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Fire Ant Queens Call the Shots in Battle of the Sexes

Researchers have long known that in social insect societies, queens wield tremendous power, laying eggs to the exclusion of the other females in the colony. Now new research reveals that some queens are even more tyrannical than previously thought. According to the results of a study published today in the journal Science, queen fire ants can even influence the ratio of males to females in the colony.

Conventional wisdom holds that the female workers who raise the young control the sex ratio, starving or destroying unwanted larvae. Owing to a quirk of ant reproductive biology, the female workers are three times more closely related to the queen's female offspring than they are to the males, so, in theory, the female workers should skew the sex ratio in favor of females. Generally, observations bear this out. But biologists have found a few puzzling exceptions to the rule, noting that some fire ant colonies contain many more males than predicted.

To find out who in the colony really controls the sex ratio, Laurent Keller of the University of Lausannne and his colleagues took queens from male-dominated colonies and female-dominated colonies and switched them. The results were striking. Within five weeks, the colonies reflected the sex ratios of the colonies from which the queens came. That is, queens from male-dominated colonies managed to convert female-dominated colonies into male-biased ones, and queens from female-dominated colonies transformed male-dominated colonies into female-biased ones.

The queens exert this influence by limiting the number of male or female eggs. But considering that she is equally related to all her offspring, exactly why a queen should show a preference at all remains a mystery.

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