Carpenter ants (Camponotus), a diverse genus of large ants indigenous to many forested parts of the world, can selectively treat the wounded limbs of fellow nestmates — either by wound cleaning or amputation.
Injured individual (marked in yellow) of Camponotus floridanus receives wound care by a nestmate. Image credit: Frank et al., doi: 10.1016/j.cub.2024.06.021.
Open wounds pose major infection and mortality risks in animals. To reduce these risks, many animal species apply antimicrobial compounds on their wounds.
In 2023, researchers discovered that a different ant species, Megaponera analis, uses a special gland to inoculate injuries with antimicrobial compounds meant to quell possible infections.
What makes Florida carpenter ants (Camponotus floridanus) and other species of the genus Camponotus stand out is that because they have no such gland, they appear to be using only mechanical means to treat their nestmates.
University of Würzburg’s Dr. Erik Frank amd his colleagues found that this mechanical care involves one of two routes.
The ants would either perform wound cleaning with just their mouthparts or perform a cleaning followed by the full amputation of the leg.
To select which route they take, the ants appear to assess the type of injury to make informed adjustments on how best to treat.
In the study, two types of leg injuries were analyzed, lacerations on the femur and those on the ankle-like tibia.
All femur injuries were accompanied by initial cleaning of the cut by a nestmate, followed by a nestmate chewing off the leg entirely. In contrast, tibia injuries only received the mouth cleaning.
In both cases, intervention resulted in ants with experimentally infected wounds having a much greater survival rate.
“Femur injuries, where they always amputated the leg, had a success rate around 90% or 95%. And for the tibia, where they did not amputate, it still achieved about the survival rate of 75%,” Dr. Frank said.
“This is in contrast to the less than 40% and 15% survival rate for unattended infected femur and tibia abrasions, respectively.”
The scientists hypothesized that the preferred path of wound care could be related to the risk of infection from the wound site.
Micro-CT scans of the femur showed it is largely composed of muscle tissue, suggesting it plays a functional role of pumping blood, referred to as hemolymph, from the leg into the main body.
With an injury to the femur, the muscles become compromised, reducing their ability to circulate potentially bacteria-laden blood.
The tibia, on the other hand, has little muscle tissue and thus little involvement in blood circulation.
“In tibia injuries, the flow of the hemolymph was less impeded, meaning bacteria could enter the body faster. While in femur injuries the speed of the blood circulation in the leg was slowed down,” Dr. Frank said.
“You may expect, then, if tibia damage results in faster infections, amputating the full leg would be most appropriate, but the opposite is observed.”
“It turns out the speed at which the ants can amputate a leg makes a difference.”
“An ant-assisted amputation takes at least 40 minutes to complete.”
“Experimental testing demonstrated that with tibia injuries, if the leg was not immediately removed post-infection, the ant would not survive.”
“Thus, because they are unable to cut the leg sufficiently quickly to prevent the spread of harmful bacteria, ants try to limit the probability of lethal infection by spending more time cleaning the tibia wound,” said Dr. Laurent Keller, a evolutionary biologist at the University of Lausanne.
“The fact that the ants are able to diagnose a wound, see if it’s infected or sterile, and treat it accordingly over long periods of time by other individuals — the only medical system that can rival that would be the human one.”
Considering the sophisticated nature of these behaviors, a reasonable next thought would be how these ants are capable of such precise care.
“It’s really all innate behavior. Ant behaviors change based on the age of an individual, but there is very little evidence of any learning,” Dr. Keller said.
The findings were publsihed in the journal Current Biology.
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Erik.T. Frank et al. Wound-dependent leg amputations to combat infections in an ant society. Current Biology, publihsed online July 2, 2024; doi: 10.1016/j.cub.2024.06.021
This article was adapted from an original release by Cell Press.
Source : Breaking Science News