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Division of labor in ants emerged over 100 million years ago

Ants live in large groups organized according to a highly specific division of tasks – a phenomenon called by biologists “eusociality.” There are three “casts,” each having a different role: the queen lays eggs, the males fertilize them, and the workers look after the offspring, forage for food, and build nests.

The complexity of ants’ social organization can be seen not only in their behavior, but also in their morphology. For instance, winged females take on the role of the queen, while wingless, infertile ones perform the tasks of the workers. But when exactly in their evolutionary history did this unique form of teamwork emerge?

By examining four fossils enclosed in amber (three adult female wingless ants and one incompletely developed pupa), a new study led by the University of Jena in Germany has found that this cooperative way of life most probably emerged in the early Cretaceous period (145 to 100.5 million years ago). 

“With the help of micro-computed tomography images, we were able to determine that the soft tissues of the insects have been exceptionally well-preserved,” explained study lead author Dr. Brendon E. Boudinot, an expert in Entomology and Phylogenetics at the University of Jena. “This enabled us to examine the precise structure of the brain and the transverse muscle fibers, for example, and thus compare the four specimens with each other in fine detail.”

The researchers established that two of the adult insects belonged to a previously unknown species of the extinct ant genus Gerontoformica, while the third ant and the pupa were both of the same species, Gerontoformica gracilis.

“As ant pupae are not mobile, it can be inferred that the adult insect carried it,” said Dr. Boudinot. “This brood transport, as it’s called, is a unique feature of ant coexistence based on their division of labor. The fossil therefore provides the first material evidence of cooperative behavior from the Cretaceous period: these ants looked after their young together, went in search of food together, and had different queen and worker castes.”

Thus, these fossil representatives are an important “missing link” between today’s ants and their ancient relatives, confirming that the highly complex and specialized social system of ants evolved sometimes in the Early Cretaceous, during the time of the dinosaurs.

The study is published in the Zoological Journal of the Linnean Society.   

By Andrei Ionescu, Staff Writer

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