An annoying clover may hold secrets to urban evolution
News and notes about science
It’s considered a nuisance or a weed when it pops up in luscious suburban lawns.
But in other places, white clover has become a plant that marvels. It is one of the most rapidly evolving species of flora, learning quickly how to survive in the toughest of urban environments.
According to a study published recently in the Proceedings of the Royal Society B, white clover (Trifolium repens) adapts equally well to cities of all sizes — with 20 studied in Ontario, Canada, from London, with a population near 400,000 to tiny Everett, population 1,670. Researchers had previously explored cities as large as New York, and now they are expanding their explorations to more than 180 cities across the world, in an effort called the Global Urban Evolution Project or GLUE.
Cities work as great natural test cases for evolution, said Marc Johnson, director of the Centre for Urban Environments at the University of Toronto, Mississauga, who led the research. “In many ways it’s an unplanned experiment happening throughout the world over and over again,” he said.
With climate change advancing and more than half the world’s population living in cities — a figure expected to jump to 70 percent by 2050 — Johnson said it would be crucial for scientists to figure out how human encroachment and activity affect the plants and animals that surround us.
The clover adapts to colder climates by losing its ability to make hydrogen cyanide or HCN, a toxin the plant produces to protect itself from predators, like snails, insects and voles, and in the country, cows, sheep and goats. The number of plants that produce hydrogen cyanide increases with every mile away from the city center, the study found, with small cities showing the same effect as big ones.
White clover that grew in an urban environment was less likely to make hydrogen cyanide, Johnson said. Although cities can be warmer than the countryside, the heat and human activity result in less snow than in rural areas. Without snow to insulate the plants from the cold, the clover would poison itself if it could not give up its ability to make hydrogen cyanide, Johnson said.
Since Darwin, researchers have identified three main forces behind evolution: Natural selection, genetic drift and gene flow. This study, Johnson said, shows that natural selection, where some species evolve and are better able to reproduce more than others, is the dominant evolutionary force for urban white clover.
— Karen Weintraub
Worker ants: You could have been queens
The critical factor for determining which ants become queens or workers may be as simple as some extra insulin.
In a study published recently in the journal Science, researchers showed that the genes behind insulin signaling appear to play a key role in distinguishing the ants’ assignments.
In some ant species, a queen can be quite larger and live 20 times longer than a worker, even though they are genetically identical. A number of insect species, including ants, wasps and bees, have queens that are responsible for reproduction, while a far larger number of often-sterile workers forage for food.
“We were interested in where these differences come from, how they’re regulated and how they evolved,” said Daniel Kronauer, the paper’s senior author and an evolutionary biologist at Rockefeller University in New York.
By looking at which genes are activated in the brains of queens and workers of different ant species, Kronauer and his colleagues determined that a hormone called insulin-peptide 2, or ILP2, played the most important role. But other insulin-signaling and unrelated genes were also differently activated, Kronauer said.
“Insulin signaling — and this ILP2 version of insulin — seems to be at the core of these queen-worker differences,” Kronauer said.
In one species, the clonal raider ant, Ooceraea biroi, the team added this hormone to worker ants and activated their ovaries. This suggests that an extra dose of insulin may make the difference between foraging for food like a worker or laying eggs like a queen.
During development, the larvae that are destined to become queens eat more than the ones destined to become workers, which at least partially explains their higher levels of insulinlike peptides, Kronauer said.
Ant ancestors developed the queen-worker social structure because it provided an evolutionary advantage. The new study suggests that insulin signaling could have driven that evolution.
There are 14,000 species of ants, all of which are believed to share the same mechanism of differentiation between queens and workers.
— Karen Weintraub
Think that’s algae swirling beachside? Try green worms
Between April and September, just minutes after waves splash over beaches along the eastern Atlantic coast of England, Wales, France or the Channel Islands, tiny, green worms emerge from their sandy hideouts. They gather in small pools, often near small boulders.
This is Symsagittifera roscoffensis, the plant-worm. Some call it “mint-sauce” because of its vibrant color. And if you happened to be walking where they emerge just after high tide on a sunny day, you would probably think they were algae.
But if you stuck around and watched patiently, you would see something strange happen.
One by one, the worms accumulate, getting denser until a swirling mass forms, just more than 1 inch wide. Movement stops. The pools start drying up. And up to 1 million worms, collected as one, become a verdurous mat, bathing like a beach blanket beneath the sun. When the tide returns, the worms retreat back into the sand.
“They’re really quite fascinating,” said Ana Sendova-franks, a biologist who is studying the worms and collective behavior (usually in ants) at the University of the West of England, Bristol. “I suppose when people stumble across them, they don’t recognize them as what they are.”
Since the late 19th century, this peculiar marine flatworm, just about the size of a pencil tip, has intrigued scientists. They have studied it to understand regeneration, photosymbiosis and climate change. But the plant-worm’s collective behavior has only recently captivated scientists like Sendova-franks.
At first glance, it looks and acts like a plant. But it has a rudimentary brain and nervous system, and if you chop off its head, it rejuvenates. It also has gravity sensors and eyelike photoreceptors. As a juvenile, the worm swallows solar-powered algae that lose their cell walls, eyes (yes, the algae have eyespots) and wiggly tails.
The algae gets incorporated into the worm’s body, between its skin and muscles, and becomes the source of all the nutrients it needs to stay alive. Like corals that host their own algae, the worms bleach in acidic environments, expelling their algae and dying.
— Joanna Klein
Getting a look at the sun when it was in its ‘terrible 2s’
Much like a toddler throwing a tantrum, the sun was exceptionally explosive early in its life. It kicked and screamed with ferocious flares and rambunctious bursts of radiation that were much more energetic than what we see today.
Astronomers believed the sun went through something like the “terrible 2s” based on observations of young stars far away in space.
But they lacked physical clues of what our star was like in the early years after it formed some 4.6 billion years ago.
Now, by studying blue crystals trapped inside a meteorite that predates the planets, researchers have collected what they say is the first direct evidence of the sun’s activity during its fiery start. The findings were published recently in the journal Nature Astronomy.
“This is essentially a real record of the early active sun,” said Philipp Heck, a cosmochemist at the Field Museum in Chicago and the University of Chicago, and an author of the paper.
The researchers studied the Murchison meteorite, which had crashed in Australia in 1969. Embedded inside it were microscopic blue space crystals, called hibonites, which are thought to be among the first minerals that formed in the solar system.
“Since its fall, it has been a treasure trove for science because it contains so much unaltered material from the very early solar system, like these hibonites,” Heck said.
The sun during that period was surrounded by a rotating disc of dust and gas that would eventually birth the planets. The center region of the disk was very hot, about 2,700 degrees Fahrenheit, making that area about three times as hot as Venus, the hottest planet in the solar system.
The hibonites formed in space rocks as the disc cooled. And these rocks were located farther from the sun than Earth is today, according to Heck.
Although the age of the blue hibonites in the Murchison meteorite has not been directly determined, their composition suggests they may have been present during a period that stretches from when the sun was as young as a few hundreds of thousands of years old to as old as about 50 million years, when Earth formed.
The sun is now about halfway through its life cycle. That means that humanity can look forward to another 4 billion years of relative calm as long as we stick around this solar system.
— Nicholas St. Fleur