How do some ants end up atop the colony's social hierarchy?

An ant's parents appear to play a key role in determining whether the insect will develop into a queen or a common worker, according to a new paper in the journal Science. Some male/queen combinations appear to have a royal touch, yielding reproductive queens at much higher levels than other pairings.

The new finding could overturn the long-held belief that there is little genetic influence in ant caste systems.

"It's a genetic compatability effect," Tanja Schwander, biological researcher at Simon Fraser University in British Columbia and lead author of the paper. "The work shows that queens have to be compatible with a specific male to produce either workers or queens.

How social insect colonies function can give scientists insight into how social behavior evolved. Ant colony members generally have well-defined roles. Sterile workers take care of day-to-day tasks like finding food and rearing young while a queen mates and produces offspring. In the end, though, the workers' hard work is rewarded when the queen passes their very similar genes on to the next generation. E.O.

Wilson coined the term superorganism for exactly this type of cooperative group.

Biologists had long theorized that environmental factors drove the differentiation of similar ant eggs into the wildly different castes of queens and workers. But there wasn't much actual data on the subject.

"People just assume that this is environmental," Schwander said.

But if a specific mother-father genetic combination is required to create a queen, it argues strongly that genetics play a role in determining the social structure of the colony. Schwander's conclusion matches that of a separate group of researchers publishing in the smaller journal American Naturalist on a different type of ant.

"Caste determination in most social insects likely involves both nature and nurture," said Chris Smith, a biologist at the University of Illinois and lead author of that paper.

Schwander's data wasn't easy to come by, which could explain why previous assumptions about insect colonies have remained untested.

Heading out to the desert near Portal, Arizona, Schwander had to devise a system for capturing males and queens from different colonies in the

Arizona desert.

The species in the study, *Pogonomyrmex rugosus, *has the useful property of streaming out of its colonies in response to summer rainfall, which can be simulated with exactly eight gallons of water applied with the the watering can (above).

When the insects ran out of the colonies, the biologists collected them in tent-like nets and selectively coaxed ants from different colonies into crossbreeding. All told, the study took three summers and months of lab work raising the products of these matings to find the genetic compatibility effect.

"It's hardcore field work," Schwander said.

*Images:1. A close-up of Schwander's ant of choice: **Pogonomyrmex rugosus/Science. 2. Schwander's team's ant-catching field set-up/Schwander. *

Citation: "Genetic Compatibility Affects Queen and Worker Determination."

doi: 10.1126/science.1162590

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