100-million-year-old amber preserved oldest animal societies

Fighting ants, giant soldier termites, and foraging worker ants recently discovered in 100-million-year-old amber in Myanmar provide direct evidence for advanced social behaviour in ancient ants and termites, scientists say. 

This proves that advanced sociality in ants and termites was present tens of millions of years earlier than indicated by the previous fossil record, according to researchers. 

Advanced sociality, or eusociality, a hallmark of which is reproductive specialisation into worker and queen castes, is essentially a phenomenon of the group of invertebrates known as arthropods. Queens and reproductive males take the roles as the sole reproducers while the soldiers and workers defend and care for the colony. 

Eusociality occurs in a range of arthropods, from some shrimp, beetles, and aphids, to various wasps, though the phenomenon is nowhere more pronounced than in honey bees, ants, and termites. 

Among vertebrates, eusociality is found in just two species of African mole rats."Ecologically, advanced sociality is one of the most important adaptive features for animals," said Dave Grimaldi from the American Museum of Natural History. "All ants and termites are social, and they are ubiquitous across terrestrial landscapes, with thousands of described species and probably even more that we have not yet found," said Grimaldi. 

Eusociality is thought to have appeared first in termites in the Late Jurassic, about 150-160 million years ago. However, before the new work, the earliest termites ever found that could definitively be tied to a caste system were from the Miocene, a mere 20 to 17 million years ago. A similar story held true for ants, whose evolutionary history with eusociality was also thought to be long, but only weakly supported by the fossil record. 

"In the Cretaceous amber we examine, the ants and termites represent the earliest branches of each evolutionary tree, and the species are wildly different from what their modern relatives look like today," said Phillip Barden from Rutgers University in US. 

A number of pieces of amber recently  recovered from Myanmar gave researchers the answer - eusociality was going strong in both groups during the Cretaceous. 

In termites, researchers made this determination based on the diverse anatomy of the animals, indicating the presence of castes. They found six different termite species preserved in the amber, two of which are new to science. The amber ant fossils froze a number of eusocial behaviours in time. Those include - the presence of different castes, including queen ants and workers; groups of worker ants in single pieces of amber, probably nestmates foraging together; and two workers of different ant species engaging in combat.

The findings were published in the journal Current Biology.