gall’s skin and emerge an adult. That is, unless the crypt-keeper wasp – Euderus set, a parasite in its own right – arrives.

The wasp locates smooth, dome-shaped galls created by the other wasps. Then, puncturing the gall, it injects its eggs beside or inside the young oak gall wasp, Bassettia pallida. As both eggs develop inside the crypt, the baby crypt-keeper feeds off the body of baby Bassettia.

Just as the Bassettia begin chewing an escape hatch into the gall skin, Euderus stops it. Now the unfinished hole is too small to allow exit. Bassettia’s head becomes caught, and a few days later, Euderus will crawl into the head and chew its way out, the victor: a parasite’s parasite. A study led by Scott Egan, at Rice University, indicates that the crypt-keeper used many different species of hosts, and all the hosts had one key thing in common: the galls they occupied were small, smooth, non-woody, lacking fuzz or sharp spines – defenceless.

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Pondering a mollusc with acrobatic skills

Why did the chiton roll into a ball? “To get to the other side,” says Julia Sigwart, an evolutionary biologist at Queens University Belfast in Northern Ireland.

About 500 million years ago, a couple of species of now-extinct trilobites became the first animals to roll themselves into a ball for protection. The trilobite’s living doppelgänger is the chiton. This marine mollusc’s plated shell drapes over a soft body and mucousy foot, giving it the appearance of a flattened piece of shrimp nigiri.

Like trilobites, three-banded armadillos, pill bugs, hedgehogs and other animals, the chiton can roll itself into a ball. Many scientists had assumed this acrobatic manoeuvre, known as conglobation, defends the animals, most of which are smaller than an inch or two, against predators. But Sigwart, who studies chitons, never really bought that explanation: if a predator can swallow you whole, she reasoned, rolling into a Tic Tac probably would not save you.

In a series of lab experiments, Sigwart showed that rolling into balls has more to do with helping chitons get to places where they can reattach after losing their footing. She hopes that these findings, published in Biology Letters, add evidence to a novel argument: that chitons are capable of making decisions.

Chitons do sometimes roll defensively, for instance, if they perceive a need to protect their soft bodies when poked. But, usually, they do not do much more than stick to habitable surfaces. And occasionally they move. When they detach, they may curl into balls, which can help them fall and roll more safely to a new location.

The critical problem for chitons is that they are top-heavy but not flexible enough to twist and have no appendages. So when they accidentally land on their backs, they cannot flip back. All they can do is arch and thrust out their foot. With luck, they will touch something they can push off to right themselves – or a place to stick and stay safe. Their foot glue is so strong that if you were to lift a chiton off a rock too strongly, its body and shell would rip off, leaving the foot behind. And that makes the foot an important element of their defence against hungry predators, Sigwart says.

In each experimental trial, the researchers placed a chiton upside down in the middle of a test tank. Then, they added water from a tank with more chitons or a tank with an ochre sea star. Chitons can detect this natural predator’s scent. The researchers found that the chitons exposed to it were three times less likely to spend time rolled up than those that were not. These threatened chitons opted to arch and reach. It’s an energy-intensive defence that can risk exposing its soft body, but it can also reward a chiton by helping it find a safe place to survive.

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Original paleo diet recipe: cave-aged bone marrow

Sealed for millenniums, Qesem Cave in central Israel is a limestone time capsule of the lives and diets of palaeolithic people from 420,000 to 200,000 years ago. Inside, ancient humans once butchered fresh kills with stone blades and barbecued meat on campfires. “It was believed that early hominins were consuming everything they could put their hands on immediately, without storing or preserving or keeping things for later,” says Ran Barkai, an archaeologist at Tel Aviv University in Israel.

But not every meal was scarfed down right after a hunt. Barkai and his colleagues have found the cave’s earliest inhabitants may have also stored animal bones filled with tasty marrow that they feasted on for up to nine weeks after the kill, sort of like a stone age canned soup.

The finding may be the earliest example of prehistoric humans saving food for later consumption and may also offer insight into the abilities of ancient humans to plan for their future needs. The study was published in Science Advances. Barkai’s team examined cut marks on nearly 82,000 animal fragments from Qesem Cave, most belonging to fallow deer. The researchers noticed unusual, heavy chop marks on the ends of some leg bones known as the metapodials.

Usually, stripping the hide from a fresh bone requires minimal force, he says. But the heavy chops indicated that the processing used more force than should have been necessary. “We had a hypothesis that these unusual chop marks at the end of the meatless bones had to do with the removal of dry skin,” he says. But why were they doing that?

The team concluded the ancient hominins, who shared features with Homo sapiens and Neanderthals but were probably neither, were removing dry skin on the bones to get to the marrow. That presented another question: If they were after marrow, why not just remove it from the bone when it was fresh? The researchers hypothesised that the chop marks were an indication that the early humans stored the bones so they could eat the marrow later.

To test their idea, the team collected freshly killed deer leg bones and then stored them for several weeks in conditions similar to those inside the cave. After every week, they would break open a bone and analyse the marrow to see how nutritious it still was. Every time, a researcher would remove the dried skin using a flint flake and then hammer open the bone with a quartzite tool, similar to what the ancient people would have had used. The researcher wasn’t given instructions on how to open the bone.

The team found that the researcher’s chop marks on the older leg bones with dried skin were similar to what they saw in Qesem Cave. Their chemical test showed that after nine weeks, the fat in the bone marrow degraded only a little and was still nutritious.

Eight arms, 40 winks and who knows how many dreams?

Heidi the octopus is sleeping. Her body is still, eight arms tucked neatly away. But her skin is restless. She turns from ghostly white to yellow, flashes deep red, then goes mottled green and bumpy like plant life. Her muscles clench and relax.

From the outside, the cephalopod looks like a person twitching and muttering during a dream or like a napping dog chasing dream squirrels. But an octopus is almost nothing like a person. So how much can anyone really say with accuracy about what Heidi was doing?

It is only conjecture to say the octopus is dreaming without more data, says University of Cambridge psychologist Nicola Clayton. Does the sequence of Heidi’s colour changes match an experience she had while awake? Clayton points out that a human sleeper might flush red because she is overheated.

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The mysterious blob that didn’t come from outer space

When a giant fatberg was discovered in the sewer of a small coastal town in southwestern England last year, the company that manages the pipes was so mystified by the greasy mass of solidified fats and waste materials that it enlisted the help of scientists to discover what it was made of.

The grisly results of an autopsy held some surprises. Stuck within the stomach-churning lump were wet wipes, oils, sanitary products and even a set of false teeth.

Fatbergs are commonly associated with big cities such as London and New York. Their contents can become a taxonomy of the habits of the inhabitants of nearby towns or cities.

© New York Times