A new spider family tree tries to untangle the evolution of webs
News and notes about science
Spider webs come in many forms, from the trampoline-like construction of the sheet web spider, to the instantly recognizable filigree of the orb weaver. Orbstyle webs are made by diverse spiders, however, and there are two types, one that’s sticky and one that’s not. Ever since biologists began to sort out how tens of thousands of different species of spiders are related to one another, sketching a large, manylegged family tree, they have wondered: Did spiders evolve to spin the orb web only once? Or multiple times?
It’s an important distinction, and one that scientists who study the evolution of spiders have fiercely debated.
If it evolved only once, then all those who weave it today are descended from a single, common ancestor. But there could have been a very different path of evolution in which different spider lineages independently arrived at the design. A new study published in Current Biology supports this hypothesis for spider and web evolution, using genetic data from 159 spider species to draw a new family tree containing multiple distinct branches of orb-weaving spiders.
In the late 1980s and early ’90s, scientists believed this question was satisfactorily answered, said Gustavo Hormiga, a professor at George Washington University and an author of the paper. Before evolutionary biologists were using DNA sequencing regularly, the consensus was that the two groups that make different versions of the orb web had a common orb-weaving ancestor.
DNA has complicated that picture, however. In the past few years, Hormiga’s lab and others have built detailed family trees by sequencing small sections of spiders’ DNA. To have more points of comparison, the team behind the new paper used a more recently developed approach to compare approximately 2,500 genes.
The resulting spider tree shows a massive network of species whose ancestors began to branch away from each other hundreds of millions of years ago. Because the researchers could draw on so many more genes and species than in previous studies, they are able to state the relationships among spiders with greater confidence than in the past, Hormiga said.
— Veronique Greenwood
Studying ‘sea monkey synchronized swimming’: It’s not so bananas
In 2014, John Dabiri found his research on small crustaceans under the microscope of Tom Coburn, then a Republican senator from Oklahoma who crusaded against government spending. In his government “Wastebook” that year, the senator dismissed Dabiri’s work as the study of “synchronized swimming for sea monkeys.”
But Dabiri, an engineering professor at Stanford University, suspected there was more than could be seen by the naked eye in the movements of small marine creatures. And in a paper published recently in Nature, he offered evidence that they are capable of playing a vital role in mixing up the many layers of the oceans and the minerals they contain. The findings may contribute to a better understanding of this process, which ensures that animals get proper nutrients and also plays an important role in regulating the planet’s climate.
Every night, trillions of sea creatures — whales, jellyfish, swarms of shrimp and plankton — take part in what some call the largest mass migration on the planet. From depths of at least 2,000 feet, they swim to the ocean’s surface, in a wave of animals that propagates as the sun sets around the planet. By daylight, they return below.
No one knows for certain how they know to do this — or why. But this vertical migration — especially the one completed every day by some of the ocean’s smallest creatures — may be making big waves.
“These animals are individually small, and the ocean is enormous,” Dabiri said. “It sort of defies intuition that such small organisms could have a major impact in the oceans.”
Dabiri used tall tanks filled with layers of salt water in a lab. He also used brine shrimp — Coburn’s “sea monkeys.” Although these shrimp do not live in the ocean, his team used them because they are a similar size to plankton or krill and their response to light allows the researchers to trigger vertical migrations on demand, which makes them easier to study.
Dabiri’s team found that a single shrimp swimming upward doesn’t produce much flow, but combined with other shrimp, the mob created a downward jet that rapidly and irreversibly churned the different layers of seawater.
— Joanna Klein
Diamonds in a meteorite may be a lost planet’s fragments
In2008,chunksofspacerock crashed in the deserts of Sudan. Diamonds discovered inside one of the recovered meteorites may have come from a destroyed planet that orbited our sun billions of years ago, scientists now believe. If confirmed, they say, it would be the first time anyone has recovered fragments from one of our solar system’s “lost” planets.
“We have in our hands a piece of a former planet that was spinning around the sun before the end of the formation of today’s solar system,” said Philippe Gillet, a planetary scientist at the Federal Institute of Technology in Lausanne, Switzerland, and an author of the paper that was published in Nature Communications.
Gillet’s colleague Farhang Nabiei made the discovery while taking high-resolution images of a meteorite that had landed in the Nubian Desert in Sudan about a decade ago. The space rock is classified as ureilite, a type of rare meteorite that has embedded within it several different types of minerals.
And inside this one, they found diamonds.
The nano-sized gems were much larger than any meteorite diamond that had been previously found, according to Gillet. They were riddled with tiny imperfections, called inclusions, made of chromite, phosphate and iron-nickel sulfides.
Those flaws made the diamond extraordinary.
“It has a chemistry which has no equivalent in the solar system today, in terms of planets,” Gillet said.
Because of the diamonds’ size and chemistry, Gillet and his team concluded that the diamonds formed under intense pressure, of about 20 giga-pascals, which is close to the pressure seen 400 miles below Earth’s surface where the upper mantle transitions into the lower mantle.
Pressure that high could have been reached only inside a planetary body that was between the sizes of Mercury and Mars, he said.
And because the chemistry of the inclusions did not match what is known on planets in today’s solar system, they think the diamonds came from a protoplanet that existed between 4.54 billion and 4.57 billion years ago. That protoplanet most likely collided with another planet and expelleddebristhatendedupin the asteroid belt, where it wandered for billions of years before plunging to Earth.
— Nicholas St. Fleur
These ants explode, but their nests live to see another day
Outside the kitchen door at the Kuala Belalong Field Studies Center in Brunei, on a number of trees near the balcony, there is a nest of special ants.
They explode.
This colony was studied in depth by scientists who, recently in the journal Zookeys, published an in-depth description of the newly named species, called Colobopsis explodens, including a portion of their genome sequence.
Workers of C. explodens have a distinctive, rather foul talent. When their nest is invaded, they rupture their own abdomens, releasing a sticky, bright yellow fluid laced with toxins on their attackers. Similar to honey bees that die after stinging, the exploded ants do not survive, but their sacrifice can help save the colony.
Since 1935, no new species from the group had been officially named and described.
To do this, ideally one needs to collect members of all the different castes in the colony, from worker to queen, write a detailed description of their appearance, and give the species a Latin name, among other things, said Alice Laciny, a graduate student at the Natural History Museum Vienna who is an author of the new paper.
“We knew they existed, and we did experiments on them,” she said, “but it wasn’t described as an official species yet.”
At 6 a.m., the ants come out of their nest and forage for food until about 6 p.m., the researchers found, although it is not exactly clear yet what they eat. A small squad of workers often stands at the entrances of the colony and touches every ant that comes in or out, apparently monitoring the movements of their sisters. The researchers also introduced a weaver ant, a natural predator of exploding ants, to observe the workers’ explosive response.
When a predator touches a worker, the worker will often rupture, tangling the predator in a gluey mess and eventually poisoning it. This strategy of voluntary self-sacrifice makes evolutionary sense because the ants of the colony are all closely related, and the workers are sterile.
“Their way of taking care of their own genes is to sacrifice themselves so the rest of the colony can survive,” Laciny said.
— Veronique Greenwood