Platypuses face a dammed, inbred future
News and notes about science
The duck-billed platypus faces many threats — climate change, loss of habitat, pollution and invasive species, among others. Although they are not yet considered endangered, their numbers are declining, and some local populations have become extinct. Now, scientists have found yet another manufactured menace: the construction of dams in the rivers they inhabit.
Platypuses are semiaquatic egg-laying mammals. Despite being only 1 to 2 feet long, they can climb over dams, at least smaller ones. And although they can avoid the artificial obstacles by walking on land, predation by red foxes, as well as both feral and domestic cats and dogs, presents them with additional risks.
In a study published recently in the journal Communications Biology, scientists found that dams are restricting platypus migration and leading to inbreeding. Interference with migration can lead to genetic weaknesses, but until now, there has been no solid data to prove it was happening among platypuses.
Over two years, the study’s researchers examined platypus populations in five rivers with dams and four without in southeast Australia, collecting blood samples from 274 individuals to study their DNA. With this genetic analysis in hand, the scientists could see that dams posed a serious threat, not only because they destroy habitat but also from an evolutionary point of view. On a genetic level, the difference between populations living in dammed and undammed rivers was stark.
“When there is no migration between populations, and the populations are small, the genetic diversity within each group drops quickly,” said Luis Mijangos, a researcher at the University of New South Wales in Australia and an author of the study.
Platypuses only live naturally in eastern Australia and Tasmania, and there are an estimated 300,000 left in the world. In dammed rivers, they are divided into small, genetically distinct groups above and below the dam, a recipe for inbreeding and reduced numbers.
In Mijangos’ view, along with climate change and platypuses accidentally drowned in fishing nets, dams are one of most significant threats to the animals’ survival.
The World Wildlife Fund-australia is working on a project to restore a wild platypus population in the Royal National Park in Sydney. The group plans to do some other “re-wilding” projects in other areas in the future, none of which involve the dams. To Mijangos, their future still seems grim.
— Nicholas Bakalar
It looks like a shell, but it’s home to an octopus and 40,000 eggs
Argonauta Argo is not a typical octopus. When a female mates, first she keeps her partner’s detachable, sperm-filled limb inside of her. Then she begins making something like a handbag.
She uses the tips of two of her bluesheened arms to secrete a mineral formula, crafting it into a paper-thin basket shaped like a shell. The construction can grow to nearly 1 foot in length, becoming the home of more than 40,000 embryos. The argonaut octopus crawls inside its shell-like purse, traps some air bubbles inside, then uses its buoyancy to bob just beneath the surface of water in warm oceans around the world.
This egg holder has such an uncanny resemblance to the hard shells of the Nautiloids, the octopus’s distant relatives, that scientists nicknamed the argonaut the “Paper Nautilus.” But now, genetic sequencing data reveals the octopus independently evolved the genes to make its intricate embryo armor, instead of repurposing DNA it inherited from its shelled-ancestors.
These findings upend some misconceptions among scientists about how cephalopods evolved, said Davin Setiamarga, a researcher at the National Institute of Technology, Wakayama College in Japan, who detailed the new data recently with colleagues in the journal Genome Biology and Evolution.
The last common ancestor of most cephalopods likely had a chambered, pearly shell, not unlike the iconic one worn by the nautilus. But over millions of years of evolution, soft-bodied cephalopods like octopuses, squids and cuttlefish evolved to internalize that outer shell and shrink it while adapting to their individual habitats.
Because the argonaut still carries around a nautilus-shell-like construction, it has fueled the scientific debate about whether, and how, an animal can lose such a structure during the course of evolution, then get it back. Other researchers initially speculated that argonauts reactivated archaic genes from the mollusk era to form their egg case. But after sequencing the genome of A. argo from samples collected in the Sea of Japan, the data suggested otherwise. Like their nautilus relatives, scientists found that argonauts have protein-coding genes needed to build what scientists call “true shells,” the kind you find around an oyster. But they use entirely different genes than the nautilus do to make these formations. It means the shelllike egg case didn’t evolve from the ancestral shell, but it is the argonauts’ own evolutionary innovation for a new purpose.
— Sofia Quaglia
How brains send a signal that it’s time to vomit
Anyone who’s had a shady oyster or a mushroom soup that didn’t sit well remembers the ominous queasiness heralding impending bad times. Bacteria release toxins that start the body’s process of speedily evacuating the contents of the stomach. It’s a protective mechanism of sorts, but it has remained something of a mystery how the brain gets the alarm signal, then sends another one to tell the stomach to initiate a technicolor yawn.
Your next bout of food poisoning isn’t the only reason to understand this particular neural pathway. Figuring out how to counter it could be helpful for people who develop nausea caused by chemotherapy medication and other drugs.
In a new study, researchers report that both bacteria and chemotherapy drugs appear to trigger the same molecular pathways in the gut. The findings, which were based on experiments with mice and published recently in the journal Cell, showed that a bacterial toxin and a chemo medication both set in motion a cascade of similar neural messages that cause queasiness.
Cao Peng, a professor at Tsinghua University in Beijing, and his colleagues wondered whether mice might still be capable of feeling ill in the way people do after ingesting a chemo drug or a bad salad — or close enough, anyway, that researchers could use the creatures to understand the origins of the sensation.
The researchers gave the mice a bacterial toxin and watched them closely with high-speed cameras, and they found that the rodents started opening their mouths oddly after the treatment. More tests showed that their abdominal muscles were moving much like the way humans’ stomachs do when they are about to be sick. A chemo drug had the mice behaving similarly.
They traced the effect to certain neurons in the brain that released neurotransmitters when the drug or the toxin reached the gut. Following those messages back, they discovered cells in the small intestine that reacted to the presence of these noxious substances. A central player in the pathway to nausea and retching was an immune system molecule called interleukin 33, or IL33. Keeping mice from making IL33 significantly reduced their symptoms.
It’s possible that drugs that interfere with IL33 or other players in this pathway could help to alleviate the suffering of people having chemotherapy, Cao said.
— Veronique Greenwood
‘Planet killer’ asteroid spotted that poses distant risk to Earth
Astronomers on the hunt for modestly sized asteroids that could vaporize a city or bulkier beasts that could sterilize Earth’s surface have spotted a new potential threat. But there’s no immediate need to worry — it’ll be many generations until it may pose a danger to our planet.
Detecting uncharted space rocks relies on spying sunlight glinting off their surfaces. But some asteroids occupy corners of the sky in which the sun’s glare smothers them, and, like embers flitting in front of a thermonuclear bonfire, they fade from view.
Last year, in the hope of finding asteroids cloaked by excessive sunlight, an international team of astronomers co-opted a camera primarily designed to investigate the universe’s notoriously elusive dark energy. In an announcement recently based on a survey first published in September in The Astronomical Journal, the researchers announced the discovery of three new light-drowned projectiles.
One of them, 2022 AP7, is roughly a mile long, and its orbit crosses Earth’s path around the sun, getting as near as 4.4 million miles to Earth itself. That makes 2022 AP7 “the largest potentially hazardous asteroid found in the last eight years or so,” said Scott Sheppard, an astronomer at the Carnegie Institution for Science in Washington, D.C., and an author of the study.
After the asteroid was discovered in January, additional observatories studied its motion and other astronomers retrospectively identified it in older images. This data set made it clear that it won’t be paying Earth a visit during the next century and perhaps far longer.
And if, in the unluckiest of timelines, 2022 AP7 ultimately impacts Earth?
“This is what we call a planet killer,” Sheppard said. “If this one hits the Earth, it would cause planetwide destruction. It would be very bad for life as we know it.”
But as we are safe for many generations, this asteroid’s orbit is not its most noteworthy feature. Its existence suggests that other elephantine asteroids, veiled by the sun’s glare, remain disconcertingly undiscovered.
Today, astronomers looking for potentially hazardous asteroids — those that get at least as close as 4.6 million miles to Earth and are too chunky to be incinerated without incident by our atmosphere — focus on finding rocks around 460 feet across. Such threats have motivated NASA and other space agencies to develop planetary defense missions like DART, the spacecraft that successfully adjusted the orbit of a small, nonthreatening asteroid in September.
— Robin George Andrews