News and notes about science
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 March 5 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, said 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 molds 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 molds 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 said.
But when the volunteers returned for more testing, after a week wearing the little molds 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, said 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. Veronique Greenwood
A SUPERCOLONY OF PENGUINS HAS BEEN FOUND NEAR ANTARCTICA
A new colony of Adélie penguins has been discovered near Antarctica, substantially increasing the known populations of the knee-high creatures.
“It’s always good news when you find new penguins,” said P. Dee Boersma, director of the Center for Ecosystem Sentinels at the University of Washington, who was not involved in the new study. “The trends have not been good for so many of these species.”
Previous censuses of penguins had come close to these animals, living on the Danger Islands just off the end of the “thumb” of Antarctica, below South America. But satellite images of the islands revealed the pinkish-red stain of penguin guano, suggesting larger colonies than expected, said Heather Lynch, one of the five primary investigators on the new study, published March 9 in Scientific Reports.
After several years of preparation, a team of researchers traveled in 2015 to the Danger Islands near the Weddell Sea to do a more precise count on the nine-island archipelago. Using a drone doctored to work in the extreme climate of the region, the researchers were able to get a precise estimate of the numbers of breeding pairs of Adélie penguins in the region: about 750,000 (or 1.5 million individuals).
Lynch said researchers had already known about a population on Heroina Island, at the northeast end of the Danger Islands chain. Now they’ve found that sizable populations live on other islands near Heroina.
The greater numbers will help ensure that conservation efforts focus on keeping them safe, she said.
“This area falls between two marine-protected areas that are being planned right now,” she said. And until this discovery, the Danger Islands “wasn’t considered a high priority for protection.”
One of the surprises of the study, Lynch said, was that the Danger Islands penguins don’t nest in a circular pattern, as would be expected, to provide the best protection from predators. Instead, they seem to be faithful to individual nesting spots, prizing habit over safety, she said. Karen Weintraub
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 behavioral 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 analyzed 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 2 to 3 kilohertz. “No one has ever described that a bird can hear even above 8, 9 kilohertz,” said Mello.
But “the fundamental frequency of those calls was above 10 kilohertz,” he said. “That’s what was really amazing.”
The findings, published March 5 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. Douglas Quenqua
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 March 7 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, said 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. Joanna Klein
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 March 6 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 suggested, 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, said Sandrine Henri, a researcher at the Immunology Center 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,” said 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 synthesize 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 tattoobearing 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 1 in 5 adults in the United States have at least one tattoo, and tens of thousands of laser removals are performed each year. Steph Yin