“The level of sophistication they have evolved to care for their wounded is unmatched in the animal kingdom. Our human medical system would be the closest to that,” Erik Frank, a behavioral ecologist at the University of Würzburg who led the study, said in an interview Wednesday. “These amputations stopped infections from spreading into the body … in the same way that medieval amputations worked in humans,” he said, adding that the findings represent the first recorded example of a non-human animal performing an amputation on another member of its own species to save its own life. life.
A study published Tuesday in the journal Current Biology suggests that Florida carpenter ants (Camponotus floridanus) are able to distinguish between types of wounds and adjust their healing responses accordingly. It contributes to our growing understanding of ants’ sophisticated self-care strategies when injured, including sorting out the wounded and treating the infected with microbial agents.
The researchers observed amputations in the laboratory as performed by Florida carpenter ants, reddish, black, or brown ants that typically measure less than 1/2 inch in length. Unlike some other ants, Florida carpenter ants do not have the ability to produce antimicrobial secretions from their glands to fight pathogens in wounds. “We wanted to see how a species that had lost this gland would still care for its wounded,” Frank said.
The researchers decided to deliberately injure about 100 ants on the leg: either the femur (closer to the body) or the tibia (further down the leg) to compare how the ants in their colony responded. They found that the ants effectively performed amputations when their siblings sustained femur injuries, but never performed amputations when they sustained equivalent tibial injuries.
In the first case, in more than three-quarters of the cases, the entire leg of the injured insect was amputated by the auxiliary nesting partner.
Amputation of the ant took about 40 minutes and followed the same pattern each time: “They start licking the wound with their mouths and then move their mouths down the leg until they reach the shoulder. There they start biting quite ferociously for many minutes at a time,” Frank said. “An injured ant will sit still, let the procedure take place, and not complain until the leg is cut off.”
Among ants with femur injuries, 95 percent of those who received an amputation survived, while only 45 percent of those who did not receive an amputation survived, Frank said.
“Ants—in their world, in their context—have found a strategy that is highly effective and has a very, very high level of success,” Frank concluded.
Laurent Keller, an evolutionary biologist who also worked on the study, said the amputations were performed very efficiently. “It means that when they do the amputation, they have to do it in a very clean way to prevent bacteria from getting into the wound,” he said.
Unlike the treatment received by ants that sustained femur injuries, ants that sustained tibial injuries (further down the leg) were never observed being amputated from other nestmates. “In this case, they’re just cleaning the wound,” said Keller, who said the nestmates instead provided extended wound care that included lots of licking.
The wound cleaning method has also proven itself. While about 70-75 percent of those who received ant wound cleaning survived, only 15 percent of ants with tibial injuries survived when they were isolated from their ants and left unattended, Frank said.
One of the possible explanations that scientists offer for the decision when to perform an amputation related to how hemolymph—the fluid equivalent of blood—flows in invertebrates.
The theory has yet to be tested, but scans show that the tibial area of the leg has greater hemolymph flow than the femoral area, meaning that pathogens that get through the tibia will spread more quickly to the rest of the body. This in turn greatly shortens the opportunity for amputation to prevent the spread of infection. “If the wound is at the level of the tibia, then they don’t do the amputation.” This is because normally the blood – or hemolymph for insects – circulates quite quickly. So within 40 minutes, the blood has already carried the bacteria into the ant’s body,” explained Keller.
The ants’ painstaking efforts to tend to others’ wounds illustrate how social insects benefit from behaving altruistically, Keller said. “By helping each other, they are indirectly helping themselves,” he said.
“Evolutionarily speaking, colonies save a huge amount of energy by making sure their injuries are well preserved, rather than just throwing them out and replacing them with a new worker,” he said. Previous studies show that ants that have lost one or even two legs can still be productive members of their colony and return to their normal speed within a day – and are often deployed to carry out the most dangerous tasks. Added by: “Even in ant societies, the individual has value.”