Summary: Understanding how parasites ‘hack’ the brains of their hosts may provide new insights into decision making and behavior.
Imagine a parasite that makes an animal change its habits, guard the parasite’s offspring or even commit suicide. While mind-control may sound like something out of a science fiction movie, the phenomenon is very real — and has spawned a new field, neuro-parasitology. As outlined in an article published in Frontiers in Psychology, understanding how parasites “hack” their host’s nervous system to achieve a particular goal could provide new insights into how animals control their own behavior and make decisions.
“Parasites have evolved, through years of co-evolution with their host, a significant ‘understanding’ of their hosts’ neuro-chemical systems,” explains one of the article’s authors, Professor Frederic Libersat from Ben-Gurion University of the Negev in Israel. “Exploring these highly specific mechanisms could reveal more about neural control of animal behavior.”
The article describes some of the sophisticated, cunning and gruesome ways that various parasites outwit and exploit their insect hosts.
One method is to affect how an insect navigates. The spores of one parasitic fungus, for example, invade an ant’s body, where the fungus grows and consumes the ant’s organs while leaving the vital organs intact. The fungus then releases chemicals that cause the ant to climb a tree and grip a leaf with its mouthparts. After emerging from the ant’s body, the fungus releases spore-filled capsules that explode during their fall, spreading the infectious spores over the ground below. By forcing the ant to climb a tree, the fungus increases the dispersal of the falling spores and the chance of infecting another ant.
Similarly, a parasitic hairworm causes infected crickets to seek out water — where they drown. The cricket’s suicide enables the worms to enter an aquatic environment for reproduction.
In another type of interaction, called “bodyguard manipulation,” the parasite forces the infected insect to guard its young. One such parasite is a wasp, which injects its eggs into a caterpillar by stinging it. Inside the live caterpillar, the eggs hatch into larvae, which feed on the caterpillar’s blood. Eventually, as many as 80 larvae emerge from the caterpillar’s body before forming cocoons to complete their growth into adult wasps.
However, wasp larvae are vulnerable to predators in their cocoons. To scare potential predators away, one or two larvae remain in the caterpillar and control its behavior through an unknown mechanism, so that it acts aggressively towards predators — thereby protecting the cocoons.
These examples shed light on the very old and highly specific relationship between parasites and hosts. But how exactly do these parasites affect their host’s behavior?
Neuro-parasitology is still a young field, and in most cases, researchers do not yet fully understand the mechanisms involved. However, many such parasites produce their effects by releasing compounds that act on the neural circuitry of the host. Identifying and using these compounds in the lab could help scientists to work out how neural circuits control behavior.
“Because neurotoxins are the outcome of one animal’s evolutionary strategy to incapacitate another, they are usually highly effective and specific,” says Libersat.
“Chemical engineers can generate hundreds of potential neurotoxins in the lab, but these are random and often useless, whereas any natural neurotoxin has already passed the ultimate screening test, over millions of years of co-evolution.”
Conn Hastings – Frontiers
The image is adapted from the Frontiers news release.
Original Research: Open access
“Mind Control: How Parasites Manipulate Cognitive Functions in Their Insect Hosts”. Frederic Libersat, Maayan Kaiser and Stav Emanuel.
Frontiers in Psychology. doi:10.3389/fpsyg.2018.00572
Mind Control: How Parasites Manipulate Cognitive Functions in Their Insect Hosts
Neuro-parasitology is an emerging branch of science that deals with parasites that can control the nervous system of the host. It offers the possibility of discovering how one species (the parasite) modifies a particular neural network, and thus particular behaviors, of another species (the host). Such parasite–host interactions, developed over millions of years of evolution, provide unique tools by which one can determine how neuromodulation up-or-down regulates specific behaviors. In some of the most fascinating manipulations, the parasite taps into the host brain neuronal circuities to manipulate hosts cognitive functions. To name just a few examples, some worms induce crickets and other terrestrial insects to commit suicide in water, enabling the exit of the parasite into an aquatic environment favorable to its reproduction. In another example of behavioral manipulation, ants that consumed the secretions of a caterpillar containing dopamine are less likely to move away from the caterpillar and more likely to be aggressive. This benefits the caterpillar for without its ant bodyguards, it is more likely to be predated upon or attacked by parasitic insects that would lay eggs inside its body. Another example is the parasitic wasp, which induces a guarding behavior in its ladybug host in collaboration with a viral mutualist. To exert long-term behavioral manipulation of the host, parasite must secrete compounds that act through secondary messengers and/or directly on genes often modifying gene expression to produce long-lasting effects.