Queen ants spend most of their time having babies. To rule in a colony, they emit a special scent, or pheromone, on the waxy surface of their bodies that suppresses ovarian development in their sisters, turning the latter into reproductively inactive workers who find food, nurse the young, and protect the colony.
Now, researchers at the University of California, Riverside have begun to unravel the molecular mechanisms behind how ants sense these pheromones and how they control reproduction regulation and other social activities in ant communities. The study, published today in the journal nature communication, highlights how ants use olfactory receptors to distinguish between colony members so they can work together in a complex, hierarchical society. The findings could help develop new pest management strategies.
The research team led by Anandasankar Ray, associate professor in the Department of Molecular Cell Systems Biology, has identified and characterized more than 20 receptors found on the antennae of worker ants that play a role in the division of labor within colonies. Among these is a receptor that specifically responds to a pheromone produced by queen ants, an interaction that ultimately results in a physiological change in the workers’ ovaries.
Ants are eusocial insects, meaning they live in cooperative groups where a female and multiple males are involved in reproduction, and non-breeding individuals play specialized roles such as caring for the young, finding food, and fending off enemies. . Scientists have been interested in how ants communicate for years, which is mediated by a group of hydrocarbon monoxides that ants produce and “wear” like a coat on their bodies. These pheromones allow ants to distinguish between nestmates and non-nestmates and recognize different castes within the same colony.
The effort to unravel the molecular mechanism behind ant odor took several years and a consortium of collaborators from several universities. In 2015, Ray’s group developed a powerful electrophysiological technique in the Camponotus ant species and showed that sensory neurons in small hair-like structures on the ant antennae respond to a variety of different ant pheromones with high specificity. With Ray’s help, this method was set up and tested at Arizona State University in another ant species, the Harpegnathos saltator. Until now, however, the olfactory receptors responsible for detecting these carbohydrate monones had not been identified in any species.
In the current paper, Ray’s group identified and characterized 22 odor receptors that interact specifically with hydrocarbon pheromone produced by other ants, including one — called HsOr263 — that responds to the queen pheromone. These receptors belong to a subfamily of the odor receptor gene family, the 9-exon subfamily.
“We first explored the 9-exon subfamily of olfactory receptor genes, because it’s highly expanded in ants and other eusocial insects, making it a good place to look for receptors that respond to the carbohydrate momons,” Ray said.
Speeding up this research and paving the way for identifying other ant receptors was a technique developed in 2014 by Ray and Gregory Pask, a former postdoctoral associate in Ray’s lab, to express ant olfactory receptors in a genetically modified Drosophila melanogaster fly. . Pask placed the DNA of ant receptors in the fly genome and used genetics to express the ant receptor in fly antennae.
“Once we expressed an ant receptor in the fly antenna, I was able to directly measure the response to individual hydrocarbons at that receptor one at a time,” said Pask, lead author of the Nature Communications paper and currently an assistant professor at Bucknell University in Lewisburg, Pennsylvania. “Using this method, we then identified odor receptors for several important hydrocarbons, including those on workers, males or queens.”
“Ants and other social insects use a mix of hydrocarbons on their bodies as ‘biological barcodes’ that relay important social information within the colony. Our research sheds light on how these ‘barcode readers’ work at the molecular level,” Pask said.
Ray said the identification of ant olfactory receptors provides new insight into the chemical communication systems used by eusocial insects, and future research would explore how these receptors cause physiological changes, such as the suppression of reproduction.
“Ants’ sense of smell and the way smell is processed is a fascinating area of neuroscience, but this work also has future practical applications. By expanding our understanding of pheromone-mediated communication, we have great potential to manipulate insect behavior and control, which will lead to new pest management strategies,” Ray said.