Flowering plants are some of nature’s greatest show-offs. Donned with brightly colored petals and evocative scents, many species of flowering plants put a lot of energy into sticking out and attracting the attention of passersby. However, for one species of the plant in East Asia, shying away from unwanted attention has proved to be a more effective survival strategy.
A new study published in the journal Current Biology this week reports that a plant used in traditional Chinese medicine has evolved to become less visible to humans, suggesting humans are driving the species' color change because camouflaged plants have a better chance of survival.
Annually after its fifth year of life, the Fritillaria delavayi typically springs a vivid green flower. However, under the pressure of humans picking the plants for traditional Chinese medicine, some populations of the plant appear to be sticking to its greyish-brown coloring in order to camouflage itself against its rocky surroundings.
"Many plants seem to use camouflage to hide from herbivores that may eat them – but here we see camouflage evolving in response to human collectors," Professor Martin Stevens, study author from the Centre for Ecology and Conservation at the University of Exeter in the UK, said in a statement.
"It's remarkable to see how humans can have such a direct and dramatic impact on the coloration of wild organisms, not just on their survival but on their evolution itself," he added. "It's possible that humans have driven evolution of defensive strategies in other plant species, but surprisingly little research has examined this."
In the new study, scientists at Kunming Institute of Botany in China and the University of Exeter have shown that the level of camouflage in the plants was tightly correlated with how heavily it was being harvested in that area.
Fritillaria delavayi is a perennial herb found in the rocky hillsides of China’s Hengduan mountains. In Nepal and China, the bulb of the plant is traditionally revered for its touted ability to treat coughs and other respiratory diseases. These purported medicinal benefits have seen the plant extensively harvested, especially in recent decades which have seen a spike in demand for the plant's prized bulbs.
To investigate the plant's recent shifts of coloration, the researchers started by speaking to local people about the areas where the plants were most heavily harvested. This revealed that the level of camouflage in the plants was correlated with harvesting levels, with more vibrantly colored plants being found in areas that were harvested less. A computer-based experiment then confirmed that the green plants were significantly easier to spot compared to grey or brown varieties when against the ground.
"Like other camouflaged plants we have studied, we thought the evolution of camouflage of this fritillary had been driven by herbivores, but we didn't find such animals. Then we realized humans could be the reason," said co-author Dr Yang Niu.
Commercial harvesting isn’t the only human-driven selection pressure changing the planet’s plants in a profound way. Another recent study from September found that the UV-absorbing pigmentation of flowers from across the world increased throughout the latter half of the 20th century, most likely as a result of declining ozone in the atmosphere and the rising temperatures linked to climate change.