microscopic image of ant
August 11, 2017

Scientists create the first mutant ants using CRISPR

In an attempt to learn more about how ants coordinate to complete tasks, researchers from the Rockefeller University Laboratory of Social Evolution and Behavior altered a gene required to sense the pheromones that the insects use to communicate with each other.

The result, as reported in the latest edition of the journal Cell, is that the ants ability to organize into groups to build tunnels, forage for food and protect the colony from potential threats became compromised, hampering the insects’ social behavior and ability to survive within a colony.

“It was well known that ant language is produced through pheromones, but now we understand a lot more about how pheromones are perceived,” Dr. Daniel Kronauer, head of the laboratory and lead author of the new study, explained in a statement. “The way ants interact is fundamentally different from how solitary organisms interact, and with these findings we know a bit more about the genetic evolution that enabled ants to create structured societies.”

Ants rely upon a  class of pheromones called hydrocarbons to communicate information such as their species, colony and reproductive status. These pheromone signals are detected by a series of porous hairs on their antennae that contain proteins known as odorant receptors, the authors said. These receptors recognize specific chemicals and communicate information to the brain.

Findings suggest odorant receptors play a key role in ant communication

As part of their research, Dr. Kronauer, grad student Sean McKenzie and their colleagues studied a group of ants belonging to the species Ooceraea biroi and found that these ants used a group of odorant receptor genes identified as 9-exon-alpha ORs to detect hydrocarbons. Next, they studied the genomes of related insects to determine where these receptor genes emerged in these ants.

What they discovered was that the gene had undergone a tremendous amount of duplication in a relatively short period of time. While ancestral ants had a maximum of three copies of the gene, the Ooceraea biroi had approximately 180, the researchers said. Furthermore, the expansion of these receptors happened at the same time that complex social behaviors started evolving in the species, indicating that these genes were an essential to ant communication.

The study authors then disrupted a gene known as orco, which is necessary for the function of odorant receptors, using the CRISPR genome modification tool. The challenge, they explained, was convincing the rest of the colony to accept these mutants rather than killing them off when they were larvae. The researchers then observed those that managed to make it to adulthood.

“We noticed a shift in their behavior almost immediately,” said co-author and graduate fellow Waring Trible. While ants typically follow a single-file route by detecting pheromones left by other members of the colony, the modified insects were unable to do so. Furthermore, the ants who lacked odorant receptors experienced changes in the shape of their brains, indicating that odorant receptors are essential to proper brain development in the species.

“Our findings suggest that ants... need functional odorant receptors for the brain to develop correctly,” Trible said, adding that the discovery “points to how crucial sensing odors is to ants, an ability that may be less important in other insects.” Next, the researchers plan to explore the importance of other genes in ant communication, including those linked to the division of labor amongst members of the colony.

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Image credit: Sean K. McKenzie/The Rockefeller University