TIME plants

Talking Tomatoes: Sick Plants Warn Their Neighbors

Chatterbox: tomato plants have a lot more to say than you'd think
John Burke; Getty Images Chatterbox: tomato plants have a lot more to say than you'd think

Chemical signaling allows healthy plants to defend themselves when a single neighbor is under attack—a result of communication among species that were always thought to be entirely mute

We tend to think of plants as basically inert—the furniture of the natural world. They don’t move, they don’t make sounds, they don’t seem to respond to anything—at least not very quickly. Grass doesn’t cry when you cut it, flowers don’t scream when they’re picked. But as is often the case, our human-centric view of the world misses quite a lot. Plants are talking to each other all the time. And the language is chemical.

Over the last few decades, a growing stream of papers has reported that different types of plants, from trees to tomatoes, release volatile compounds into the air for the benefit of neighboring plants. These chemical smoke signals come in many varieties, but their purpose seems to be to spread information about one plant’s disease or infestation so other plants can defend themselves. That’s been the general idea anyway, but exactly how plants receive and act on many of these signals is still mysterious. In this week’s Proceedings of the National Academy of Sciences, researchers in Japan offer some explanations, announcing that they’ve identified one such chemical message and traced it all the way from emission to action.

The experimenters looked at tomato plants infested by a common pest, the cutworm caterpillar. To start out, they grew plants in two plastic chambers connected by a tube, with an infested plant in the upwind chamber and an uninfested one downwind. When those downwind plants were later exposed to the cutworm pest, they defended themselves against it better than tomato plants that had not been exposed to a sick neighbor.

The researchers analyzed leaves from exposed and unexposed plants and found that out of the 8,226 compounds identified, only one showed up more frequently in the exposed plants, a substance called HexVic. And indeed, when the researchers fed HexVic to cutworms, it knocked down their survival rate by 17%.

Looking for the source of this protective substance, the scientists fingered a chemical precursor to HexVic among the cocktail of volatiles released by the infested plants. When they wafted it over uninfested plants, the plants began to produce HexVic, suggesting that they were turning the volatile into the caterpillar-killing chemical. A series of other tests confirmed that idea: Uninfested plants don’t have this precursor lying around, and must build their own weapon from the early warning message released by their infested relatives.

It’s an elegant tale, and it may be happening in far more plant species than tomatoes and with far more chemical signals that are still unintelligible to us. For now though, it’s hard not to have at least a little more respect for a type of life that not only communicates but, in its own invisible way, looks after its kin.


TIME animal intelligence

Is Your Toddler as Smart as a Crow? No

Stride on: this brainiac bird has a right to strut
Stephen J. Krasemann; Getty Images Stride on: this brainiac bird has a right to strut

High order ideas like water displacement and tool manufacturing aren't beyond the reach of one very smart bird. The skills of the New Caledonian crow reveal just how complex animal brains can be.

When you think about the brainiacs of the animal world, chances are birds aren’t your first thought. They may be finely honed killing machines, epic world travelers, or beautiful singers. But clever? Not so much, right?

Wrong. Some species of birds, especially in the crow family, are eerily good at logic puzzles involving tools, and this week, a new study in PLOS One from the University of Auckland reveals more about that those remarkable skills. Researchers tested New Caledonian crows with a series of trials inspired by Aesop’s fable “The Crow and the Pitcher,” involving dropping stones into a partly filled pitcher to raise its water level. The birds, it turned out, are as good at some of the tasks as 5-7 year-old children.

New Caledonian crows were already known to be a particularly gifted species when it comes to tools, suggesting an ability to plan ahead and think critically about new situations. They can use a stick to reach a treat that’s out of their reach, for example, something that never seems to occur to most non-human animals. And they don’t just use tools, they create them. In a landmark 2002 experiment, investigators watched as a crow called Betty spontaneously bent a piece of wire into a hook to snag some food. (It was the first time she’d ever encountered wire, but that wasn’t going to keep her from lunch.) For researchers looking to understand how and why tool use evolves, New Caledonian crows are rock stars.

In the new study, the investigators used a set of tasks in which six wild crows had to drop different objects into water-filled tubes to make a floating treat—a cube of meat—rise within reach. The question: Did they understand the principles of water displacement well enough to get the treat?

The first five tasks tested the crows’ understanding that dropping objects into a sand-filled tube doesn’t bring the treat within reach, while dropping them in water does; whether, given the choice between dropping objects that sank or floated, or were solid or porous, they’d figure out which got them the treats fastest; and whether they could recognize that different water levels and tube widths presented better or worse options for getting what they were after.

The final task involved a bit of trickery that even young children don’t always understand. Three water-filled tubes protrude from a table top, but under the table’s surface, two of them are connected by a pipe. A treat in the central tube—which is too narrow for the displacement objects—can be reached only by dropping objects into the tube that’s connected. In one prior study using this task, most eight-year-old children succeeded, but not, in most cases, because they inferred the existence of the secret connector. Rather, they simply learned through experimentation that dropping objects in the connected tube got them to their goal. Eurasian jays given the same task fail, even though they succeed at other tasks involving volume.

The crows flew through the first few tasks easily. They grasped the sand task and the floating versus sinking principles as quickly as 5-7 year-old children do, and, notably, seemed to realize that not all sinking objects are equal; in the porous versus solid task, they favored the solid objects, which displaced more water. Confronted with narrow and wide tubes with more water in the wide tube, they used the one with more water to achieve their goal. But when both had the same amount of water, they usually just kept dropping objects into a given tube until they got a snack, showing no sense that one might get them the treat faster. In the central tube conundrum, they never figured out how to get the treat to come into reach.

These are tantalizing signs that the crows do understand how volume displacement works, but that their understanding is fairly rigid. It may be that the crows focus on the properties of the objects they’re dropping in the water, while tube width and how that affects water level is Greek to them. Their response to the central tube task, in turn, reveals that as with jays, their understanding of the basics of how the world should work, quite useful in more straightforward situations, might fail them when things take an unexpected turn. The study used only a few crows, so there’s plenty more work to be done to confirm and expand on these results. But it’s an interesting glimpse of where the limits of New Caledonian crows’ understanding lies, and is another step along our exploration of the largely unmapped world of the animal mind.


Secrets of the Giant, Ancient, Frozen, Killer Virus

Think this flu virus looks nasty? The giant virus is 20,000 times bigger
Ian Cuming—Getty Images/Ikon Images Think this flu virus looks nasty? The giant virus is 20,000 times bigger

Strange things are slumbering in the permafrost—and some of them are able to wake up

It all started with a tiny chunk of dirt. The sample of 30,000-year-old permafrost, a frozen layer of soil from the Siberian tundra, weighed just a fraction of an ounce. But, as TIME reported on Tuesday, that scrap was carrying within it a surprise worthy of a pulp comic book: a gargantuan virus, the largest known to science, and still, despite having been in suspended animation for millennia, quite deadly. Be grateful that it infects only amoebas, not humans.

That virus, weighing in at 1.5 micrometers, is as big as a small bacterium—huge by viral standards. But the significance of the find goes well beyond that gee-whiz metric. Where one übervirus was there should be more, some of which may not be quite as quiescent as we always assumed.

Permafrost has long been known to be something of an ad hoc museum of Earth’s natural history. It contains methane, for example—produced by the decay of long-ago plants and animals and then covered up by the accumulating ice. It’s a good thing that the gas is locked in place this way since methane is a major contributor to global warming; it’s a very bad thing, however, that the warming that has already occurred is causing so much glacial melt, which releases the methane and only accelerates the climate change process. Intact bodies of hapless mastodons and other long-gone creatures are occasionally released by thaws too—though those discoveries are objects only of scientific delight.

Active viruses, though, had not been reported until this week, in the new study published in the Proceedings of the National Academy of Science. The senior authors of the study, Jean-Michel Claverie and Chantal Abergel of Aix-Marseille University, have a long history of virus hunting. Over the last ten years or so, collecting samples from locations as varied as a water tower, a pond, and the ocean off of Chile, they’ve been involved in the discovery of a number of giant viruses, which had been overlooked in earlier research for the very reason that they are so enormous. Standard procedure for studying viruses involves a filtering step that removes all but the tiniest particles in a sample. So the giants—some up to a thousand times the size of the ordinary viruses and containing more than 2,500 possible genes, compared to just eight in the flu virus—were not recognized until 2003. Claverie, Abergel, and their collaborators have since revealed the existence of several more, though giants viruses are only the merest fraction of total virus diversity.

Then, in 2012, Russian researchers managed a magnificent feat: they revived a flowering campion plant from fruits frozen around 30,000 years ago in Siberian permafrost. That got the French researchers thinking: What else could be revived from the permafrost? Ancient bacterial DNA has been found in permafrost, and viruses frozen there in the last couple hundred years have been revived, but no one had grown one from so long ago, and no one had recovered any giant ones.

The French team thus asked the Russian group for some samples of their permafrost and arranged a straightforward test: Since many giant viruses pose as prey for amoebas, then destroy them from within, they fed the permafrost to amoeba cultures. A preserved virus that was seeing the inside of a living cell for the first time in 30,000 years would probably be only too happy to go straight to work. Sure enough, soon the amoebas were dying. “It’s food poisoning,” in essence, says Abergel. “As soon as the virus comes in and is able to unload its genetic material inside the cell, it’s the end for the amoeba.”

To the team’s surprise, however, when they investigated further, the giant virus laying waste to the amoebas did not belong to any of the species already known to science. It had the rough shape of two giant viruses the French team discovered last year, but had a very different genome and reproductive cycle. And that genome is full of mysteries.

“About 10% of its genome resembles classical viruses,” says Abergel. “But there is more than two-thirds of its genes which are new—completely unknown.” The biodiversity of all giant viruses, she says, “is probably tremendous.” The researchers dubbed this new one Pithovirus sicbericum, after the place it was found.

Even if the new virus proves to do nothing more interesting than sleep in permafrost and kill amoebas, the whole class of giant viruses is sparking a lot of scientific interest. For one thing, researchers believe that they may steal some of their genes from their hosts, more than smaller viruses are capable of. “These large ones,” says microbial ecologist Mya Breitbart of the University of Southern Florida, “offer pretty interesting insight into what’s important for a virus.” Those stolen host genes, in other words, must be helping the super viruses in some way, but how is not exactly clear.

The researchers point out that as permafrost melts, thanks to global warming, it’s possible that many more viruses long held in suspension could be released, and not all of them might confine themselves to attacking amoebas. But humans have been rooting around in the permafrost for some time without ill effects. Eugene Koonin, a senior researcher at the National Center for Biotechnology Information at the National Institutes of Health, who studies the evolution of viruses, says he’s not worried. “Even if—thinking very, very hypothetically—permafrost starts to melt, even in a case like that I do not think that this would be a serious concern,” he says. “There will be other concerns that will be much, much more immediate.” Like that methane that’s been keeping the viruses company in their long sleep, just for starters.

TIME Archaeology

What Ancient Aztecs Shared With Modern New Yorkers

New studies suggest that all cities—big, small, primitive and contemporary—grow in similar ways

There wouldn’t seem to be a whole lot that Coeur d’Alene, Idaho (pop. 44,000) shares with Shanghai, China (pop. 24 million), but size isn’t everything. A new study published in PLoS One now shows that all cities, regardless of age and population, grow in pretty much the same way.

As urban scientists have known for a while, densely packed cities can, in some ways, be a bargain. The more infrastructure you build, the less you need of it per person—having twice the number of people means less than twice as much train track. And the amount of money generated by the city’s economy per capita, like other socioeconomic measures including number of patents produced and violent crimes committed per capita, grows in the other direction. Twice as many people means a GDP that’s more than twice as high as before, more than twice as many patents, more than twice as many crimes.

Recently, a team of investigators who sifted through data on 1,500 ancient towns, villages, and cities that flourished in the Basin of Mexico over the course of 2,000 years sought to determine how long ago these laws of scaling emerged. Since the basin is where Mexico City—one of the most densely populated places in the world—stands today, the site could yield some powerful lessons.

(MORE: Enjoy Old French Wine? How’s 2,500 Years For You?)

Archaeologist and lead author Scott Ortman, a professor of anthropology at University of Colorado, began the work by digging out the data collected by researchers in an epic burst of fieldwork in Mexico in the 1960s and re-examining it. Superficially, the scaling laws seemed to apply. “I got on my computer and opened up the data set,” he recalls, “and I saw mathematical patterns that seemed to correspond to the models.”

It was electrifying, and he, physicist Luis Bettencourt of the Santa Fe Institute, and their other collaborators started to delve into the data in earnest, but they quickly ran up against a problem: figuring out the population of different towns from just the archaeological traces left behind is tough since they could not be sure of the methods earlier investigators used to crunch their numbers, which could cast doubt on any analyses that might be conducted later. So Ortman wound up doing a kind of archaeology of archaeology, painstakingly retabulating the raw data to make sure it stood up.

It did. With their re-examined data set, the team was able to say that the settlements did get denser as they grew in just the way that the models of modern cities suggest, and most likely not because of some quirk of how populations were estimated. This means that some ancient cities might have had more inhabitants than previously thought, and might have been more culturally or technologically sophisticated as well.

(MORE: Road Workers Destroy Ancient Mayan Pyramid)

“What we’re working on is a framework or perspective in which all human societies, past and present, actually work in the same way,” says Ortman. “They appear radically different on the surface due to the scale of coordination that’s involved, but the fundamental processes that create those patterns are the same.”

Just why cities are so productive is easy enough to understand. For all the stresses of urban living, the very proximity of so many other people starts a virtuous cycle.“Your life is a path through a city,” Bettencourt explains. “You go to work, you take your kids to school, you go to the grocery store. ” As you move through that densely populated space, you have more interactions with less effort than you would in the countryside, and the result, on a large scale, is more business deals closed, more inventions produced, more brainstorms that otherwise would have stayed quiet. Yes, the subways screech and the taxis ignore you in the rain, but the payoff—once you get home and dry off—can be considerable.

(MORE: America’s Big Cities Are Inequality Hot Spots)

TIME animals

A Salmon Has a Better GPS Than You Do

A Chinook Salmon in the Rapid River in Idaho, on May 17, 2001.
Bill Schaefer—Getty Images A Chinook Salmon in the Rapid River in Idaho, on May 17, 2001.

New insights on how salmon make the migrations they do

Young animals are capable of some pretty astounding feats of navigation. To a species like ours, whose native sense of direction isn’t much to speak of—have you ever seen a human baby crawl five thousand miles home?—the intercontinental odysseys some critters make seem incomprehensible. Arctic tern chicks take part in the longest migration on Earth—more than ten thousand miles (16,000 km)—almost as soon as they fledge. Soon after hatching, young sea turtles take to the waves and confidently paddle many thousands of miles to feeding grounds. Young Chinook salmon likewise make their way from freshwater hatching grounds to specific feeding areas in the open ocean.

Biologists know that these species are able to sense things that humans can’t, from the Earth’s magnetic field to extremely faint scents, that could help with navigation. But they may also be inheriting some specific knowledge of the paths they have to follow. A paper in this week’s Current Biology reports that young salmon appear to possess an inborn map of the geomagnetic field that can help them get where they need to go.

(MORE: The Mystery of Sloth Poop: One More Reason to Love Science)

The researchers, who are primarily based at Oregon State University, performed a series of experiments with Chinook salmon less than a year old that were born and raised in a hatchery and had not yet taken part in a migration. They placed the salmon in pools surrounded by magnetic coils that they could tune to mimic the Earth’s magnetic field at various points in and around the salmons’ feeding grounds. (Kenneth Lohmann at University of North Carolina, Chapel Hill, who has done similar studies that established that baby sea turtles have inborn maps, is also an author of the paper.)

Exposing the fish to the existing magnetic field did not result in their orienting themselves in any particular way. But when the magnetic field was adjusted to resemble that at the northern-most part of the salmon’s ocean feeding range, the fish oriented themselves facing south. When the southern-most part was mimicked, they turned north.

(MORE: The Dingo Didn’t Eat Your Tasmanian Devil)

It’s unlikely the salmon see themselves as located at a certain point on a map in the way we would. Instead, like other animals with extraordinary navigational skills, they’ve probably evolved to respond with a certain behavior when certain environmental conditions, in this case changes in the magnetic field, occur. Such instinctual U-turns would keep the fish from overshooting the safe range of their feeding area, the researchers say. And once that behavior gets established, it would become evolutionarily fixed: anything that helps keep animals alive long enough to reproduce is not going away. If a similar talent were required of humans, evolution would no doubt find a way to provide it to us too. As it stands, Google Maps and GPS will remain the best we can do to rival the salmon.

(MORE: Lions Are Almost Extinct in West Africa)

TIME endangered species

Why it’s Good (For Someone Else) to Get Eaten By a Lion

Getty Images

When top predators are eliminated, the species they prey on can run amok

Ever since the first herder chased a predator away from his livestock—or away from his family—humans have harbored some natural animosity toward large carnivores. We may be thrilled to see the lions at the zoo, but we’re not so excited about mountain lions in our backyards. Campaigns to save endangered carnivores must constantly struggle with the fact that the people who live and work in the animals’ habitats may be less than interested in forgiving and forgetting than in hunting and trapping.

That’s understandable—but problematic. In many cases, the critters that predators eat (your cat or cousin excepted) are supposed to get eaten—at least if the ecosystem is going to stay in balance and species lower on the food chain aren’t going to run amok. As a new paper in Science illustrates, without the proper number of predators living in the proper places, the natural world can go badly awry, with results that can affect both humans and the species we value and protect.

In their review of many years’ worth of literature on the subject, a team of researchers led by William Ripple, a professor of forest ecosystems and society, at Oregon State University, studied seven key carnivore species: lions, leopards, dingoes, the Eurasian lynx, sea otters, gray wolves, and pumas. When those killers were removed from the ecosystem—whether by overhunting, in the case of the sea otter, which dwindled to near-extinction in the 18th and 19th centuries; or by a 3,400-mi. long (5,500-km) fence that excludes dingoes from prime sheep grazing territory—other species have exploded, sometimes with unanticipated results.

(MORE: Forget the Asian Carp. Here’s a Great Lakes Invasive Species to Worry About)

Americans are experiencing just that kind of downstream effect of predator loss now. As TIME reported in a December cover story, the loss of predators including mountain lions and wolves has caused deer populations to grow. Ripple and his colleagues put a hard number on that fact: in areas that have no wolves, deer populations are six times higher than in places wolves live and dine. Not only do the growing numbers of deer invade gardens and cause car accidents, they also destroy young trees, eating their leaves and bark and restricting the growth of the forests of the future. Research has also shown that overgrazing by deer is linked to declines of butterfly and frog populations, since hungry deer eat the flowering plants that the butterflies rely on and the streambank plants that provide shade to the waters where the frogs live.

In West Africa, a similar cascade effect is playing out, as the loss of lions and leopards no longer keeps olive baboon populations in check. The baboons decimate their own food sources and then take to raiding human crops, to the extent that farming families are increasingly keeping children home from school to guard the fields. And in Australia, areas in which dingoes are suppressed experience increased predation by red foxes, which feast on endangered creatures like the dusky hopping mouse. One study surveyed in the new paper showed that the mouse’s numbers were 40 times higher in areas where dingoes roamed—or at least in the two dingo-rich areas surveyed by the researchers.

(MORE: Europe: Where Dogs and Humans Fell in Love)

Humans don’t do a great job of replacing these top predators once they’ve been pushed out, partly because humans don’t hunt the way other top predators do. “The [animal] predators will typically take the young, the old, and the sick prey, where human hunters will take the strongest, prime-aged animals, typically. So that has ecological effects,” says Ripple.

And even when we don’t actively hunt other predators, we kill them in slower, less direct ways like habitat encroachment and climate change. From the moment human beings appeared on the scene, we have sought to eliminate the deadliest beasts around us. Only now, when we’re closer than ever to achieving that dream, are we realizing what a mistake it’s always been.

(MORE: Falling Stars: Starfish Dying From ‘Disintegrating Disease’)

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