Praying mantises under the spell of a creepy worm: Researchers report on a parasite that apparently stole genes from its victims in order to manipulate their behavior for its own purposes. The results suggest that the worm has acquired the blueprint of substances that influence nerve functions in praying mantises. Using these active ingredients, the parasite can apparently persuade victims to drown themselves in water so that it can complete its development there. The scientists emphasize that the significance of the discovery lies above all in the new evidence of an extensive exchange of genetic information between higher living beings.
Somehow unsympathetic, but still fascinating: Among the many concepts in nature, some organisms have given rise to parasitism - through various strategies they live at the expense of their victims. In recent years, researchers have uncovered particularly bizarre concepts for some representatives: There are parasites that can use certain mechanisms to induce their victims to behave in ways that serve their reproductive purposes. The so-called horsehair worms (Gordioida) are already known as masters of perfidious manipulation. They are so named because their adult body shape resembles these long, thin structures.
The life cycle of these insect parasites begins in water: There, tiny young animals develop from eggs, which then attach to aquatic insect larvae, from which flying insects such as mayflies develop. Bound to them, the worms can get out of the water to their final hosts. Some species have specialized in praying mantises. When these predatory insects eat a worm-laden mayfly, the parasites enter its intestines. There they can develop into adults. In order to reproduce, they then have to get back into the water. It is already known that the parasites do not leave this to chance: infected praying mantises specifically seek out water into which they then fall. The parasites then leave their victim's body to mate and complete the development cycle.
What underlies the ability to manipulate?
The researchers led by Tappei Mishina from the RIKEN Research Center for Biosystem Dynamics in Kobe have now investigated the question of how the parasite manages to turn its victims into puppets of its reproductive strategy. It was obvious that the worm uses certain strategies to trigger genetic and biochemical processes in its victims that lead to their abnormal behavior. To investigate this, the researchers recorded and compared gene expression patterns in horsehair worms of the genus Chordodes before, during and after manipulating infested praying mantises. At the same time, they examined the genetic activity of the victims.
They identified many genes in the parasites that are regulated in a special way during the time of manipulation. But surprisingly, they found nothing in the victims: gene expression in the brains of the parasitized praying mantises corresponded to that of uninfected ones. As the researchers explain, this shows that the parasite does not trigger substance production in the victims, but rather produces an active ingredient that can influence the praying mantis' nervous system. They suspect that it is a substance that increases reactions to light stimuli. As a result, the insects could be increasingly attracted to the reflections of the water, according to the explanation.
Production of active ingredients through gene stealing
The most astonishing finding, however, came from a database search in order to characterize the genes differentially regulated in the parasites in more detail. “We found that many of the horsehair worm genes, which appear to play an important role in manipulating their hosts, were in turn very similar to genes from praying mantises,” says Mishina. As the team also discovered, these approximately 1,400 genes are not present in the genome of other worms. “This now suggests that the parasites acquired them from their victims through horizontal gene transfer,” says Mishina. This is a biological process in which genes are transferred from one organism to another, but not through reproduction. This form of transmission is primarily known from bacteria. But cases of horizontal gene transfer in higher life forms have also been documented.
If the researchers' results are further confirmed, the current case would involve a very extensive transfer of genetic genes. Mishina concludes: “These presumably repeated cases of horizontal gene transfer now emerging in horsehair worms could provide a model for further studies. “With this model, we hope to identify the mechanisms underlying horizontal gene transfer, which could ultimately improve our understanding of evolutionary adaptation,” said the scientist.
Source: RIKEN Center for Biosystems Dynamics Research, specialist article: Current Biology, doi: 10.1016/j.cub.2023.09.052