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Origins of huge-headed 'supersoldier' ants

A supersoldier communicates with a minor worker from the hyper-diverse ant genus Pheidole.
[Photo courtesy of Alex Wild/alexanderwild.com]

Most ant species in the Pheidole genus have two social groups, or castes: workers and solders. Some also produce "supersoldiers." These large ants block their nest entrance with their extra-large heads and fight with invading ants during army ant raids.

Although there are 1,100 different species of Pheidole ants worldwide, just a few of them produce supersoldiers.

A new study shows that the genetic tools that ants need to produce supersoldiers evolved in a common ancestor of all Pheidole species. And, modern-day species still have the ability to produce these big-headed fighters, although just a handful of species have actually done so.

Rajendhran Rajakumar of McGill University in Montreal, Canada and colleagues were able to induce the development of supersoldiers one of these species, P. morrisi, by dabbing the larvae with a growth hormone. This finding suggests environmental cues can switch on the genetic machinery that produces supersoldiers.

The researchers suggest that hanging on to an ancestor's developmental "toolkit" can be an important way for organisms to evolve new physical traits. Their research appears in the 6 January 2012 issue of the journal Science.