March 6 (UPI) -- Turtle ants have adopted a largely defensive posture and abandoned the offensive tendencies of their relatives. New research suggests the strategic shift was made possible by their partnership with 46 million year-old gut bacteria.
More than a decade ago, Drexel University scientists realized ant species with nutrient-poor diets also hosted unique bacterial symbionts. To better understand these relationships, researchers decided to take a closer look at turtle ants, a group of species belonging to the neotropical genus Cephalotes.
In the lab, scientists fed the ants urea, the main waste ingredient in urine. They also fed them antibiotics to kill the bacteria living in ants' digestive system. Without the help of their bacterial symbionts, the ants were unable to consume sufficient levels of nitrogen.
Animal waste, including urine and feces, is rich in nitrogen, but the nutrient is inaccessible to most animals without the help of microbes.
With the help of their microbial partners, turtle ants can subsist on poor diets. As a result, they no longer compete with other ants for high-quality meals. They've abandoned the strong lower mandible that allows other ants to rip apart larger invertebrates. They've also lost their ability to sting.
In the place of offense, turtle ants have invested in defense, evolving thicker armor and a "specialized caste of adults that use their heads to plug the entrances of their hollow tree branch nests," according to Drexel researcher Jacob Russell.
"That armor may be possible due to the large contributions gut microbes make to their nitrogen budgets," Russell said in a news release.
The ants are very protective of their gut microbes. They use anal secretions to share their microbes with one another and have evolved a fine-mesh filter in the digestive tract to serve as a protective barrier.
"This has likely helped to reinforce the integrity of these ancient bacterial communities," Russell said.
Russel and his colleagues detailed their study of turtle ants in the journal Nature Communications.
"This work illustrates that members of complex communities can evolve together, laying the groundwork for future research on how these organisms evolve in response to reliable partnerships," Russell said.