An accidental yet lucky shot led to a new discovery about the symbiosis between an “ant-plant” tree and the ants who live in them.
Perhaps the humans are still too slow to repair their only habitat, but a few ants in Panama are not. At least, that’s what a 15-year-old with a slingshot found out when he accidentally hit a Cecropia tree with a clay ball.
Alex Wcislo, a student at the International School of Panama, fired the shot one day during the early days of the COVID-19 pandemic. He said he was bored and had nothing much to do.
What he noticed, though, was that the clay ball pierced clear through a branch of the tree, which is known to be an “ant-plant” tree. The trees have a symbiotic relationship with the Azteca alfari ants that live in them, and the ants are known to protect their trees from herbivore challengers.
When Alex came back the next day, the ants had already patched up the hole in the tree. So he and four of his high-school friends wanted to know more, and the next thing they knew, their names were included in the list of authors whose research on the discovery was just published in the Journal of Hymenoptera Research.
The teens paired up with scientists at the Smithsonian Tropical Research Institute (STRI) who had studied the ant behavior before. Now, they wanted to investigate this new development.
As with other known symbiotic relationships in the natural world, the ants were unlikely to care much about a tree wound unless it presented a threat to their colony and brood. In fact, the scientists weren’t sure they’d care at all, because such a wound poses no direct threat to their food supply—the basic currency of their transactions with the trees.
But they found that the Azteca ants did get to work when the tree was wounded. They started patching holes drilled into 22 trees that were known homes for the ants across the Cárdenas community and in the nearby Bosque Urbano de Cárdenas forest. The holes were intentionally created to replicate the initial 9-millimeter slingshot hit.
The young scientists then collected the data from June through November 2020, during the tropical forest rainy season. On average, the ants began their repair work in about 2.5 hours and usually had the tree wound closed within 24 hours. If the wound site was near an ant brood, the repair was faster and completed in about five hours.
The ants appeared to use fiber from the tree itself, likely using tree sap to bind the fibers together and seal the wound. The STRI researchers couldn’t find evidence of any secretions that came from the ants themselves, which would suggest an even stronger symbiosis with the tree. Neither could they rule it out, though.
“Ants carried small pieces of plant material and patched the hole from inside and outside the nest; in the latter case, ants exited from an adjacent internode with building materials,” the study authors said. “Ants applied their pulp to the hole working inwards around the entire circle.”
But how would the ants know to respond to a slingshot injury? The short answer is that they don’t, but likely have evolved to repair tree wounds caused by Bradypus sloths with sharp toenails that live in the same trees.
There were some differences in behavior that warrant further study. Not all of the ant colonies did the repair work when wounds were placed in their trees. The scientists think it may be because a hole presented no direct threat to their own brood, or that it may have to do with the age of the tree and the size of the colony.
They also noted that extensive damage was not repaired, perhaps as if the ants’ sense of “tree triage” meant there was no point in expending the energy and resources.
As for the new lesson in biodiversity and habitat?
“Sometimes messing around with a slingshot has a good outcome,” says Alex. “This project allowed us to experience first-hand all the intricacies behind a scientific study.”