Size of Ants' Thorax Evolves Based on Job in Colony

Tiny worker ants capable of carrying loads several times larger than their own body mass have uniquely evolved thorax segments that enable them to do their jobs, and queen ants' thoracic segments vary in shape depending on how they begin new colonies, according to scientists.

Writing in the open-access journal eLife, the researchers report ants grow the size of their thoracic segments based on the jobs they will perform as adults, which they say explains how worker ants are capable of hunting down prey many times their own size and carrying the kill back to the nest.

According to Roberto A. Keller, a researcher in the lab of Patrícia Beldade at the Gulbenkian Institute of Science in Portugal (IGC), the thoracic section closer to the head of worker ants is greatly enlarged and filled with strong neck muscles which power the head. A strong yet flexible neck, Keller suggests, is key to the ants' superstrength.

Queen ants, on the other hand, do not have such powerful neck muscles, and therefore have much smaller thoracic segments near their heads, Keller observed.

But the queen ant's thorax segments are uniquely evolved in their own way. A queen that leaves the nest to start a new colony - typically without the help of workers - will fly away and lay eggs in a new location to begin a new colony. In order to have enough energy to feed the colony and ensure the nourishment of the first generation, the queen will essentially dissolve her wing muscles and reabsorb them into her body. Keller and his colleagues observed queens having undergone this transformation to have have an enlarged thoracic wing segment, and an extremely reduced thoracic neck segment.

Queen ants from other species will begin a new colony by going through their own worker-like phase to hunt for and feed the new colony until there are enough workers to take on the role. Queen ants that do this have intermediate wing and neck segments of their thorax, the scientists reported.

"Our analysis of morphology shows that worker ants are much more than just smaller and wingless versions of queens, and have a body plan that provides great strength and maneuverability to their heads. It also shows that queens that start new colonies without the help of workers can have two types of body plans associated to whether they go through a worker-like hunting phase or not," Beldade said.

Keller added: "Our new findings might help explain the ants' extraordinary ecological success and evolutionary diversification in comparison to other social insects."