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Humans are not the only ones capable of performing amputations to save lives.
Florida carpenter ants have been observed biting off injured limbs of nestmates, depending on the location of the wounds, to help their counterparts survive, according to a new study.
About 90% to 95% of ants that receive amputations make it through the process and continue with their tasks inside the nest just fine, despite losing a leg, the researchers found.
The study, published Tuesday in the journal Current Biology, builds on previous findings published in 2023 by the same international team of scientists.
This study found that a different species of ants called Matabele ants, or Megaponera analis, use their mouths to secrete antimicrobial compounds to clean injuries and prevent potential infections. The compounds are produced by what are known as metapleural glands.
Most ants have these glands. But over time, some species – including Camponotus floridanus, also known as carpenter ants – have lost them evolutionarily.
Most ant species that lack metapleural glands are arboreal, meaning they live in trees, said study lead author Erik Frank, a behavioral ecologist at the University of Würzburg in the German state of Bavaria.
“We think their arboreal lifestyle may expose them to fewer pathogens than colonies that live underground,” Frank said.
Frank and his colleagues had planned to continue studying Matabele ants in Ivory Coast when the pandemic hit. As a result, the team moved to study the common carpenter ants available in his laboratory.
“I wanted to see how an ant species that couldn’t use antimicrobial compounds to treat wounds would care for their injured,” Frank said.
The researchers were not prepared for what they observed: a type of surgical intervention that had previously only been seen in humans.
The reddish-brown Florida carpenter ants, which reach about 1.5 centimeters (about three-fifths of an inch) in length, can be found nesting in rotting wood throughout the southeastern United States. They must defend their nests against rival ant colonies, which can result in injury.
Study co-author Dany Buffat, a graduate student at the University of Lausanne in Switzerland, first observed the ants performing wound cleaning and amputation procedures.
“The biggest surprise was obviously the fact that they do amputations in the first place,” Frank said. “I never expected this, and actually when (our master’s student) Dany Buffat first described the behavior to me, I didn’t believe it. It wasn’t until he showed me the videos that I really appreciated what we were stuck with.”
As the team observed the ants in action, senior study author Dr. Laurent Keller, an evolutionary biologist at the University of Lausanne, noted another surprise: The ants performed an amputation only if leg injuries occurred in the thigh or femur. After biting the leg, the ants would use their mouthparts to lick the wound, cleaning and likely removing bacteria.
But if the injury was on the lower leg, or tibia, the ants would lick the wound intensely, resulting in a 75% survival rate.
To understand why the ants were so specific in their functions and to recreate the injuries in a laboratory setting, the researchers would remove a single ant from the nest, working with small colonies of 200 ants, and use microscissors to make controlled cuts on the ant’s leg. .
“Before, we would put the ant on ice for a few minutes so it would calm down and be easier to manipulate,” Frank said. “We would carefully take one out of the nest, put it on ice and then cut off the leg. Once the ant woke up again (after a few more minutes) it would be released back into the colony to be with its nestmates.
For ants with femur or tibia injuries that were not treated in isolation, less than 40% and 15% survived, respectively.
The team also performed CT scans of the ants to get a closer look at the insect injuries
and how their bodies react. A bunch of muscles inside the ant’s thighs ensure that a
Blood-like fluid, called hemolymph, circulates. While ants do not have like humans
hearts, they have several heart pumps and muscles throughout their body that perform the same function.
Injuries to the thigh cut off that circulation, Frank said, and because blood flow is reduced, bacteria can’t circulate from the wound and through the body as quickly, meaning an amputation can prevent bacteria from spreading throughout the body. the body of the ant.
Meanwhile, the lower leg of ants does not contain any muscles necessary for blood circulation. But any wound there would quickly introduce bacteria into the body and there would be no time for an amputation.
“In the tibial injuries, the flow of haemolymph was less obstructed, meaning bacteria could enter the body more quickly. While in femur injuries, the speed of blood circulation in the leg slowed down,” said Frank.
The researchers observed that the amputations assisted by the ants took about 40 minutes to complete, which is why the insects appeared to choose the femur amputation but not the tibia amputation.
“So, because they are unable to cut the leg fast enough to prevent the spread of harmful bacteria, the ants try to limit the probability of fatal infection by spending more time cleaning the tibial wound,” Keller said.
Researchers are still trying to piece together the complexities underlying this seemingly innate behavior of ants.
“Workers must have learned over evolutionary time that amputation was an efficient way to prevent infection and that it increased colony productivity by increasing the number of workers who could contribute to colony tasks,” Keller said.
These amputations are considered altruistic behavior because ants must spend time and energy helping others, Keller said.
“The fact that ants are able to diagnose a wound, see if it’s infected or sterile, and treat it consistently over long periods of time from other individuals — the only medical system that could rival that would be that human,” Frank said. .
But Frank said he doesn’t think ants consciously know what to do. Instead, it may be more instinctive, similar to how people bring their fingers to their lips after a paper cut.
“We’ll just instinctively put our finger in our mouth and suck it and not actively think that we want to apply the antiseptic proteins in our saliva to the wound to prevent an infection,” Frank said. “This is likely to be similar for ants. There was quite a strong evolutionary pressure for them to display two different behaviors to two different types of wounds to maximize the chances of survival for it (the nestmates). How can tell them apart is another question and one I’m currently working on.”
Now, researchers want to find more examples of wound care, not just in ants, but across the animal kingdom.
“We will continue to study wound care behavior in other ant species and try to understand its evolutionary origins,” Frank said. “What did ancestral wound care behavior look like? Why do some amputate while others use antimicrobials?”
