In days of old were more ants bold? Among the 1100 species in the Pheidole ant genus today, most produce two castes: foragers and soldiers. But on very rare occasions, a small number of species generate so-called supersoldiers, ants with especially giant heads who bravely keep other ant species from invading their nests by blocking the entrances with their noggins and employing enhanced battle skills. Curious as to how these warriors develop, researchers examined the genomes of two Pheidole species that sometimes produce supersoldiers and identified the genetic machinery responsible for making this caste. When the researchers treated the larvae of these species with a growth hormone called methoprene, the larvae developed into supersoldiers. Then the researchers dabbed methoprene on the larvae of Pheidole species that don't usually make supersoldiers. The larvae developed huge heads and useless wings similar to those of supersoldiers, suggesting that environmental cues drive supersoldier development. Since all the ants in the genus seem to retain an ability to become supersoldiers, the militaristic adaptation must have evolved in a common ancestor but been repressed later by most species in the absence of these cues, the researchers report in Science today.
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