Thirst Circuits - Gynadromorph Birds - Evolving Blindness - Cannabis ODs

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Aug 13, 2025, 7:40:39 AMAug 13

https://www.quantamagazine.org/what-does-it-mean-to-be-thirsty-20250811/

What Does It Mean To Be Thirsty?

By Dan Samorodnitsky

Water is the most fundamental need for all life on Earth. Not every organism needs oxygen, and many make their own food. But for all creatures, from deep-sea microbes and slime molds to trees and humans, water is nonnegotiable. “The first act of life was the capture of water within a cell membrane,” a pair of neurobiologists wrote in a recent review. Ever since, cells have had to stay wet enough to stay alive.

Water is the medium in which all chemical reactions in an organism take place, and those reactions are finely tuned to a narrow range of ratios between water and salt, another essential ingredient in life’s chemistry. The cells in your body are permeable to water, so if the water-salt balance of the surrounding fluid — blood, lymph or cerebrospinal fluid, for example — is outside its healthy range, cells can swell or shrink, shrivel or potentially burst. An imbalance can cause brain cells to malfunction, losing their ability to manage ion concentrations across their membranes and propagate action potentials.

Although these effects of insufficient water are felt by every cell in the body, cells themselves do not cry out in thirst. Instead, it’s the brain that monitors the body’s water levels and manifests the experience of thirst — a dry tongue, hot throat and rapid onset of malaise — which compels a behavior: acquire water.

“These neural circuits that control hunger and thirst are located deep in primitive brain structures like the hypothalamus and brainstem,” said Zachary Knight (opens a new tab), a neuroscientist at the University of California, San Francisco, who recently co-authored a review paper in Neuron (opens a new tab) on the neurobiology of thirst.

Because these brain areas are difficult to study — due not only to their location, but also to their composition, with many different cell types and crisscrossed circuitry — it’s only in the last decade or so that neuroscientists have begun to understand how thirst fundamentally works. The body, researchers have found, is filled with sensors that feed clues to the brain about how much water or salt an organism needs to consume. How those sensors work, or what they even are, continues to elude scientists. Their existence offers a tantalizing insight: Water may be fundamental to life, but thirst is an educated guess.
© 2025 Simons Foundation

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https://www.science.org/content/article/sex-reversal-surprisingly-common-birds-new-study-suggests

‘Sex reversal’ is surprisingly common in birds, new study suggests

By Phie Jacobs

When it comes to telling males and females apart, many bird species reject subtlety altogether. Roosters stand out thanks to their big, bright comb and ear-splitting “cock-a-doodle-doo.” Bachelor birds-of-paradise flaunt their vibrant plumage to attract more subdued females. And the male peacock’s feathered train is so ostentatious it famously threw even Charles Darwin for a loop.

But that’s not the case for all bird species. When males and females look pretty much the same, scientists must try harder—often using DNA testing—to separate the sexes. According to a new study of wild Australian birds, these methods may be leading to misidentification in cases where an individual’s gonads and outward appearance don’t align with the genetic sex determined by its chromosomes. As scientists report today in Biology Letters, this phenomenon—known as sex reversal—may be more common than anyone expected.

The discovery is likely to “raise some eyebrows” (or is it ruffle some feathers?), says Blanche Capel, a biologist at Duke University who wasn’t involved in the new work. Although sex determination is often viewed as a straightforward process, she explains, the reality is much more complicated.

In humans, individuals with XX chromosomes typically develop as female, whereas those with XY chromosomes are usually male. But Judith Mank, a zoologist at the University of British Columbia, notes it’s the genes carried on those chromosomes—not the chromosomes—that are the main players. The SRY gene on the Y chromosome, for example, kick-starts male development in mammals. Anyone missing this key gene will end up developing as female, even if they have XY chromosomes. “We think of sex chromosomes as being sex determining,” says Mank, who also wasn’t involved in the new research. “That’s not true.”

What’s more, it can matter how these genes are expressed on a cell-by-cell basis. In some species such as fruit flies, zebrafish, and chickens, individual cells have their own sexual identity based on the genes they happen to contain or express, rather than being influenced by the body’s overall hormone levels. When different cells contain different sets of chromosomes, this process can give rise to individuals called gynandromorphs, which exhibit both male and female characteristics.

https://knowablemagazine.org/content/article/living-world/2025/how-the-cavefish-lost-its-eyes

How the cavefish lost its eyes — again and again

By Tim Vernimmen

Mexican tetras are a most peculiar fish species. They occur in many rivers and lakes across Mexico and southern Texas, where they look perfectly ordinary. But unlike most other fishes, tetras also live in caves. And there, in the absence of light, they look dramatically different: They’re very pale and, remarkably, they lack eyes.

Time and again, whenever a population was swept into a cave and survived long enough for natural selection to have its way, the eyes disappeared. “But it’s not that everything has been lost in cavefish,” says geneticist Jaya Krishnan of the Oklahoma Medical Research Foundation. “Many enhancements have also happened.”

Though the demise of their eyes continues to fascinate biologists, in recent years attention has shifted to other intriguing aspects of cavefish biology. It has become increasingly clear that they haven’t just lost sight, but also gained many adaptations that help them to thrive in their cave environment, including some that may hold clues to treatments for obesity and diabetes in people.

It has long been debated why the eyes were lost. Some biologists used to argue that they just withered away over generations because cave-dwelling animals with faulty eyes experienced no disadvantage. But another explanation is now considered more likely, says evolutionary physiologist Nicolas Rohner of the University of Münster in Germany: “Eyes are very expensive in terms of resources and energy. Most people now agree that there must be some advantage to losing them, if you don’t need them.”

Scientists have observed that mutations in different genes involved in eye formation have led to eye loss. In other words, says Krishnan, “different cavefish populations have lost their eyes in different ways.”

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https://www.nytimes.com/2025/08/10/health/cannabis-poisoning-children.html

Cannabis Poisonings Are Rising, Mostly Among Kids

By Danielle Ivory. Julie Tate and Megan Twohey

Amy Enochs was texting with other parents, all wondering why their central Ohio elementary school had gone into lockdown, when the school called. Several fourth graders, including Ms. Enochs’s daughter, had eaten marijuana gummies and were being taken to the hospital with racing pulses, nausea and hallucinations.

A classmate had found the gummies at home and mistaken them for Easter candy.

Ms. Enochs recalled hyperventilating that spring day three years ago. “I was scared to death,” she said, her voice breaking. “It was shock and panic.”

As legalization and commercialization of cannabis have spread across the United States, making marijuana edibles more readily available, the number of cannabis-related incidents reported to poison control centers has sharply increased: from about 930 cases in 2009 to more than 22,000 last year, data from America’s Poison Centers shows. Of those, more than 13,000 caused documented negative effects and were classified by the organization as nonlethal poisonings.

These numbers are almost certainly an undercount, public health officials say, because hospitals are not required to report such cases. More than 75 percent of the poisonings last year involved children or teenagers.

In most instances of cannabis exposure, the physical effects were not severe, according to the poison control data. But a growing number of poisonings have led to breathing problems or other life-threatening consequences. In 2009, just 10 such cases were reported to poison centers; last year, there were more than 620 — a vast majority of them children or teens. More than 100 required ventilators.