Fruit flies have a new weapon to defend against parasitic wasps

In the relentless battle between parasites and their hosts, nature often finds innovative solutions. Sometimes, however, borrowing proven strategies can trump the invention of new ones.

This principle is exemplified by fruit flies, which have adopted a defense mechanism from bacteria to help them counter predatory wasps. The fascinating discovery highlights the dynamic strategies of evolution.

Parasitic wasps vs. fruit flies

Parasitic wasps present a gruesome threat to fruit flies, as they transform fly larvae into hosts for wasp offspring. In some species, parasitism affects nearly half of all fly larvae, in a process that is eerily reminiscent of the 1979 movie Alien.

To survive this biological invasion, fruit flies have co-opted a bacterial defense mechanism, showcasing a remarkable example of horizontal gene transfer (HGT) in animals.

Horizontal gene transfer, where genes jump between unrelated species, is common among bacteria and viruses. It plays a crucial role in spreading antibiotic resistance among microbes.

However, HGT is considered rare in multicellular organisms, such as insects and humans. This study challenges that notion, and demonstrates how animals might also leverage HGT for rapid adaptation.

Borrowed toxin for defense

Researchers at the University of California, Berkeley, led by Noah Whiteman, have identified a bacterial gene that fruit flies use to fend off parasitic wasps.

This gene encodes a toxin that damages the DNA of wasp eggs, preventing them from developing.

According to Whiteman, the discovery provides a model for understanding how immune systems evolve, including our immune system, which also contains horizontally transferred genes. Whiteman.

The team previously showed that knocking out this gene in Drosophila ananassae resulted in nearly all fly larvae succumbing to wasp predation.

In their latest study, published in the journal Current Biology, they successfully inserted the toxin-encoding gene into Drosophila melanogaster, a different species of fruit fly. This made the genetically modified lab flies resistant to predation by parasitic wasps.

The findings highlight the critical role of HGT in animal survival and adaptation.

Strategies of fruit flies against wasps

“This shows that horizontal gene transfer is an under-appreciated way that rapid evolution happens in animals,” said Rebecca Tarnopol, a UC Berkeley doctoral student and first author of the study.

While HGT is well-recognized in microbes, Tarnopol noted that it might occur more frequently in insects than previously thought.

The toxin gene, dubbed fusionB, originates from a bacteriophage – a virus that infects bacteria. This phage initially passed the gene to bacteria that lived inside aphids.

In turn, the bacteria used the gene to defend aphids against parasitic wasps. Flies, borrowing the same genetic tool, now use it to protect themselves from wasps, creating a fascinating chain of genetic borrowing across different species.

Precision in gene expression

Expressing the toxin gene safely was a key challenge. When Tarnopol initially expressed the gene throughout the fly’s body, all of the flies died.

However, targeting specific immune cells enabled the flies to utilize the toxin effectively without harming themselves. This delicate balance illustrates the complexities of HGT.

“If the gene is expressed in the wrong tissue, the fly is going to die. But if it lands in a favorable location, it can confer an amazing advantage,” noted Whiteman.

Gene transfer and immune defenses

The study reveals that horizontal gene transfer might drive immune defense evolution in animals.

“It gives us a picture of a new kind of dynamism,” said Whiteman, highlighting how even animals with innate immune systems can adapt rapidly by borrowing genes from rapidly-evolving microbes.

This discovery also has implications for human health. Understanding how genes are co-opted and shared could inform therapies to combat parasitic infections, cancer, or other diseases.

By investigating how fruit flies utilize bacterial genes to defend against parasitic wasps, the researchers uncovered valuable insights into the evolutionary processes shaping immune systems in various species.

This research sheds light on the genetic mechanisms that animals may use to adapt and survive against evolving threats.

An ingenious strategy

The fruit flies’ ingenious borrowing of bacterial defenses exemplifies nature’s resourcefulness against relentless wasps and other threats.

This remarkable work sheds light on the hidden role of horizontal gene transfer in animal evolution and offers a glimpse into potential applications for human health.

“When you’re a poor little fruit fly, borrowing genes from rapidly evolving bacteria and viruses is an ingenious strategy,” Whiteman concluded.

The study is published in the journal Current Biology.

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