Science news in brief: Inside a pitcher plant and the cells that eat your tattoos

A roundup of news from around the world

How carnivorous plant species function may reveal the secrets of plant and insect life (Alamy)

The weird world inside a pitcher plant

On the soggy floor of one of the only remaining intact forests on the island nation of Singapore, the egg-sized heads of carnivorous creatures emerge from decaying leaves. They appear to be belching, or singing, or screaming.

This is Nepenthes ampullaria, an unusual pitcher plant found on the islands of Southeast Asia and the Malay Peninsula. The worm larva of Xenoplatyura beaveri, a species of fungus gnat, develops inside the plant’s mouth. When grown, it looks like a mosquito with big biceps.

The plant gives the gnat baby a safe place to eat and develop. In exchange, the baby builds a web across the plant’s lips, captures and eats other insects and then defecates into its maw, or pitcher. The plant eats the ammonium-rich droppings.

It’s not romantic. It’s not sweet. But researchers call this relationship “mutualistic” in a study published in Biology Letters. Their findings, based on laboratory experiments that simulated this insect-plant interaction in the wild, suggest that cohabitation may have its benefits for these two obscure organisms. How tiny pitcher plant communities like this one and others the group is studying function may reveal secrets of plant and insect life, says Weng Ngai Lam, a graduate student in botany at the National University of Singapore, who led the research.

These pitcher plants carry out a quirky version of their family’s strategies for surviving in a nutrient-poor environment. The alien mouths of pitcher plants are really just modified leaves shaped like fairy pottery and connected by a vine that can climb dozens of feet into the forest canopy. The pitchers collect rainwater and juices the plant secretes. Animals, mostly insects and the occasional crab or frog, find shelter and grow up inside this wet mouth.

But others get trapped and die there. Their proteins, once broken down, provide nutrients like nitrogen and phosphorus deficient in the soil.

Most species of pitcher plants lure prey into acid-filled pitchers with nectar-coated lips. The prey falls in, drowns and dissolves on contact.

But N ampullaria is different. It makes less nectar and its juices are less acidic, and can’t seem to dissolve insects whole. Instead, it consumes fallen leaves and depends more on its inhabitants to break down its prey.

The cells that eat, regurgitate and eat your tattoos again

We think of tattoos as fixed adornments. Plunge ink deep enough into the skin and there it will sit, suspended in subterranean connective tissue forever.

But tattoos are actually maintained by an ever-changing process – one in which ink crystals are continuously engulfed, regurgitated and gobbled back up, merely giving the illusion of stasis.

That’s what French scientists observed from studying tatted mice. In their model of tattoo persistence, published in the Journal of Experimental Medicine, macrophages – immune cells that ingest foreign or unhealthy debris in the body – play a starring role. Targeting these cells, the authors suggest, might help improve tattoo removal procedures for people.

As a tattoo is given, macrophages descend to capture invading ink. Probably because the ink granules are too bulky for the microscopic Pac-Mans to break down, they hold onto the pigment, your body art shining through their bellies.

With time, these original macrophages die and release their pigments, which get vacuumed up by new macrophages, starting the cycle over, says Sandrine Henri, a researcher at the Immunology Centre of Marseille-Luminy who led the study with her colleague Bernard Malissen.

This research “shows that tattoos are in fact much more dynamic than we previously had believed,” says Johann Gudjonsson, a professor of immunology and dermatology at the University of Michigan who was not involved in the study.

For years, researchers suspected that tattoos worked by permanently staining fibroblasts, the cells that synthesise collagen, under the surface of our skin.

Then, looking at tattoo biopsies under the microscope, scientists saw macrophages laden with ink globules, and the story of tattoos became one of the immune system. Still, it was thought that tattoo-bearing macrophages were stable and long-lived, giving tattoos their permanence. What this study suggests is that, at least in mice, these macrophages are constantly being replaced.

The authors speculate that targeting macrophages might enhance laser removal, which can take as many as 20 treatments. An estimated one in five adults in the United States have at least one tattoo, and tens of thousands of laser removals are performed each year.

How the shape of your ears affects what you hear

Researchers have discovered that filling in an external part of the ear with a small piece of silicone drastically changes people’s ability to tell whether a sound came from above or below. But given time, the scientists show in a paper published in the Journal of Neuroscience, the brain adjusts to the new shape, regaining the ability to pinpoint sounds with almost the same accuracy as before.

Scientists already knew that our ability to tell where a sound is coming from arises in part from sound waves arriving at our ears at slightly different times. If a missing cellphone rings from the couch cushions to your right, the sound reaches your right ear first and your left ear slightly later. Then, your brain tells you where to look.

But working out whether a sound is emanating from high up on a bookshelf or under the coffee table is not dependent on when the sound reaches your ears. Instead, says Régis Trapeau, a neuroscientist at the University of Montreal and author of the new paper, the determination involves the way the sound waves bounce off outer parts of your ear.

The researchers set up a series of experiments using a dome of speakers, ear moulds made of silicone and an fMRI machine to record brain activity.

Before being fitted with the pieces of silicone, volunteers heard a number of sounds played around them and indicated where they thought the noises were coming from. In the next session, the same participants listened to the same sounds with the ear moulds in. This time it was clear that something was different.

“We would put a sound above the participant’s head, and he would say it’s below,” Trapeau says.

But when the volunteers returned for more testing, after a week wearing the little moulds in their ears, most saw their scores go back up. We’re able to locate sound with our own ears because we know their shape, says Trapeau. When that shape changes, we need time and practice to adapt to it.

The researchers discovered that as sounds originate from higher locations, the neurons respond less and less. That means that the neurons are likely representing height by the magnitude of their response.

This hummingbird chirps like an insect. Can it hear its own sound?

Claudio Mello was conducting research in Brazil’s Atlantic Forest about 20 years ago when he heard a curious sound. It was high-pitched and reedy, like a pin scratching metal.

A cricket? A tree frog? No, a hummingbird.

At least that’s what Mello, a behavioural neuroscientist at Oregon Health and Science University, concluded at the time. Despite extensive deforestation, the Atlantic Forest is one of Earth’s great cradles of biological diversity. It is home to about 2,200 species of animals, including about 40 species of hummingbirds.

In 2015, Mello returned to the forest with microphones used to record high-frequency bat noises. The recordings he made confirmed that the calls were coming from black jacobin hummingbirds. The species is found in other parts of South America, too, and researchers are unsure whether the sound is emitted by males, females or both, although they have confirmed that juvenile black jacobins do not make them.

When Mello and his team analysed the noise – a triplet of syllables produced in rapid succession – they discovered it was well above the normal hearing range of birds. Peak hearing sensitivity for most birds is believed to rest between two to three kilohertz. “No one has ever described that a bird can hear even above eight, nine kilohertz,” says Mello.

But “the fundamental frequency of those calls was above 10 kilohertz,” he says. “That’s what was really amazing.”

The findings, published in the journal Current Biology, suggest that black jacobins either can hear sounds that other birds cannot, or cannot hear the sounds they are making.

Though additional study is needed to be sure, Mello considers it unlikely that a bird would evolve to make noises it can’t detect. Instead, he believes the hummingbirds have adapted to the cacophony of their environment by finding their own wavelength on which to communicate.

© New York Times