This in-demand plant is evolving to hide from its predator—humans

The small herb, once easily spotted by its vibrant flower and leaves, is growing brown and grey in spots where humans often pluck them.

Published 9 Feb 2021, 12:43 GMT

In southwest China, high in the Hengduan Mountains, a small herb is getting harder to find.

Called Fritillaria delavayi, it grows three to five bright green leaves and a short stem; once a year, it produces a bright, tulip-shaped, yellow-hued flower. But that eye-catching yellow flower and those vibrant green leaves have started to grow grey and brown in this Fritillaria species. Scientists suspect the plant is genetically evolving drabber parts to hide from its main predator—humans.

In a study published in the journal Current Biology, scientists from China and the U.K. found that in areas where Fritillaria delavayi was being harvested at high rates, the herb was more likely to camouflage.

In regions frequented by fritillaria harvester, plants are more commonly growing with gray, brown-colored leaves, stems, and flowers that blend into their surrounding terrain.

While some plant species grow smaller when overharvested—because their larger counterparts are picked before they can reproduce—this herb, used in Chinese traditional medicine to treat lung conditions like bronchitis or a bad cough, may be the first example of a threatened plant evolving to blend into its surroundings.

A flower in demand

Fritillaria delavayi has been picked and used medicinally for at least 2,000 years, but steadily increasing demand and insufficient supply has triggered a treasure hunt for more. The price for one kilogram (2.2 pounds) of the plant’s bulbs—the part of the plant used medicinally—is around £350. Each tiny bulb is about the size of a thumbnail; to harvest one kilogram requires more than 3,500 individual plants.

Some species of Fritillaria can be farmed, but delavayi grows naturally in high elevations in cold, dry air, conditions difficult for farmers to replicate, and consumers think the wild varieties are better, though there’s no evidence to show that’s true, according to Yang Niu, one of the study’s authors.

In 2011, he and a group of scientists set out to study how the plant was pollinated, curious about why some flowers seemed to be male one year, but both male and female in other years. Their research failed after the plants they tagged in the wild were later dug up and presumably sold, leaving them without study subjects.

Niu and his colleagues previously studied plants that adapted camouflage to hide from herbivores, and had been intrigued by the Chinese herb, a bright plant not known to be eaten by animals. “We then realised that the harvesting...could be a strong selective force,” Niu says over email.

How does it work?

To test this theory, the researchers first consulted with local herbalists who had six years of records showing where plants had grown and how many had been picked. They determined which areas were already heavily harvested and easier to access—versus those tucked away in rocky, mountainous terrains. Using a tool called a spectrometer, which measures wavelengths of light to determine colour, they measured plant colour at different locations and found a correlation between how much of the population had been dug up in a given spot and the colour of a flower.

In less accessible regions where few humans went, plants were still bright green and yellow, but in locations where bulbs were picked in high numbers, colours were growing duller. Delavayi is the only Fritillaria species that grows at high elevations.

The researchers even created a game, “Spot the Plant,” to test how easily camouflaged plants could be found. When volunteers were asked to identify Fritillaria delavayi among rocks and dirt, it took them longer to locate specimens with measurably less vibrant colour.

“It’s a pretty cool, groundbreaking paper,” says Matthew Rubin, an evolutionary biologist at the Danforth Plant Science Centre in St. Louis, Missouri, who was not involved with this research.

“We’ve known that for thousands of years humans have shaped the way plants look through domestication, the way we breed plants for food,” Rubin adds. “This is a really great example of human-mediated selection in the wild, documenting a change and pretty convincingly relating that change to a human pressure, in this case harvesting.”

While it’s common for humans to prompt plant adaption indirectly—changing the environment, for example, and thus prompting adaption—this presents a rarer, direct human-to-plant relationship.

Jill Anderson, a biologist at the University of Georgia, sees the paper’s conclusion as a “tantalising hypothesis,” but says for her to be convinced that it’s humans causing this camouflage, she’ll need to see further proof.

While the paper’s authors ruled out herbivores like yaks as the culprits behind the plant’s change of outfit, Anderson wonders if climatic shifts like stronger UV light at higher elevations may have influenced the plant’s colour.

“Certainly there might be other things contributing to this change—weather or elevation, or an herbivore they didn’t happen to see,” says Rubin. “But the relationship [between harvest pressure and colour] was quite strong—the populations with strong harvest pressure had the closest match to the background.”

Making a natural selection

But say the humans are the agents of change: How would harvesting these bulbs lead the plant to turn brown?

“Humans go into a population and harvest the most visible plants they can find,” says Anderson. “[Harvested plants] no longer have the capacity to contribute to the next generation, whereas the camouflaged plants can live out their life cycles. It’s a process of natural selection in these populations.”

It’s possible Fritillaria delavayi could have evolved in a short timeframe. The plant takes five years to reproduce, meaning all the bright green plants could be picked before they have the chance to pass on their colourful genes. Within a generation or two, a population of plants in a highly trafficked area might have a gene pool with predominantly grey and brown DNA, though scientists didn’t perform a genetic analysis of this plant.

Humans have been known to influence other species. Anderson says in her classes, she highlights the shrinking size of some fish, like Atlantic cod and pink salmon, that are heavily targeted by fishers. As they’re gathered in nets, smaller ones are able to slip through, while the larger ones stay stuck inside. Over time, the population as a whole becomes smaller.

“They took a concept we’ve thought a lot about in animal systems,” says Anderson, “and applied it to plants. This is the first paper I’ve read that explicitly considered how human harvesting can influence a key trait like colouration.”

There are other documented examples of humans influencing a plant’s traits over time. Snow lotus, another threatened Chinese plant, is about four inches shorter than it was a century ago in regions where it’s commonly harvested. In the past century, American ginseng growing in the eastern U.S. has also grown shorter and produced smaller leaves.

Niu says the Chinese government is currently working on updating Fritillaria delavayi’s conservation status to reflect the increasing threat and possibly afford it stronger protections. It’s unclear how large the current population of the species is, but recent surveys show its status in the wild may be declining.

“Just the fact that this is documented is a great first start,” says Rubin.

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