Parasites steal genes to control their hosts’ behavior

A new study led by the RIKEN Center for Biosystems Dynamics Research (BDR) has found that parasites have the ability to control their hosts by using genes they might have acquired through horizontal gene transfer. 

Parasites have a known propensity to influence the actions of their hosts, paving the way for their continued survival and ability to procreate. 

Horsehair worms

One of the most intriguing cases is seen in horsehair worms. These worms initiate their life cycle in water, using water-dwelling insects like mayflies as a means to travel to terrestrial environments. 

Upon reaching land, these worms await ingestion by land insects, such as crickets or mantises. Inside these hosts, the worms not only grow but also alter the insect’s behavior. 

In a fascinating turn of events, a fully grown horsehair worm makes the host insect jump into water, which, while facilitating the worm’s reproduction, often results in the insect’s death.

Focus of the study 

Previous research has hinted at the fact that horsehair worms can modify their host’s intrinsic pathways, driving them towards light, and eventually water. However, the underlying molecular mechanisms that allow these worms to emulate the functionalities of their hosts’ central nervous systems have, up till now, been cloaked in mystery.

Seeking answers, the experts embarked on a journey to study gene expression patterns in a Chordodes horsehair worm at varying phases of its control over a mantis. 

What the researchers learned 

The investigations unveiled certain genes that were dominant when the host was under manipulation. 

By contrast, the brain activity of the mantis remained unchanged, pointing towards the possibility that horsehair worms utilize their own protein structures to control the nervous systems of their hosts.

Delving deeper into the origins of these manipulative genes, the scientists made a startling discovery. 

“Strikingly, many of the horsehair worm genes that could play important roles in manipulating their hosts were very similar to mantid genes, suggesting that they were acquired through horizontal gene transfer,” said lead author Tappei Mishina, a postdoctoral fellow in Genetics at BDR. 

Stealing genes

Horizontal gene transfer, which is not linked to reproduction, allows for a direct transfer of genes between two different organisms. This can lead to swift evolutionary transitions.

Supporting data further strengthened the hypothesis that the Chordodes horsehair worms might have acquired these manipulative traits from mantises. In essence, certain genes within the worms matched those in mantises but were conspicuously absent in other horsehair worm species that didn’t use mantises as hosts. 

Host manipulation 

The team’s conclusion centers around the belief that multiple instances of horizontal gene transfer from various mantis species over evolutionary timelines resulted in the presence of these mimicry genes. These genes, especially those linked to neural activity, light attraction, and day-night cycles, seem to play a pivotal role in host manipulation.

It is well-documented that horizontal gene transfer is crucial for bacteria to develop antibiotic resistance. According to Mishina, the identification of more instances of this phenomenon in multicellular organisms will shed light on its intricate dynamics and, more broadly, on evolutionary strategies. 

“The many cases of horizontal gene transfer that we have found in the hairworm can be a good model for study. Using this model, we hope to identify the mechanisms underlying horizontal gene transfer and advance our understanding of evolutionary adaptation,” he concluded.

The study is published in the journal Current Biology.

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