Just a blob of cells? Well, just wait 26 seconds
News and notes about science
Researchers at the Howard Hughes Medical Institute’s Janelia Research Campus in Ashburn, Va., have built a new microscope that can trace individual cells’ origins and movement in realtime, sketching a virtual map of how mammals develop in the womb.
The photos, taken in a span of 26 seconds, show a blob’s tiny cells multiply, interact and organize into the first organ systems of a living mouse embryo. The hollow crater that forms on the left of the blob will give rise to the mouse’s stomach, pancreas and liver.
The narrow white line that begins to stretch across the center of the images is the notochord, or an early backbone.
The results, published recently in the journal Cell, could have critical applications for understanding how organ systems form in humans as well, potentially assisting treatments of birth defects.
“We have been previously limited to snapshots in time, like reading random pages torn out of a book,” said Kate Mcdole, a developmental biologist and one of the study’s co-authors. “But how are the organs actually formed? What’s the timing, the tissues, the dynamics that are involved? You can only study that by looking at it live.”
The research team, led by Philipp Keller, a physicist and biologist, set out to overcome the limitations of confocal microscopy, a traditional imaging method that casts light through an entire specimen for extended periods of time.
That method was too harsh for the delicate embryonic cells of a mouse. “You’d basically be microwaving it,” Mcdole said.
The new microscope — a clear, acrylic cube with a central chamber — has two cameras and two razor-thin sheets of light illuminating only small portions of the specimen as it bobs in a nutrient-rich fluid. Every few milliseconds, algorithms take into account the changing position of the embryo, the angle at which the light sheets are striking it, and the best direction from which to capture a clear image.
The team collected almost 1 million frames of each live embryo and compiled them, Keller said.
Scientists are not permitted to experiment with human embryos. But by visualizing how organs form in mice, this research could help doctors investigate developmental issues inside the human womb.
— Emily Baumgaertner
City rats eat meat; country rats eat what they can
It’s been nearly 3,000 years since Aesop wrote “The Town Mouse and the Country Mouse,” the fable in which an urban rodent exposes his rural cousin to the city’s superior dining options. A new study suggests Aesop was right about the geographical differences in rodent diets.
By analyzing the remains of brown rats that lived in and around Toronto between 1790 and 1890, researchers have determined that city rats enjoyed a higher-quality and more stable diet than rural rats did. Just as in Aesop’s tale, the city rats benefited from the largesse of human waste, whereas country rats scraped by.
“Rats that lived in the city had a lot more meat in their diet,” said Eric Guiry, an archaeologist at the University of British Columbia and lead author of the study, which was published recently in Proceedings of the Royal Society B. “You could see the difference in their bones.”
Guiry and his co-author, Michael Buckley of the University of Manchester, are specialists in the emerging field of paleoproteomics, which uses the proteins in ancient bones to glean insights into an animal’s behavior. Guiry wanted to use the technique on rats to see what it could reveal about human populations in the 1800s — a less onerous proposal than digging up and analyzing human remains. Knowledge gained from the research also could help cities better control their rat populations.
“Rats are really interesting, because their diets are a reflection of foods people leave lying around,” Guiry said.
For the current study, the researchers collected rat bones from museums, universities and archaeologists in the Toronto area.
Although it’s not necessarily surprising that city rats eat better than country rats, Guiry is hopeful that his method could be used to shed light on human diets and the density of populations during other, less well-documented eras.
The real challenge, he said, is finding usable remains: “Until recently, archaeologists would find rat bones and just think, ‘Oh, garbage.’”
More urgently, he said, the method could hold promise for studying rat behavior in cities and controlling rat infestations, a task that costs billions of dollars every year.
“This has given us an overview of how rats are eating and behaving over a long period of time in an urban area,” Guiry said. “And food is really important to how they reproduce.”
— Douglas Quenqua
Why Southeast Asia and Australia’s coral reefs became so rich in species
Dive into the coral reefs of Southeast Asia or Australia and you’ll likely spot a wrasse. But which of the hundreds of kinds of wrasses will you see?
These fish can be 1 inch to more than 8 feet in length. Some are somber-colored; others look like they’re attending a rave. Different species have their own creative feeding strategies: humphead wrasses crush shellfish; tubelip wrasses slurp corals and cleaner wrasses act like carwashes, eating parasites and dead tissue off other sea creatures.
This spectacular diversity stems from wrasse ancestors that migrated from the prehistoric Tethys Sea to the area that now bridges the Pacific and Indian oceans. There, in a vast and vibrant cradle of coral reefs, they settled and steadily diversified over tens of millions of years.
Their story fits into a larger pattern. This region, the Central Indo-pacific, has become the hot spot with the most biodiversity in Earth’s oceans because many ancestors of today’s marine life colonized it so long ago, according to a recent paper in Proceedings of the Royal Society B.
The study emphasizes that biodiversity is a long game, and that the richness of species in the world’s oceans will not be easily replaced if it is lost to human activities.
“It has taken tens of millions of years to build the biodiversity of coral reefs, but it may take us only decades to destroy it,” said Mary Wisz, a professor at the World Maritime University in Sweden who was not involved in the study.
Explorers have long wondered why the Central Indo-pacific holds such exceptional bounty, said Elizabeth Miller, a PH.D. candidate studying ecology and evolutionary biology at the University of Arizona and the lead author of the paper.
Using databases that aggregate research done by hundreds of scientists, Miller’s team categorized more than 12,000 fish species as present or absent in eight marine regions around the world.
The researchers then traced living species back in time, using an evolutionary tree, statistics and computer simulations to infer where their ancestors originated and when their lineages might have moved to different places.
Overall, the scientists found, biodiversity in a region today is highly related to the age and number of colonizations it has experienced. The Central Indo-pacific is so diverse largely because many old lineages have settled there.
— Steph Yin
Lurking underwater, a prehistoric wolf in sheep’s clothing
Some 150 million years ago, prehistoric fish swimming in the sponge and coral reefs of what is now southern Germany might not have suspected there was a piranha-like predator prowling among them. But by the time they realized the danger — CHOMP! — the sneaky creature would have bitten off one of their fins.
Back then, these waters were teeming with bony fish called pycnodontiformes, which were known for their crushing teeth that were likely used for smashing snail shells and sea urchin spines. Scientists thought, for the most part, that other fish were not on their menu.
But now, researchers have found a pycnodontiform with razor-sharp teeth that they think ripped chunks of flesh, especially fins, from other fish. They named it Piranhamesodon pinnatomus.
The finding, published recently in the journal Current Biology, represents the earliest record of flesh-eating in bony fish and may cause scientists to rethink the predatory practices of this group.
“It’s a wolf in sheep’s skin,” said Martina Kölbl-ebert, a vertebrate paleontologist and director of the Jura-museum Eichstätt in Germany. “This one had daggers and scissors in the mouth, implying a completely different mode of feeding.”
With scalpels, fine-needles and a microscope, Kölbl-ebert and her colleagues examined the fossil in 2016. It came from the same fossil deposit where scientists first discovered Archaeopteryx, the famous feathered dinosaur.
This area was most likely a shallow tropical sea dotted with small islands inhabited by insects, lizards and dinosaurs when the piranha-like fish was alive, according to Kölbl-ebert. After extracting the fossil from the rocks, they performed a micro-ct scan on the specimen.
Although the Piranhamesodon pinnatomus may have looked like other colorful coral fish from the outside, there were major differences inside its mouth.
Most pycnodonts had front teeth shaped like chisels that they used for grasping, as well as flat, cobble-shaped teeth for crushing. But the new species, just a few inches in length, had six long, pointed knifelike teeth that were slightly curved backward as well as six triangular teeth with serrated edges.
While its pycnodont relatives mostly swallowed their prey whole, the sharp teeth of the newly discovered fish would have allowed it to munch on prey that was much larger than itself.
— Nicholas St. Fleur
Scientists catch rare glimpses of the endangered vaquita
Scientists working to prevent the extinction of an elusive porpoise called the vaquita put out to sea last month, anxious about what they would — or would not —find.
It has been almost two years since the last count of vaquitas, when scientists estimated that only 30 remained in the Gulf of California, their only habitat.
Since then, the illegal fishing that has decimated the species has outpaced law-enforcement efforts. Seven vaquitas have died or been killed, and experts fear that more have been entangled in gill nets and have drowned.
“Every time I go to look for vaquitas, I worry it will be my last time to see them or that we may not even be able to find them,” Barbara Taylor, a biologist at the National Oceanic and Atmospheric Administration, wrote in an email.
She was aboard the ship on Sept. 26 when a mother and calf surfaced at sea, a sight greeted with elation and relief.
Later that day, expedition scientists spotted two more adults. And the following day, at least two additional pairs appeared, including what appeared to be another calf.
The calf sightings were particularly important because they may provide the first evidence that vaquitas can produce one calf annually instead of one every two years, as scientists had believed.
Observers spotted an adult vaquita last year and again this year, identified by distinctive markings on the dorsal fin. Presumably a female, she was accompanied by a calf last year and by a smaller calf this year.
“Calving every year doubles their growth rate and gives more hope for recovery,” Taylor said.
Distinguished by a rounded profile and dark patches around the mouth and lips that give it an almost childlike look, the vaquita was rare to begin with, inhabiting only the upper reaches of the Gulf of California.
The porpoise has long been endangered by curtain-like gill nets set to catch shrimp, sierra and other fish. But it was the illegal trade in a fish called the totoaba that pushed the vaquita to the edge of extinction. Demand in China for the endangered totoaba’s swim bladder, considered to be a delicacy, drives a far-flung criminal network.
Scientists were confident that a few vaquitas survived, because marine acoustic monitors continue to registered the echolocation clicks they make to find food.
— Elisabeth Malkin