Fritillaria plants should be easy to detect.
Bright green plants are often alone among the confused turtle that heads the Himalayan and Hengduan mountains in southwest China: easy picks for traditional Chinese herbalists, who ground wild Fritillaria bulbs into a popular cough to treat cough for over 2,000 years. The demand for light bulbs is intense, as about 3,500 are needed to produce just one kilogram of dust, worth about $ 480.
But some Fritillaria are very hard to find, with sharp leaves and stems that are barely distinguishable from the gray or brown rocky bottom. Surprisingly, this camouflage of plants seems to have evolved in response to people. Researchers report on November 20 in Current Biology of Fritillaria delavayi of regions experiencing higher harvest pressure more camouflaged than those in less harvested areas.
The new study "is quite convincing," says Julien Renoult, an evolutionary biologist at the French National Center for Scientific Research in Montpellier who did not participate in the study. "It's a good first step in proving that humans appear to be driving the very rapid evolution of camouflage in this species."
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Camouflaged plants are rare but unpublished, says Yang Niu, a botanist at the Kunming Institute of Botany in China, who studies cryptic coloration in plants. In open areas with little cover, such as mountain tops, mixing can help plants avoid hungry herbivores (SN: 29/04/14). But after five years studying camouflage at Fritillaria, Niu found few bite marks on the leaves and saw no animals eating the plants. “They don’t seem to have natural enemies,” he says.
So Niu, his colleague Hang Sun, and sensory ecologist Martin Stevens of the University of Exeter in England decided to see if humans could be driving the evolution of plant camouflage. If so, the more harvested a particular slope is, the more the plants that live there must be camouflaged.
In an ideal world, to measure harvest pressure “would have accurate measurements of how many plants have been collected over hundreds of years” at various sites, Stevens says. "But that data is virtually non-existent."
Luckily, at seven study sites, local herbalists observed the total weight of bulbs harvested each year between 2014 and 2019. These records provided a measure of contemporary harvest pressure. To estimate further back in time, the researchers assessed the ease of harvest by recording the time it took to dig up bulbs at six of those sites, plus an additional one. On some slopes, the lamps are easily dug, but in others they can be buried under piles of rocks. “Intuitively, areas where it’s easier to harvest should have experienced more harvest pressure” over time, Stevens says.
Both measurements revealed a striking pattern: the more harvested or collectible a site is, the better the color of a plant will match its background, measured by a spectrometer. “The degree of correlation was really compelling for the two metrics we used,” Stevens says.
Both: Y. Niu
Human eyes also had more difficulty seeing camouflaged plants in an online experiment, which suggested that camouflage actually works.
Hiding from view can present some challenges for the plant. Pollinators may have more difficulty finding camouflaged plants and gray and brown coloration may impair photosynthetic activity. Still, despite those potential costs, these F. delavayi show how adaptable plants can be, Steven says. "The appearance of the plants is much more malleable than we might expect."