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Humans aren’t the only ones capable of saving lives with amputation.
Florida carpenter ants have been observed nibbling on 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 an amputation make it through the process and continue their nest duties just fine, even after 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 research found that different species of ants called Matabele ants or Megaponera analis use their mouths to secrete antimicrobial compounds to clean wounds and prevent potential infections. The compounds are produced by what are known as the metapleural glands.
Most ants have these glands. However, over time some species – including Camponotus floridanus, also known as carpenter ants – have lost them through evolution.
Most species of ants without metapleural glands are arboreal, meaning they live in trees, said the study’s lead author Erik Frank, a behavioral ecologist at the University of Würzburg in Bavaria, Germany.
“We think their arboreal lifestyle may expose them to fewer pathogens than colonies living underground,” Frank said.
When the pandemic broke out, Frank and his colleagues planned to continue studying Matabele ants in Ivory Coast. As a result, the team moved to study the common carpenter ants available in his lab.
“I wanted to see how an ant species that couldn’t use antimicrobial compounds to treat wounds would care for its wounded,” Frank said.
The scientists were not prepared for what they observed: a type of surgery that had previously only been seen in humans.
Red-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 from competing ant colonies, which can result in injury.
Study co-author Dany Buffat, a graduate student at Switzerland’s University of Lausanne, first observed the ants cleaning and amputating wounds.
“The biggest surprise was definitely the fact that amputations are being done in the first place,” Frank said. “I never expected it, and when our (master’s student) Dany Buffat first described this behavior to me, I didn’t believe it. It wasn’t until he showed me the videos that I really appreciated what we had come across.”
Bart Zijlstra
One carpenter ant can be seen cleaning the wound of another ant.
As the team watched the ants in action, lead study author Dr. Laurent Keller, an evolutionary biologist at the University of Lausanne, noted another surprise: The ants performed the amputation only when the leg injury occurred on the thigh or femur. After biting the leg, the ants used their mouthparts to lick the wound and presumably remove the bacteria.
However, if the injury was on the lower leg or tibia, the ants would only lick the wound vigorously, resulting in a 75% survival rate.
To understand why the ants were so specific in their care and re-injury in a laboratory setting, the researchers removed a single ant from a nest, worked with small colonies of 200 ants, and used microscissors to make controlled cuts on the ant’s leg. .
“Beforehand, we would put the ants on ice for a few minutes to calm them down and make them easier to handle,” Frank said. “We carefully took one out of the nest, put it on ice and then cut off the leg. Once the ant wakes up again (after another few minutes), it will be released back into the colony to be with its nestmates.
In 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 take a closer look at the insect’s injuries
and how their bodies react. The amount of muscle on the ants’ thighs ensures that a
a blood-like fluid called hemolymph circulates. While ants do not have human counterparts
heart, have several heart pumps and muscles throughout the body that perform the same function.
A thigh injury impedes circulation, Frank said, and because blood flow is reduced, bacteria can’t circulate out of the wound and through the body as quickly, meaning amputation can prevent bacteria from spreading throughout the ant’s body.
Bart Zijlstra
An ant bites another’s leg after sustaining a thigh injury.
Meanwhile, the lower leg of ants does not contain any muscles needed for blood circulation. But any wound there would quickly introduce bacteria into the body and there would be no time for amputation.
“In the tibial injury, the flow of haemolymph was less impeded, meaning bacteria could enter the body more quickly. Whereas with a femur injury, the speed of blood circulation in the leg was slowed,” Frank said.
The researchers observed that the ant-assisted amputations took about 40 minutes, so the insects appeared to choose femur amputations but not tibia amputations.
“Because they are unable to cut off the leg quickly enough to prevent the spread of harmful bacteria, the ants try to reduce the chance of a fatal infection by spending more time cleaning the tibial wound,” Keller said.
Scientists are still trying to piece together the intricacies underlying this seemingly innate ant behavior.
“Workers must have learned through evolution that amputation was an effective way to prevent infection and that it increased colony productivity by increasing the number of workers who could participate in colony tasks,” Keller said.
These amputations are thought to be altruistic behaviors because the ants must expend time and energy to help others, Keller said.
“The fact that ants are able to diagnose a wound, determine whether it’s infected or sterile, and treat it accordingly over a long period of time with other individuals — the only medical system that can rival the human one,” 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 put their fingers to their lips after a paper cut.
“We just instinctively put our finger in our mouth and suck it, and we don’t actively think that we want to apply the antiseptic proteins in our saliva to the wound to prevent infection,” Frank said. “It’s probably similar in ants.” There was a strong enough evolutionary pressure for them to display two different behaviors to two different types of injury to maximize their (nest mates’) chances of survival. How they can tell them apart is another question and one I’m working on right now.”
Now scientists want to find more examples of wound care not only in ants, but throughout the animal kingdom.
“We will continue to study wound-care behaviors in other ant species and try to understand their evolutionary origins,” Frank said. “What was the behavior of the ancestors when treating wounds? Why do some amputate while others use antimicrobials?