Many species use antimicrobial secretions from certain glands in an attempt to combat pathogens. However, some species, such as the Florida Carpenter Ant (Camponotus floridanus), have lost this gland over evolutionary time, and they now must find other ways to combat the problems that open wounds can cause to a colony. We now have evidence that the Florida Carpenter Ant is the first non-human animal to use amputations to treat infected individuals and can adapt the type of treatment depending on the wound location. 

 

 

Enter, amputations. Or, ant-putations.  

The researchers noticed that in response to workers with injuries to their legs, nestmates would often perform amputations. Further experiments revealed that the decision to amputate the leg was dependent on where the injury occurred on the leg. For example, 76% of individuals who had an injury to the femur experienced amputation by nestmates, but those that were injured on their tibia never experienced amputations by their nestmates, but did receive longer wound care. 

On average, amputations occurred around the four-hour mark post-injury and generally followed the same behavioral pattern for the amputation. The nestmate would begin to lick the wound, and then would move up the leg to the trochanter, which is the connection point between the femur and the coxa, which connects to the thorax. The nestmate would then use their mandibles to bite repeatedly until the leg was cut off.  

The researchers also assessed the survival rates and bacterial loads of ants that had experienced either a femur injury or a tibial injury, and then were exposed to a pathogen. The researchers either left the ant by itself, induced the amputation by their own hands, or returned the ant to the nest. Infected individuals with femur injuries that were isolated without an amputation had a lower survival rate and a higher bacterial load compared to the other treatments. Interestingly, infected individuals with femur injuries that received manual amputations at the trochanter one-hour post-infection from the researchers had similar survival rates and bacterial loads as those that were returned to the nest. This means that the amputations can be the make it or break it factor that allows the ants to survive. In addition, this also means that they are also potentially bringing back less pathogens into the nest.  

However, ants with tibial injuries were a completely different story. Infected individuals with tibial injuries who received amputations from the researchers at the trochanter one-hour post-infection had the same survival rates and bacterial loads as those that were infected and isolated. This means that amputation is not an effective tool for tibial injuries, which is what the researchers observed from the ants to begin with. However, ants that experienced tibial injuries, but were allowed to return to the nest had similar survival to the control ants, but featured an in-between bacterial load to the control ants and those that were infected but isolated. This indicates that nestmates are extremely important in management of potential disease entering the colony.  

The researchers additionally physiologically examined these ants to determine why amputations were so effective for femur injuries, but not tibial injuries. Using micro-CT scans, they examined the structure of the trochanter, femur, and tibia, and determined that the femur features a larger amount of muscle tissue. The destruction of muscles in the femur could potentially lead to less effective hemolymph circulation, which gives the ants more time to make their cuts, as it may be. The researchers additionally examined effectiveness of amputations in tibia injuries, and only those that were made immediately after pathogen exposure proved to be beneficial for those injured ants.  

This study emphasizes just how adaptable ants are as a species. With a couple of snips of their mandibles, they’re able to keep their fellow nestmates on the move and relatively healthy. With this kind of resourcefulness when it comes to injuries, it does bring to mind how resourceful they can be when faced with our tools and tricks of the trade when it comes to managing them.  

Article by: Laura Rosenwald, BCE

References

Frank ET, Buffat D, Liberti J, Aibekova L, Economo EP, Keller L. Wound-dependent leg amputations to combat infections in an ant society. Curr Biol. 2024 Jul 22;34(14):3273-3278.e3. doi: 10.1016/j.cub.2024.06.021. Epub 2024 Jul 2. PMID: 38959879.

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