iStock
iStock

5 Ways Plants Communicate

iStock
iStock

You may not think of plants as particularly chatty or active organisms, but they’re not as passive as they might seem. Plants can’t run away, so they have to develop other strategies to stay alive, as James Cahill, an environmental plant ecologist at the University of Alberta, explains in “What Plants Talk About,” a documentary from the PBS show NATURE. They’ve evolved the use of chemicals to communicate with insects and each other in order to thrive. Here are five behaviors that show how active plants can be. 

1. Plants can call for help

When you inhale the sweet smell of freshly mown grass or cut flowers, what you’re actually smelling is the plant’s distress call. “It’s the plant's way of crying out for help,” Cahill says. The scent attracts insects that will eat the pests currently munching on their plant-bodies. For instance, the wild tobacco plant can identify a hornworm caterpillar by its saliva. When attacked by this caterpillar, the tobacco plant emits a chemical signal that appeals to the insect’s enemies. Within hours, caterpillar predators like the big-eyed bug show up, ideally driving the pest away. 

2. Plants can eavesdrop

Plants can eavesdrop on the chemical signals of their brethren, and sometimes respond to another plant’s SOS cry by ramping up their own defenses proactively, knowing that a hungry insect is nearby. 2013 review found 48 studies support the idea that plants increase their defenses after their neighbors are damaged. For instance, when wounded by a hornworm, sagebrush releases defensive proteins called trypsin proteinase inhibitors (TPIs), which prevent the insect from digesting protein and stunt its growth. When neighboring plants—even other species—are exposed to the chemical signals of damaged sagebrush, they begin readying their defenses. Wild tobacco, scientists found, begins prepping to make these TPIs when it senses a distress call from sagebrush, giving it a head start on defending itself if the caterpillar comes calling. 

3. Plants can defend their territory 

Plants compete with each other for sunlight, jostling for position among their neighbors. They also can push out competition in other ways. The invasive knapweed plant—native to Eastern Europe but wrecking havoc on U.S. grasslands—has roots that release certain chemicals to help the plant take in nutrients from the soil. Those same chemicals also kill off native grasses. Thus, the knapweed ends up taking over large territories and killing off its competitors, much like some animals do. Some plants, however, have formed a defense. Lupin roots secrete oxalic acid, which forms a protective barrier against the toxic chemicals given off by knapweed. Lupin can even protect other plants in its vicinity from falling prey to the invasive species. 

4. Plants can recognize their siblings 

Plants can sense when other plants are growing around them. This helps them compete for resources like sunlight, growing more if another plant is shading them, for instance. But like animals, they tend to recognize and support their kin. In an experiment with sea rocket, a plant that often grows close together with its siblings, plants that were grown in pots with relatives had more restrained root growth than plants grown with random strangers. The plants in the stranger condition grew more roots in order to better compete for food, whereas the sibling plants were more considerate of each other’s needs. Further experiments showed that sibling plants recognize each other via chemical signals.  

5. Plants can communicate with mammals

Plants go out of their way to attract more than just insects. A carnivorous pitcher plant native to Borneo has evolved to hijack bat communication systems, turning the bats’ echolocation to its advantage. According to a new study in Current Biology, Nepenthes hemsleyan has a concave structure that is specially suited to reflect bat echolocation, helping the bats find the plant. The bats roost in the pitcher plant, and provide important nutrients by way of the bat guano that gets distributed in the soil nearby.   

nextArticle.image_alt|e
iStock
These Sparrows Have Been Singing the Same Songs for 1500 Years
iStock
iStock

Swamp sparrows are creatures of habit—so much so that they’ve been chirping out the same few tunes for more than 1500 years, Science magazine reports.

These findings, published in the journal Nature Communications, resulted from an analysis of the songs of 615 adult male swamp sparrows found in six different areas of the northeastern U.S. Researchers learned that young swamp sparrows pick up these songs from the adults around them and are able to mimic the notes with astounding accuracy.

Here’s what one of their songs sounds like:

“We were able to show that swamp sparrows very rarely make mistakes when they learn their songs, and they don't just learn songs at random; they pick up commoner songs rather than rarer songs,” Robert Lachlan, a biologist at London’s Queen Mary University and the study’s lead author, tells National Geographic.

Put differently, the birds don’t mimic every song their elders crank out. Instead, they memorize the ones they hear most often, and scientists say this form of “conformist bias” was previously thought to be a uniquely human behavior.

Using acoustic analysis software, researchers broke down each individual note of the sparrows’ songs—160 different syllables in total—and discovered that only 2 percent of sparrows deviated from the norm. They then used a statistical method to determine how the songs would have evolved over time. With recordings from 2009 and the 1970s, they were able to estimate that the oldest swamp sparrow songs date back 1537 years on average.

The swamp sparrow’s dedication to accuracy sets the species apart from other songbirds, according to researchers. “Among songbirds, it is clear that some species of birds learn precisely, such as swamp sparrows, while others rarely learn all parts of a demonstrator’s song precisely,” they write.

According to the Audubon Guide to North American Birds, swamp sparrows are similar to other sparrows, like the Lincoln’s sparrow, song sparrow, and chipping sparrow. They’re frequently found in marshes throughout the Northeast and Midwest, as well as much of Canada. They’re known for their piercing call notes and may respond to birders who make loud squeaking sounds in their habitat.

[h/t Science magazine]

nextArticle.image_alt|e
iStock
This Plant Can Burn Your Skin With Its Sap—And It May Be Coming to Your Neighborhood
iStock
iStock

It's huge, it's extremely dangerous, and it's spreading. The giant hogweed (Heracleum mantegazzianum) contains a corrosive sap that causes severe rashes, third-degree burns, and even permanent blindness if you get the photosensitive chemicals on your skin or in your eyes, Science Alert reports.

The noxious, invasive weed was just identified in Clarke County, Virginia, near the Massey Herbarium at Virginia Tech. That brings the number of states it's been spotted in to 11, including Washington, Oregon, Illinois, Michigan, North Carolina, Pennsylvania, New York, Connecticut, Massachusetts, and Maine. Beyond the U.S., it has taken root all over the world, from the UK to Iceland to Australia.

Similar to the common but slightly less dangerous cow parsnip, giant hogweed is native to Central Asia and was first brought to North America in the early 1990s as an ornamental plant, its unique shape making it popular among gardeners. But it soon became invasive: Once it’s established in an area, it can take up to five years to eradicate a colony.

Now the plant is considered a public health concern. Hogweed can cause a reaction known as phytophotodermatitis when it comes into contact with skin that is subsequently exposed to UV rays—but the effects of hogweed are much more severe. A painful blister can develop within hours and last for months; the exposed skin can remain sensitive to sunlight for years even after the blisters heal.

Hogweed can be difficult to distinguish from the cow parsnip, and the plant is often misidentified. First, check for height: Hogweeds are typically taller than 8 feet, while cow parsnip tends to be 5 to 8 feet tall. Hogweed stems are green with purple specks and coarse white hairs, while parsnip stems are green with fine white hairs. For more tips and photos, check out the New York Department of Environmental Conservation’s guide.

If you see a plant you think might be a giant hogweed, take a few photos and send them to your state's department of agriculture to identify—and whatever you do, don't touch it.

[h/t Science Alert]

SECTIONS

arrow
LIVE SMARTER
More from mental floss studios