The queen’s genes determine the sex of entire ant colonies

Researchers have discovered the genetic basis for a quirk of the animal kingdom — how queen ants produce broods that are either all-male or female.

Formica ants examining equipment intended to study their habitat. (Alan Brelsford/UCR)

“It’s weird to have a parent who only produces one sex or the other,” says UC Riverside entomologist and study author Jessica Purcell.

Scientists have known for some time that ant colonies can specialize in producing all-male or all-female offspring. For the first time, UC Riverside scientists have located a set of genes associated with this phenomenon on a single chromosome.

Their discovery is described in a new paper published by the Proceedings of the National Academy of Sciences.

When humans mate, both parents contribute one copy of the genome to their offspring. However, female ants are the only ones to carry two specimens like humans and most other animals while the males only carry one specimen.

“Male ants develop from unfertilized eggs that their mothers lay,” says UCR evolutionary biologist and senior study author Alan Brelsford. “That’s why male ants, like bees and wasps, genetically have a mother but no father.”

Purcell and Brelsford found their study specimens in 2016 during a trip to collect and study ants from Riverside to the Arctic Circle. In the Yukon region of northern Canada, they found more than 100 colonies of two Formica ant species that seemed ready for their annual breeding flights. Back in Riverside, doctoral student of ecology German Lagunas-Robles analyzed the genomes of these ants, looking for differences between male and female colonies.

formica ant

formica ant

During mating flights, a queen will mate, land, chew off her own wings and find a place to burrow. She will lay about a dozen eggs in that burrow, which then develop into her first brood of workers. These worker ants are always female, but they will not reproduce. Once mature, the worker bees take over foraging for food and the queen continues to reproduce, laying hundreds of eggs a day.

While the males live only a few hours after their mating flight, the queen will store their sperm and be able to use it over the next decade to produce new offspring. The majority of the fry in an ant colony are wingless workers, but in adult colonies queens will also produce offspring that can fly.

Although the researchers found genes linked to the sex of offspring, genetics may not be the only way queens can influence the sex of their colonies. They could decide not to use their stored sperm, which would result in male ants. Workers could also manipulate a colony’s sex ratio by not feeding or selectively killing certain larvae.

Other studies have shown that food availability also has an effect on the sex of an ant colony. “When extra food is dumped on a colony, it produces fewer males,” Brelsford said. The research team wants to conduct additional research to find out when genes or environmental factors play a greater role in determining the sex of offspring.

The team also wants to investigate how these genes work in different environments. Such details may ultimately help preserve beneficial native North American ants. Mating flights tend to coincide with specific seasons and temperatures. Climate change can affect food availability, the timing of reproduction and generally unbalance a population’s sex ratio.

Unlike their invasive, non-native pesky relatives, these species rarely harass humans and perform important environmental functions.

“Ants are really an integral part of ecosystems as one of the most abundant insects,” Purcell said. “Gardeners love earthworms, but ants do similar things to improve soil health.”

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