The science lab is a world of vicious creatures that invade ant brains and turn them into zombies. But the latest research has found that these tiny worms are even more sophisticated, changing the host's behavior based on temperature to maximize their chances of survival.
The goal of parasites is to exploit other species by any means in order to advance their life cycle. Some of the most feared human diseases, such as malaria and sleep sickness, are caused by parasites, but many other plants and animals also have to deal with parasites.
The leech (Dicrocoelium dendriticum) is a flatworm with a complex multi-stage life cycle. At some point in their life cycle, meadow leeches can parasitize in ants' bodies and brains, temporarily turning them into "zombies". You've probably heard of the so-called zombie fungus Cordyceps, which can infect ants and control them, and it's a bit like that, except that no mushrooms explode out of the ants' heads.
The life cycle begins when an ant inadvertently eats a certain tasty snail slime ball that contains the larvae of a leech. This can cause ants to be infected with hundreds of parasites, but only one leech can stand out and go to the ant's brain to parasitize. Other parasites hide in the ant's abdomen.
"Here, there may be hundreds of liver leeches inside the ant's body waiting for the next host to take them away," Brian Lund, co-author of the new study, said in a statement. You could say that it made sacrifices for other leeches. ”
Researchers have observed changes in ant behavior caused by leeches when they reach the ants' brains. The next stage of the parasite's life cycle requires it to be consumed by herbivores such as cattle or sheep. To maximize this possibility, the parasite causes infected ants to crawl onto the top of blades of grass and clutch them with powerful jaws to wait for the herbivores to arrive.
To study the phenomenon in more detail, the researchers laboriously marked the numbering and color markings of hundreds of ants in the Biedstrup forest in Denmark. They can continue to observe these markers to assess whether the parasite's effect on the ants changes with factors such as day hours, humidity, and temperature. One of these factors came to the fore almost immediately.
"We found a clear correlation between temperature and ant behavior. We joked that we found the zombie switch for the ants," Fredensberg said.
For parasites, it is optimal to have the ants at the top of the grass in the morning and evening. But when the sun's rays get too strong, researchers have now discovered that the parasite allows ants to crawl down to avoid the sun's damage.
"It's very clever to have ants hang on the grass at a cool time in the morning and evening, waiting for the cow or deer to eat at that time, and then letting them come down to hide from the sun's rays," Fredensberg said. ”
The parasite's life cycle continues – once the ants release the leeches while the stomach of the new host is digested, they reproduce sexually and eventually lay eggs and are excreted from the body. These eggs are ingested by the snail and subjected to asexual reproduction in the snail until they are expelled in a ball of mucus. The whole cycle starts again.
The question of how leeches control ants' brains remains to be answered, but Fredensberg highlights the impact these host-parasite interactions can have on ecosystems that may be more important than many believe.
The study has been published in the journal Behavioral Ecology.