‘Borrowed’ virus genes put wings on some pea aphids

Wingless (left) and winged (right) pea aphids. (Credit: Omid Saleh Ziabari/U. Rochester)

Scientists have pinpointed genes that influence whether pea aphids produce offspring with or without wings in response to their environment.

For many organisms, cues from the environment influence traits. These features, known as phenotypically plastic traits, are important in allowing an organism to cope with unpredictable environments, researchers say.

In a paper in Current Biology, scientists shed light on how phenotypically plastic traits evolve and address critical questions about the evolution of environmentally sensitive traits.

Pea aphids are insects that reproduce rapidly and typically give birth to offspring that don’t have wings. As many gardeners know, aphids can quickly overwhelm and kill host plants on which they live and feed.

“Aphids have been doing this trick for millions of years.”

When other aphids crowd an environment, females begin producing offspring with wings that can then fly to and colonize new, less crowded plants.

“Aphids have been doing this trick for millions of years,” says Jennifer Brisson, an associate professor of biology at the University of Rochester. “But some aphids are more sensitive to crowding than others. Figuring out why is key to understanding how this textbook example of phenotypic plasticity works.”

The researchers used techniques from evolutionary genetics and molecular biology to identify genes that determine the degree to which aphids respond to crowding.

Surprisingly, the genes they uncovered are from a virus that then became incorporated into the aphid genome and causes its host to produce offspring with wings. Researchers say they believe the virus does this in order to facilitate its own dispersal.

As Brisson and former postdoctoral student Benjamin Parker found, the gene from the virus retained the same function of producing winged offspring even after it transferred and incorporated into the aphid genome.

“This is a novel role for viral genes that are co-opted by the genome for other purposes, like modulating plastic phenotypes,” says Parker, now an assistant professor of microbiology at the University of Tennessee. “Microbial genes can become incorporated into animal genomes, and this process is important to evolution.”

Most laterally transferred DNA—DNA inherited from other organisms, like viruses—is not expressed by its hosts because it is quickly inactivated or eliminated. However, there are examples in most organisms—even humans—where genomes co-opt genes laterally. In humans, for instance, a retrovirus co-opted the gene that creates a membrane between the placenta and the fetus.

Brisson and Parker found a clear case in which the organism’s genome co-opted the genes from outside an organism to modify the strength of a plastic response to environmental cues. Microbial genes like those from viruses can, therefore, play an important role in insect and animal evolution, Brisson says.

“Even in ancient traits like the one studied here, new genes can start to play a role in shaping plastic traits and can help organisms cope with an unpredictable world.”

Source: University of Rochester