Acacia trees and giraffes

Amid beautiful nature, there is a cold law: if a species cannot adapt to the complex and changing natural environment in time, it will be ruthlessly eliminated.

This law is an extrinsic factor in the evolution of many species on earth. For example, plants evolve various defense mechanisms to avoid being eaten by animals, while animals that feed on plants have to co-evolve with them to survive and reproduce, thus breaking their defenses.

Acacia trees and giraffes are typical examples, on the one hand, dealing with giraffes, acacia trees can be described as a strange trick, on the other hand, giraffes can be said to see the trick, in the road of evolution, acacia trees and giraffes back and forth, a fight is a million years.

Acacia trees are a common plant in the African grasslands, in the long evolutionary road, acacia trees only use the "grow taller" trick to make most phytophagous animals "sigh", but this trick is not effective for giraffes, because they have evolved high enough They have evolved to become the tallest animal on the planet.

Acacia trees have also evolved a "long thorns" defense strategy, their branches are full of sharp, hard thorns, and their length can generally reach more than 10 cm, but this is still ineffective for giraffes because they have evolved long enough, and flexible enough tongue.

Giraffes' tongues can reach a length of more than 40 cm. Usually, they only need to use their flexible tongues to avoid the hard thorns of acacia trees and then gently roll them to eat the leaves.

In addition to physical defense, acacia trees have also evolved a chemical-based trick, that is, the secretion of a chemical called "tannic acid" in the leaves, this substance is toxic to animals, less will make the animal dizzy, and more may cause the animal to die.

However, this trick is still ineffective for giraffes, there are two main reasons for this, one reason is that giraffes in the long gnawing acacia process, have evolved a certain degree of resistance to "tannic acid".

The other reason is that acacia trees can not keep the concentration of "tannic acid" in the leaves at a high level, only when they are nibbled, the concentration of "tannic acid" in the leaves will be significantly increased, and there is a time difference, and the wise giraffes are aware of this They will use the "time gap" to nibble back and forth between multiple acacia trees, thus avoiding eating leaves with too high a concentration of "tannic acid".

For example, there are three acacia trees, "A", "B" and "C", when the giraffe eats "A" When giraffes eat the leaves of "A" if they feel that the taste is not right ("tannic acid" concentration increased), they will stop nibbling and go to eat "B", eat the leaves of "B" taste When the leaves of "B" taste wrong, they will go to eat "C" again, and when the leaves of "C" also taste wrong, the "tannic acid" concentration in the leaves of "A" has dropped. "concentration has dropped, at this time they can come back to continue to eat "A" of the leaves.

To deal with the giraffe's "back and forth eating", acacia trees have evolved a strange trick: when a certain acacia tree is nibbled, it will not only let its leaves in the "tannic acid" concentration be greatly increased, but also release a kind of ethylene pheromone, and it Nearby acacia trees in the sense of this pheromone, will also greatly enhance their leaves in the "tannic acid" concentration so that you can achieve the effect of the "watchful eye" between the trees.

However, giraffes can still see the trick, because they have learned to nibble the next acacia tree in the direction of the headwind, after all, the release of pheromones needs to be transmitted through the air, which means that the acacia tree located in the direction of the headwind can not receive timely notification of "companions".

It is worth mentioning that one "whistling acacia" has evolved a hollow sphere structure at the lower end of its hard spines, which also secretes nectar, thus attracting a large number of ants to stay there.

When the "whistling acacia tree" by animals, these ants living in the tree will be regarded as a threat and launched a fierce attack on it, some ants will even spray a strong corrosive effect of antacid, so that the "gnawers" suffer.

However, for giraffes, this trick is not very useful, because there is a time gap between "ants are alarmed" and "ants attack". Generally speaking, they will leave calmly before the ants start their attack.

To describe it more vividly, the above description uses some anthropomorphic expressions, from our human point of view, "the acacia tree makes strange moves, the giraffe sees the moves" looks very interesting, but in essence, the acacia tree and the giraffe's back and forth is a cruel game of survival between these two species. It is the result of their co-evolution over millions of years.