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Science news in brief: Marmots longer lives and self-fertilising worms

A round-up of science stories from around the world

Marmots prefer to live solitary lives, but will peacefully coexist with one another if the habitat demands it
Marmots prefer to live solitary lives, but will peacefully coexist with one another if the habitat demands it (Inklein)

Being anti-social leads to a longer life – for marmots

For many mammals, a busy social life can be an important contributor to a long life. But some animals need more alone time than others, and failure to get it could be lethal, according to new research.

Consider the marmot. After spending 13 years tracking their interactions and life spans in Colorado, Daniel T Blumstein, a biologist at the University of California, Los Angeles, and his colleagues found in a study published in Proceedings of the Royal Society B that yellow-bellied marmots with more active social lives tended to die younger than those that avoided interactions.

“The difference in life span between the most social and the least social marmot was about two years,” Blumstein says. That’s significant considering that the average life span of a yellow-bellied marmot is about 15 years.

Marmots are a genus of large, squirrel-like rodents with sharp claws and furry ears. They are known as socially flexible animals: they prefer to live solitary lives, but will peacefully coexist with one another if the habitat demands it.

“The yellow-bellied marmot is more social than other marmots, like the groundhog, but it doesn’t really want to be social,” says Blumstein.

If a yellow-bellied marmot population grows too large, leading to a strain on habitable space, a female yellow-bellied marmot will sometimes allow her daughters to settle nearby, and about half will accept the invitation.

Why socialising might be detrimental to a marmot’s health is hard to say. Perhaps, Blumstein speculated, the animals are passing diseases among themselves. Maybe they are more likely to wake one another during hibernation, causing them to starve in the barren winter forest. Or perhaps time they spend socialising would be better spent looking out for predators.

The findings offer a contrast with other mammals. Many studies have shown that highly social animals live longer if they maintain strong social networks,” he says. “For humans, not being social is about as bad as smoking a pack or so of cigarettes a day.”

The worm that evolved self-fertilisation and lost a quarter of its DNA

Inspecting the tiny roundworms Caenorhabditis briggsae and Caenorhabditis nigoni through a microscope, you’d have trouble telling them apart. Both are about 1mm long and transparent. On the evolutionary tree, they’re closer together than horses and donkeys.

The key distinction between the two nematodes is their sex lives. Sex in C nigoni takes place between a male and female. But only a small minority of C briggsae are males. The rest are hermaphroditic females that reproduce by self-fertilising, or selfing. They have evolved the ability to produce sperm that merge with their own eggs.

This sexual switch may have caused profound changes at the genetic level for C briggsae. In a study published this month in Science, biologists reported that C. briggsae lost thousands of genes – a staggering quarter of its genome – since it diverged from C nigoni a million years ago.

“Many of these genes had been around, and were presumably needed, for tens of millions of years or longer,” says Eric Haag, a biology professor at the University of Maryland, College Park, and an author of the paper. “In the blink of an eye, they disappeared.” He and his co-authors believe that a large portion of the genes shed are related to male reproduction.

In their study, the biologists compared C. briggsae and C. nigoni, and discovered that C. briggsae has about 7,000 fewer genes. A disproportionately high number of shed genes, they found, were more heavily expressed in male than female C. nigoni.

“That tells us that the stuff being lost in Caenorhabditis briggsae is disproportionately involved in male biology,” says Erich Schwarz, an assistant research professor at Cornell University who led the sequencing efforts for the study.

Are earthquakes more likely during full moons? Not so

In 2004 a magnitude 9.1 earthquake ruptured the ocean floor off the west coast of Sumatra. The resulting tsunami killed nearly 230,000 people in 14 countries, making it one of the deadliest natural disasters in history. And it occurred during a full moon.

The Sumatra earthquake isn’t the only large earthquake to have occurred beneath the moon’s bright glare. Both the earthquake that devastated Chile in 2010 and the Great Alaskan Earthquake in 1964 also happened on a conspicuous lunar date – making it tempting to argue that more large earthquakes occur during the full moon.

But a new study published in Seismological Research Letters finds that the connection is nothing but folklore.

To analyse the supposed link, Susan Hough, a seismologist at the US Geological Survey, scrutinised 204 earthquakes of magnitude 8 or greater over the past four centuries. She then matched those earthquakes to the lunar calendar and found that no more occurred during a full or new moon than on any other day of the lunar cycle.

“The lore that the big earthquakes happen during the full moon — there’s no support for that in the catalog,” Hough says.

There is some sound science connecting Earth’s temblors and the moon. That’s because during full and new moons, Earth, the sun and the moon fall along a nearly straight line. This celestial alignment tugs at our planet, raising tides in the oceans and in the solid earth.

That effect is far too weak to cause an earthquake on its own. But should the moon’s gravitational pull tug at a fault that is dangerously close to rupture, a temblor is not impossible.

“It’s not some wild crazy idea,” Hough says.

But the gravitational effect is vanishingly small and only occurs under narrow circumstances, so it would never translate into a pronounced force – certainly not one that can be seen in a calendar or used to make predictions.

In short, Hough’s study “debunks the prevalent superstition some people have that the moon tells us something about the danger,” says John Vidale, a seismologist at the University of Southern California who directs the Southern California Earthquake Centre and was not involved in the new study.

A wet and warm spring, then 200,000 dead saigas

Among saiga antelopes, the month of May ought to be about new life. But in 2015, it was just the opposite for the Betpak-Dala saiga population in central Kazakhstan.

In only three weeks, about 220,000 of the critically endangered antelopes, most of them newborns and mothers that had gathered to calve, dropped dead across an area the size of Britain.

In a study published in Science Advances, researchers presented a preliminary account of the cause of the mysterious die-off: bacteria called Pasteurella multocida, which seem normally to exist harmlessly in saigas’ tonsils, somehow invaded their guts, poisoning their blood and breaking down their organs, leading to death within a few hours.

The mechanism that allowed the bacteria to become so harmful is still unclear, but the scientists believe it had something to do with a peculiarly wet and warm period before the outbreak.

“One possible explanation might be that climate change is driving these events,” says Richard Kock, a professor at the Royal Veterinary College in London and an author of the paper. There have been a series of such die-offs in recent years, he noted, but the team found no evidence for these events before the 1980s.

Scientists now need to model how climate change might affect saigas in the future, particularly if unusually wet and warm weather events become more common in their range.

In the new study, Kock and his colleagues first confirmed that P multocida was the immediate cause of death in 2015. They found nothing significant in the soil or the vegetation the antelopes had been exposed to, and determined that the animals were not nutritionally deficient or immunosuppressed.

What did show a strong correlation with the die-off in 2015 were the average relative humidity and average minimum temperatures in the 10 days leading up to mass mortality. During these 10 days, if relative humidity is greater than 80 per cent, there’s a strong possibility of outbreak, says Wendy Beauvais, a postdoctoral student in veterinary medicine at Cornell University and an author of the study.

It is clear that an environmental trigger allowed the bacteria to wreak havoc, but how remains a mystery, Kock says. The 100 per cent fatality rate that occurred in 2015 was unprecedented among similar outbreaks in other large mammals.

Where did animals with tail weapons go? Here’s a back story

With a nearly impenetrable hide covered in spikes, the ankylosaurus was like a dinosaur version of an armored tank. And like any battlefield behemoth, it boasted a fearsome weapon: a bone-crushing clubbed tail.

The ankylosaurus was not the only prehistoric beast to have an intimidating backside. Stegosaurus sported spear-like spikes on its tail. Some sauropods flailed fused clumps of bones from their posteriors toward predators.

But in living animals today, formidable tail weaponry is nearly absent. Although porcupines have quills and some lizards lash their tails when threatened, neither animal has the bony armaments seen millions of years ago. A pair of paleontologists has pieced together a series of traits shared among extinct species that had weaponised their fifth extremity. Their study may help explain why tail weaponry has gone missing since dinosaurs and some ice age animals went extinct.

In a paper published this month in the journal Proceeding of the Royal Society B, the team has identified three characteristics in land-dwelling mammals, reptiles and nonavian dinosaurs that may be linked with evolving bony tail weapons. They include being large — about the size of a mountain goat or bigger — eating plants and already having an armored body.

“That’s a really rare combination no matter what time period you’re looking at,” says Victoria Arbour, a paleontologist at the University of Toronto and the Royal Ontario Museum and an author on the study.

Arbour and her colleague Lindsay Zanno, a paleontologist from North Carolina State University, were sure to note that the three traits they identified are correlated with animals that have tail weapons and do not drive the development of these dangerous appendages.

The authors hypothesised that developing bony clubs like the ankylosaurus and the glyptodon was a gradual, evolutionary process. Living animals tend to have tails with weapons that are made of keratin, like the quills of a porcupine or the scales of a pangolin.

Reporting by Douglas Quenqua, Steph Yin, Shannon Hall and Nicholas St Fleur

© New York Times

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