Plants don’t have eyes, so why can they disguise themselves as their surroundings and other organisms?

Produced by: Science Popularization China

Author: Xie Xingchi (Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences)

Producer: China Science Expo

People have long discovered the phenomenon of camouflage in animals, and have conducted in-depth research and extensive scientific popularization on these phenomena. There are three main purposes for animals to camouflage: first, to reduce the risk of detection and discovery by predators; second, to imitate the form of other creatures to mislead predators; and third, to warn predators that they are not edible by using very conspicuous and warning body colors.

Lichen-covered leaf gecko (Uroplatus sikorae) disguises itself as a tree trunk

(Photo source: Veer Gallery)

Hemeroplanes triptolemus mimics a snake

(Image source: YouTube/Andreas Kay)

Cobalt blue poison dart frog (Dendrobates tinctorius) with warning coloration

(Photo source: Veer Gallery)

But in addition to animals, many plants can also simulate the surrounding environment to camouflage. The camouflage methods used by plants are actually not much different from those used by animals. They also change their own colors and shapes to blend into the background, making it difficult for natural enemies to find them; or they use special patterns to create a false edge effect, making it difficult to expose the real outline.

For example, Lithops pseudotruncatella subsp. has become popular in recent years because of its round pebble-like appearance, and many people will grow a few pots. In fact, this is a typical plant camouflager, and the pebble-like appearance is to avoid insects from discovering and eating them.

Lithops evolved into different species

(Photo source: Veer Gallery)

However, compared to the research on animal camouflage, the research on plant camouflage is very limited, and there are still many areas that need to be studied in depth. One of the most important points is that we need to understand the importance of camouflage ability in plant ecology and evolution. For example, how do plants adapt to different habitats through camouflage? Because different populations of the same species produce different camouflage in different environments, one example is that the corydalis on the gravel beach has a gray-brown appearance, while the corydalis growing in the red sandstone area will turn into the same brick red as the rock.

Corydalis hemidicentra camouflaged in sandstone

(Image source: Reference 2)

The difference between Corydalis semi-pursedus and the aforementioned Lithops is that Lithops camouflages itself by evolving into different subspecies or variants to produce different patterns, while Corydalis semi-pursedus can achieve this mimicry by changing the color of its leaves, rather than relying on evolution - that is, even if it is the same species, Corydalis semi-pursedus in different regions will produce different colors. So the question is, plants don't have eyes, so how do they recognize and simulate the surrounding environment?

A Corydalis semi-purple that has successfully bloomed without being discovered by herbivores

(Image source: Flora of China)

One speculation is that these plants will gradually adapt to the surrounding environment because they have been growing in this environment for a long time. Those plants that do not match the color of the environment will be discovered by insects, and only those plants that match the color of the surrounding will survive. They are not like Lithops that have evolved into multiple species, but rely on random colors for camouflage. This seems to be an unconscious change, because the plants have no idea what the surrounding environment is like.

Scientists sampled some seeds of Corydalis semi-purse and planted them, and provided them with different environments. In these different environments, Corydalis will produce multiple color schemes, including gray, green, reddish brown and khaki, but these four colors may appear in the same environment, so it is possible that only those plants that meet the camouflage color will stay here and continue to grow, and those without camouflage will easily be discovered and eaten by animals.

Color changes of Corydalis semicitrus in simulated environment

(Image source: Reference 2)

Similarly, Fritillaria delavayi, which is distributed on the mountainous gravel beaches in southwest my country, has gradually been harvested by humans due to its unique medicinal value, so it has chosen a more rare evolutionary route. However, compared with other camouflaged plants, researchers have observed no obvious signs of animals eating Fritillaria delavayi after long-term observations in many places. Due to the rich alkaloids in the body, Fritillaria plants have strong chemical defenses, which to a certain extent resist animal feeding. Then, facing the biggest natural enemy - the continuous expansion of human logging, Fritillaria delavayi is increasingly threatened, so they choose invisibility as the direction of evolution.

Initially, the Fritillaria thunbergii bloomed a light yellow flower every year after it grew up, and this color was particularly eye-catching on the gray-brown gravel beach. But as human mining activities intensified, researchers found that in areas where people harvested more, Fritillaria thunbergii tended to bloom gray or brown flowers to minimize the possibility of being discovered. The effect of their camouflage also shows that this strategy is effective - researchers conducted an experiment asking people to find Fritillaria thunbergii in 14 pictures of natural environments. The results confirmed that the individuals with higher camouflage and lower greenness were more difficult to find.

The body color changes of different populations of Fritillaria thunbergii

(Image source: Niu Yang, "Commercial harvesting affects the evolution of camouflage colors of alpine plants")

Not only the half-purse Corydalis and the sand fritillary, scientists have discovered at least a dozen plants with camouflage leaves in southwest China. These plants grow in a poor plateau environment where nutrients are scarce. Animals are eager to find food and will not let go of any plants in front of them. Some plants growing here are forced to evolve and develop multiple color systems to provide camouflage to prevent being discovered by animals.

Saussurea quercifolia camouflaged in driftstone

(Photo credit: Xie Xingchi)

Many creatures in nature, such as Corydalis semi-purse and Fritillaria thunbergii, have been affected by natural enemies or human behavior, and have undergone a series of evolutions to disguise themselves. These methods are adjustments made by biological populations in order to survive after the external environment becomes unfavorable for survival. This is how they can continue to reproduce under difficult conditions.

References:

[1]Endler JA.A predator's view of animal color patterns[J].Evolutionary Biology, 1978,11: 319-364．

[2]Niu Yang et al. Divergence in cryptic leaf color provides local camouflage in an alpine plant.[J]. Proceedings. Biological sciences, 2017, 284(1864): 20171654-20171654.

[3]Niu Yang and Stevens Martin and Sun Hang. Commercial Harvesting Has Driven the Evolution of Camouflage in an Alpine Plant[J]. Current Biology, 2020.

[4]Jacobson Connor et al. Effect of Manual Restraint and Visual Security on Heart Rate in Dyeing Poison Dart Frogs (Dendrobates tinctorius azureus) and Leopard Frogs (Lithobates pipiens)[J]. Journal of Herpetological Medicine and Surgery, 2021, 31(1): 59-63.

[5]Aaron Bauer and Anthony Russell. A systematic review of the genus Uroplatus (Reptilia: Gekkonidae), with comments on its biology[J]. Journal of Natural History, 1989, 23(1): 169-203.

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