In the brutal world of insect survival, fruit flies have pulled off an extraordinary heist: stealing genes from bacteria to defend themselves against parasitic wasps that would otherwise turn them into living incubators for baby wasps.
Scientists at the University of California, Berkeley have discovered that several fruit fly species snatched this genetic defense system from bacteria millions of years ago – a rare case of genes jumping between very different organisms that provides new insights into how immune systems evolve.
“It’s a model for understanding how immune systems evolve, including our immune system, which also contains horizontally transferred genes,” says Noah Whiteman, director of UC Berkeley’s Essig Museum of Entomology and senior author of the study.
The research focuses on a particularly grim aspect of insect life. Parasitic wasps inject their eggs into fruit fly larvae, turning the flies into unwilling hosts. Without defenses, up to half of all fruit fly larvae can become surrogate wombs for baby wasps – a lifecycle so gruesome it helped inspire the creature in the 1979 movie “Alien.”
But some fruit flies have evolved a powerful defense. The Berkeley team found that several species carry genes stolen from bacteria that produce toxins lethal to wasp eggs. Even more remarkably, when the researchers inserted one of these stolen genes into common laboratory fruit flies that normally lack this defense, it made them resistant to wasp attacks too.
The gene works by producing a toxic enzyme that floods the fly’s body when wasp eggs are detected, effectively killing them before they can develop. The flies evolved precise control over this borrowed weapon – if expressed in the wrong tissues, the toxin would kill the flies themselves.
“When you’re a poor little fruit fly, how do you deal with these pathogens and parasites that are rapidly evolving to take advantage of you?” Whiteman explains. “One way is to borrow genes from bacteria and viruses because they’re rapidly evolving. It’s an ingenious strategy.”
This genetic theft appears to have happened around 21 million years ago, when an ancestral fruit fly somehow incorporated genes from bacteria into its own DNA. These genes originally came from viruses that infect bacteria, creating a three-way genetic exchange that ultimately benefited the flies.
Rebecca Tarnopol, the study’s lead author, notes that while scientists have long known bacteria frequently swap genes – a process that drives antibiotic resistance – finding such clear evidence of gene transfer in complex animals is much rarer. “This shows that horizontal gene transfer is an underappreciated way that rapid evolution happens in animals,” she says.
The findings could have implications beyond the insect world. Understanding how animals can successfully incorporate foreign genes into their immune systems might help researchers develop new therapeutic approaches for human diseases or find ways to fight parasitic infections.
For now, the researchers are continuing to unravel the complex molecular dance between fly, wasp, and bacterial genes. Each new discovery provides insights into one of evolution’s most remarkable tools – the ability to borrow successful innovations from even drastically different species.
The work was funded by the National Institute of General Medical Sciences and was published last week in the journal Current Biology.
