The Wasps That Tamed Viruses | Science

If you prick the ovary of a wasp called Microplate DestroyerThe viruses burst forth in large numbers, glowing like iridescent blue toothpaste. “It’s beautiful and surprising that there are so many viruses out there,” says Gaelen Burke, an entomologist at the University of Georgia.

m. demolition It is a parasite that lays eggs in caterpillars, and the particles from its ovaries are “domesticated” viruses that have been specially configured to survive harmlessly in the wasps and serve their purposes. The virus particles enter the caterpillar through the wasp’s sting, along with its own eggs. The viruses then inject their contents into the caterpillar’s cells, delivering genes that are different from those of a normal virus. These genes suppress the caterpillar’s immune system and control its development, making it a harmless breeding ground for the wasp’s young.

The insect world is full of parasitic wasp species that eat other insects alive as babies. And for reasons scientists don’t fully understand, they have repeatedly adopted and domesticated wild disease viruses and turned them into biological weapons. Half a dozen examples have already been described, and new research points to many more.

By studying viruses at different stages of domestication, researchers are trying to understand how this process unfolds.

Diversification partners

A typical example of a virus domesticated by a wasp is the group of bracoviruses, which are thought to have evolved from a virus that infected the wasp or its caterpillar host about 100 million years ago. This ancient virus inserted its DNA into the wasp’s genome. It has been part of the wasp ever since, being passed on to each new generation.

Over time, wasps diversified into new species, and their viruses diversified with them. Bracoviruses are now found in about 50,000 wasp species, including m. demolitionOther domesticated viruses originate from different wild viruses that entered wasp genomes at different times.

Researchers debate whether domesticated viruses should be called viruses. “Some say it’s still a virus; others say it’s integrated and part of the wasp,” explains Marcel Dicke, an ecologist at Wageningen University in the Netherlands who described how domesticated viruses indirectly affect plants and other organisms in a 2020 paper in the journal Annual review of entomology.

As the wasp-virus composite evolves, the virus genome spreads throughout the wasp’s DNA. Some genes are disrupted, but a core set remains: those needed to make infectious particles of the original virus. “These pieces are in different places in the wasp’s genome. But they can still communicate with each other. And they continue to make products that interact with each other to make virus particles,” explains Michael Strand, an entomologist at the University of Georgia. But instead of containing the entire viral genome, as a wild virus would, the domesticated virus particles serve as a delivery vehicle for the wasp’s weapon.

These weapons vary widely. Some are proteins, while others are genes on short stretches of DNA. Most bear little resemblance to wasps or viruses, so their origins are unclear. And they are constantly changing, engaged in an evolutionary arms race with the defenses of caterpillars or other hosts.

In many cases, the researchers haven’t yet even discovered what the genes and proteins are doing inside the host wasps, or proven that they act as weapons. But they have uncovered some details.

For example, wasps m. demolition They use bracoviruses to introduce a gene called glc1.8 in immune cells of moth caterpillars. General glc1.8 It causes infected immune cells to produce mucus that prevents them from attaching to wasp eggs. Other Bracovirus Genes m. demolition They cause immune cells to commit suicide, while others prevent the caterpillars from suffocating the parasites in their melanin sheaths.

Wasps remain under control

Taming viruses is likely a dangerous endeavor. After all, the wild relatives of domesticated viruses can be deadly, causing cells to produce viral particles and then explode, releasing their contents. Some of these cause the insects’ insides to dissolve. In fact, even in a domesticated situation, specialized cells in the wasp’s ovaries must sometimes burst to release the viral particles.

“The wasp has to find a way to control this virus so it doesn’t infect and kill the wasp itself,” says Kelsey Coffman, an entomologist at the University of Tennessee.

How did wasps learn to control their pets’ viruses? The most important thing is that they are castrated. The virus particles cannot reproduce because they do not contain the genes that are crucial for creating new virus particles. They remain in the wasp’s genome.

Wasps also control where and when the domesticated virus particles are produced, presumably to reduce the risk of the virus getting out of control. The bracovirus particles are produced in only one cavity of the female’s reproductive system and only for a limited time.

Key viral genes are completely lost, so domesticated viruses cannot replicate their own DNA. This loss is seen even in recently domesticated viruses, suggesting that it is an important first step.

In fact, any viral gene that doesn’t help the wasp will accumulate mutations. So much time has passed in the bracoviruses that unused genes are unrecognizable. Remnants of viruses that were domesticated more recently can still be identified.

The ‘Missing Link’ Has Been Found

There’s nothing special about a genome full of dead viruses. Viruses infiltrate animal genomes all the time; even our own DNA is riddled with their remains. But parasitic wasps are known to retain only entire sets of genes that still work together to make virus particles.

Researchers are eager to understand how this relationship begins. For clues, some are turning to a small orange wasp called Diachasmimorpha longicaudatawhich may be early in the domestication of the poxvirus. The poxvirus is not a true domestic virus because its DNA has not entered the wasp’s genome. Instead, it replicates itself in the wasp’s venom glands.

Like other virus-taming wasps, D. longline It injects virus particles into its host, which in this case is a fruit fly worm. And Coffman and Burke, along with researcher Taylor Harrell, showed that without the poxvirus, most wasp larvae die. But unlike fully domesticated viruses, the poxvirus replicates outside the wasp, producing new virus particles in the worm’s cells. The wasp benefits from the poxvirus, but it doesn’t completely control it.

That weak control may reflect the type of virus the wasps started with, Coffman says. Most domesticated viruses come from types called nudiviruses, which integrate more easily into wasp genomes than poxviruses.

But it’s also possible that the wasps haven’t had time yet. In fact, the wasp-poxvirus association is so new that it appears to be present in only one species of wasp. It’s not even present in another species so similar that Coffman didn’t realize at first that his lab had both.

However, the virus is isolated to certain tissues and only replicates during egg development, which may mean that D. longline You’ve already established some protection. Viruses also seem to lose their ability to transmit without the help of a wasp. “I’ve tried feeding flies a variety of viruses, and they don’t seem to get infected that way,” Coffman says.

The poxvirus system is interesting, Coffman adds, because so little is known about how domestication begins. “We can’t go back in time and know how it all started. But this system is new. “We have a snapshot of what’s missing.” While no one knows exactly why viruses continue to domesticate in parasitic wasps, the researchers suspect it has to do with their lifestyle. Internal parasites live in the guts of their hosts, a dangerous environment that’s actively trying to kill them. From the wasps’ perspective, viruses are like toolkits for solving this very big problem.

The wasp must find a way to control this virus so that it does not infect or kill him.”

Kelsey Coffman, an entomologist at the University of Tennessee.

This idea is supported by research conducted in 2023 that analyzed the genomes of more than 120 species of wasps, ants, and bees. The researchers looked in these genomes for clues about the types of viruses that are commonly domesticated. They inferred the presence of domesticated viruses by finding viral genes that had remained functional throughout evolutionary time. Such preservation would not be expected if the genes did not help the wasps survive or reproduce.

As expected, there was little evidence of domestication of these viruses in non-parasitic insects. The same was true for parasites that develop outside the host’s body, where the immune system cannot attack them. But in parasites that develop inside other insects – so-called endoparasitoids – domesticated viruses appear to be much more common.

“There is a special relationship between viruses and these endoparasitoids,” says Julien Varaldi, an evolutionary biologist at the Université Claude Bernard Lyon 1 in France and one of the study’s authors. “This suggests that these viruses play an important role in the evolution of this lifestyle.”

And with hundreds of thousands of wasp species and countless strains of viruses, there’s a good chance the two will merge. It’s an “evolutionary sandbox of possibilities,” Strand says.

The article was translated by Debbie Ponchner. This article originally appeared on Knows Spanisha non-profit publication dedicated to making scientific knowledge accessible to all.

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