Evolving Bitter - Dawn Song - Seeing Circles - Stress & Sleep

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Jun 21, 2025, 7:30:10 AMJun 21

https://www.science.org/content/article/no-sour-faces-how-birds-evolved-eat-highly-acidic-fruits

No sour faces: How birds evolved to eat highly acidic fruits

By Nazeefa Ahmed

Humans prefer fruit at its sweetest, whereas many birds happily snack on the sourest of the bunch, from zesty lemons to unripe honey mangoes. Researchers may now know why.

A study published today in Science suggests birds have evolved a specialized taste receptor that’s suppressed by high acidity, which effectively dulls the sharp, sour taste of fruits they eat. The finding reveals the evolutionary history of the pucker-inducing diets of many fruit-eating birds around the world—and may also help explain birds’ knack for survival, by broadening their potential food sources.

The study is a “robust” addition to our understanding of how birds taste sour foods, which is still a research area in its infancy, says Leanne Grieves, an ornithologist at Cornell University’s Lab of Ornithology. Scientists identified a sour taste receptor in vertebrates—known as OTOP1—only 7 years ago, and few studies focus on why birds eat what they eat, rather than simply what they eat. Grieves, who studies birds’ sense of smell but who was not involved with the current work, adds that the new study “provides a really nice starting point.”

To examine how birds approach sour-tasting foods, scientists exposed OTOP1 receptors from mice, domestic pigeons, and canaries to various acidic solutions. The activity of the mouse version of the receptor increased with greater acidity—meaning more acidic foods register to mice, and other mammals like us, as increasingly sour. However, the pigeon and canary versions of OTOP1 became less active in solutions about as acidic as a lemon. As a result, the birds wouldn’t perceive as much of a sour taste, allowing them to take advantage of the fruits mammals can’t stomach.

Determining why bird OTOP1 reacted differently was a challenge, according to study author Hao Zhang, an evolutionary biologist at the Chinese Academy of Sciences (CAS). So, the researchers mutated sections of the gene that encodes the OTOP1 receptor, which let them identify four candidate amino acids within the protein that are responsible for sour tolerance. One of them, known as G378, is found almost exclusively in songbirds such as the canary—a species that showed greater sour tolerance than the pigeon, which lacks this variance. “A single amino acid in the bird OTOP1 can increase sour tolerance,” says study author Lei Luo, a biologist at CAS.

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https://www.npr.org/2025/06/20/nx-s1-5436078/why-birds-sing-dawn-chorus-research-study

A new study knocks down a popular hypothesis about why birds sing at dawn

James Doubek

Researchers have some new evidence about what makes birds make so much noise early in the morning, and it's not for some of the reasons they previously thought.

For decades, a dominant theory about why birds sing at dawn — called the "dawn chorus" — has been that they can be heard farther and more clearly at that time.

Sound travels faster in humid air and it's more humid early in the morning. It's less windy, too, which is thought to lessen any distortion of their vocalizations.

But scientists from the Cornell Lab of Ornithology's K. Lisa Yang Center for Conservation Bioacoustics and Project Dhvani in India combed through audio recordings of birds in the rainforest. They say they didn't find evidence to back up this "acoustic transmission hypothesis."

It was among the hypotheses involving environmental factors. Another is that birds spend their time singing at dawn because there's low light and it's a bad time to look for food.

"We basically didn't find much support for some of these environmental cues which have been purported in literature as hypotheses" for why birds sing more at dawn, says Vijay Ramesh, a postdoctoral research associate at Cornell and the study's lead author.

The study, called "Why is the early bird early? An evaluation of hypotheses for avian dawn-biased vocal activity," was published this month in the peer-reviewed journal Philosophical Transactions of the Royal Society B.

The researchers didn't definitively point to one reason for why the dawn chorus is happening, but they found support for ideas that the early morning racket relates to birds marking their territory after being inactive at night, and communicating about finding food.

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https://www.science.org/content/article/culture-literally-changes-how-we-see-world

Culture literally changes how we see the world

By Nala Rogers

Coffer illusion

What do you see when you stare at this grid of line segments: a series of rectangles, or a series of circles? The way you perceive this optical illusion, known as the Coffer illusion, may tie back to the visual environment that surrounds you, a recent preprint suggests.

Himba people from rural Namibia can see right through optical illusions that trick people from the United States and United Kingdom. Even when there’s no “right” or “wrong” way to interpret an image, what Himba people see is often vastly different from what people see in industrialized societies, a new preprint suggests. That could mean people’s vision is fundamentally shaped by the environments they’re raised in—an old but controversial idea that runs counter to the way human perception is often studied.

For example, when presented with a grid of line segments that can be seen as either rectangles or circles—an optical illusion known as the Coffer illusion—people from the U.S. and U.K. almost always see rectangles first, and they often struggle to see circles. The researchers suspect this is because they are surrounded by rectangular architecture, an idea known as the carpentered world hypothesis. In contrast, the traditional villages of Himba people are composed of round huts surrounding a circular livestock corral. People from these villages almost always see circles first, and about half don’t see rectangles even when prompted.

“I’m surprised that you can’t see the round ones,” says Uapwanawa Muhenije, a Himba woman from a village in northern Namibia, speaking through an interpreter over a Zoom interview. “I wonder how you can’t see them.” Muhenije didn’t participate in the research because her village is less remote than those in the study, and it includes rectangular as well as circular buildings. She sees both shapes in the Coffer illusion easily.

Although the study found dramatic differences in how people see four illusions, “the one experiment that’s going to overwhelm people is this Coffer,” says Jules Davidoff, a psychologist at the University of London who was not involved in the study. “There are other striking cultural differences in perception, but the one that they’ve produced here is a real humdinger.” The findings were published as a preprint on the PsyArXiv in February and updated this week.

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https://www.nature.com/articles/d41586-025-01910-6

Revealed: how the brain turns stress into a bad night’s sleep

Katie Kavanagh

Scientists have identified a group of neurons that might explain the mechanism behind how stress gives rise to problems with sleep and memory.

The study — published last week in The Journal of Neuroscience1 — shows that neurons in a brain area called the hypothalamus mediate the effects of stress on sleep and memory, potentially providing a new target for the treatment of stress-related sleep disorders.

Previous work has shown that in the hypothalamus, neurons in a structure called the paraventricular nucleus communicate with other areas important for sleep and memory. The neurons of the paraventricular nucleus release a hormone called corticotropin and have a role in regulating stress. But the neural mechanisms underlying the effect of stress on sleep and memory have remained elusive.

For co-author Shinjae Chung, a neuroscientist at the University of Pennsylvania in Philadelphia, the question of exactly how stress affects these processes is personal, because, she says, “I experience a lot of sleep problems when I’m stressed”. She adds that “when I have an exam deadline, I have a tendency to have bad sleep that really affects my score the next day”.

To study how neurons in the paraventricular nucleus translate stress into sleep and memory problems, the researchers put laboratory mice through a stressful experience by physically restraining the animals in a plastic tube. The team then tested the creatures’ spatial memory and monitored their brain activity as they slept.