The animal world's "Train to Busan", are you scared?

Produced by: Science Popularization China

Author: Bingbingbang (Institute of Zoology, Chinese Academy of Sciences)

Producer: China Science Expo

Are there really zombies? There are no humans, but there are some creatures that have become "zombies". For example, zombie cicadas, zombie frogs, zombie ants, etc. These creatures are infected by certain fungi, and their bodies are invaded by fungi, and they lose their own "consciousness" and become "zombies" controlled by fungi.

How do ants get infected by fungi? Will we humans be infected by these specific fungi and become "zombies"? The answer is revealed at the end of the article!

Parasitism of the ant Campylobacter

(Image source: Wikipedia)

Disaster from the sky: How zombie ants are formed

Take zombie ants as an example. An unlucky ant may just be out foraging on a sunny afternoon. While crawling on a tree, it accidentally gets infected with a specific fungus that infects ants. After that, the fungus begins to multiply and grow in the ant's body, gradually replacing the ant's own cells and tissues. The original ant becomes a puppet with an empty shell but a belly full of fungi.

This is not the most outrageous thing. During the crazy growth of the fungus, the fungus will control the "consciousness" of the ants by producing some enzymes or gases, manipulating the behavior of the puppet ants until the value of the ants is exhausted and they die completely.

A battle of wits and courage: the ultimate tug of war between ants and fungi

So do ants have any countermeasures against this kind of fungal invasion? Or are they powerless to resist and can only let the fungus control them? Recently, Austrian and German scientists have found that there is a very obvious "battle of wits and courage" between fungi and ants.

Ants will promptly help their companions clean the fungi on their bodies, preventing the fungi from multiplying in large numbers in their bodies and preventing the formation of zombie ants. At the same time, the fungi will continue to evolve and become difficult for ants to identify, thus escaping the fate of being cleaned up, which is like the saying "the higher the virtue, the higher the evil."

In this study, a team of Austrian scientists conducted a close study of ant colonies.

The experimental ants infected with the pathogenic green muscardine fungus (hereinafter referred to as "fungus") were kept in an environment with and without fellow ants. In the environment with fellow ants, other ants immediately recognized and responded to the infected individuals, and quickly and effectively removed the infectious particles from the colony members.

Two sets of experimental environment settings, one group of ants was raised in an environment without companion members (left picture), and the other group was raised in an environment with companion members (right picture).

(Image source: Reference [1])

In other words, if these fungi want to completely occupy the body of an ant, they not only need to escape the immune system of a single ant, but also successfully avoid recognition by the immune systems of all the ants in its colony.

However, this process of mutual assistance does not exempt ants from fungal infection. In order to cope with the process of mutual assistance and timely cleaning of fungal particles among ant colonies, the fungus has also undergone fundamental changes. The researchers found that over a period of more than 10 infection cycles, the number of spores (also known as the larvae of the fungus) produced by fungi in an environment with ant companions increased significantly compared to fungi living in an environment without ant companions.

Over time, not only did the fungus become stronger, but surprisingly, the ants also reduced their efforts to remove the fungal particles. In other words, the ants were no longer able to identify and remove the fungal particles as quickly and efficiently. The researchers explained this by saying that the fungus had changed and was no longer easy for the ants to recognize.

Is this really the case? Will the fungi really change as the ants resist? To verify this hypothesis, researchers conducted a comparative analysis of fungi in environments with and without ant companions. The results showed that the fungi in the two environments are indeed no longer the same. In an environment where ants have companions to help clean up, the fungi will gradually reduce their own ergosterol content (a fungus-specific compound that can be recognized by the host) to evade the ants' group social immune clearance.

Cordyceps sinensis is actually a combination of insects and fungi.

(Image source: Wikipedia)

This shows that in this war of aggression and resistance between fungi and ants, both sides are constantly upgrading and becoming stronger. Due to the existence of each other, both fungi and ants have to constantly evolve to increase their chances of success. This also makes us feel the "intelligence" of fungi, as if they have their own thinking and consciousness to deal with the resistance of ants.

Will “zombies” infected by fungi appear?

After talking about the battle of wits and courage between ants and fungi, we finally come to the question that you are most interested in - will this terrible fungus invade humans?

We don't have to worry about this yet. Since the human body is a very complex biological system with a perfect immune system, the current ability of fungi is not enough to invade and control human consciousness. Therefore, at least for now, we are still very safe.

Conclusion

Unexpectedly, under the seemingly inconspicuous body of an insect in nature, there is such a fierce war. Researchers used scientific data to explain to us how the war between fungi and insects is escalating, and also gave us a more objective understanding of the microbial community.

References:

[1] https://www.nature.com/articles/s41559-023-01981-6

Editor: Guo Yaxin