Accidental tree wound reveals novel symbiotic behavior

Despite significant movement restrictions during the first wave of the pandemic in Panama City, a group of curious high school students roamed their neighborhood drilling holes into Cecropia trees and documenting how Azteca alfari ants responded to damage to their host plant.

During the pandemic, five curious high school students accidentally discovered how Azteca alfari ants respond to damage to their Cecropia host trees. Photo by Donna Conlon

One afternoon, during the early days of the COVID-19 pandemic in Panama, a bored teenager with a slingshot and a clay ball accidentally shot entry and exit holes in a Cecropia tree trunk. These are “ant-plant” trees, which famously cooperate with fierce Azteca ants; the trees provide shelter and food to the ants, and in exchange the ants defend their leaves against herbivores. The next morning, to his surprise, the Azteca alfari ants living within the Cecropia trunk had patched up the wound.

This unexpected occurrence drove five curious high school students, with time on their hands, to participate in the Smithsonian Tropical Research Institute’s (STRI) volunteer program, and they enlisted STRI scientist William T. Wcislo’s help in devising their experiment. Despite significant movement restrictions during the first wave of the pandemic, they roamed their neighborhood drilling holes into Cecropia trees and documenting the ants’ responses to the damage.

They found that as soon as the plants had holes drilled into them, the ants ran to the wound area and began patching it up. Within 2.5 hours, the size of the hole had been significantly reduced and it was often completely repaired within 24 hours.

Although some Azteca ants are known to defend their Cecropia host plants against herbivores, these new results, published in the Journal of Hymenoptera Research, reveal that not only do the ants behave in ways to minimize damage to their hosts, but when damage does occur, they actively work to fix it, particularly when their brood is directly threatened.

“I was totally surprised by the results,” says William Wcislo. “And I was impressed by how they developed a simple way to test the idea that ants repair damage to their home.” 

Azteca ant and Cecropia plant responses to wounds in the stems a a sealed hole after 24 hours, but not yet filled in to the stem surface (arrow) b a fully patched and filled-in hole after 24 hrs, oozing sap from the ant-sealed wound (arrow) c a natural plant scar surrounding a 6.4 mm hole that was fully sealed by the ants, approximately 5 months later d a hole in a plant without ants after 24 hrs, showing the green wall of the opposite side of the stem (arrow).

Sloths and silky anteaters often visit Cecropia trees and their sharp toenails sometimes pierce the wood, so the researchers speculate that these occurrences, which are far more common and ancient threats to the Cecropia than teenagers shooting clay balls at them, could have led Azteca alfari ants to evolve the observed repair behavior when their host plant is damaged. 

Their experiment also left them with new questions, since not all of the ant colonies repaired the damage to their host plants. Understanding what factors influence the ants to take action could be the subject of future research for these budding scientists, although perhaps to be addressed after graduating from high school.

“Sometimes messing around with a slingshot has a good outcome,” said lead author Alex Wcislo. “This project allowed us to experience first-hand all the intricacies behind a scientific study. All in all, it was a great learning experience, especially considering the difficulties associated with fulfilling this due to COVID-19.”

Research article:

Wcislo A, Graham X, Stevens S, Toppe JE, Wcislo L, Wcislo WT (2021) Azteca ants repair damage to their Cecropia host plants. Journal of Hymenoptera Research 88: 61-70. https://doi.org/10.3897/jhr.88.75855

Beetle named after actress & biologist Isabella Rossellini for her series about animals

A new species of beetle with remarkably long genitalia that hint at a curious evolutionary “sexual arms race” has been described from Malaysian Borneo.

The new insect was named after actress and biologist Isabella Rossellini in honour of her stage shows and Webby Award-winning series of films about animal reproduction, featured on SundanceTV.

The species is described by scientists Menno Schilthuizen and Iva Njunjic of Naturalis Biodiversity Center and Universiti Malaysia Sabah, and Michel Perreau, Sorbonne Université, Paris. Their paper is published in the open access journal ZooKeys.

The new species, Ptomaphaginus isabellarossellini, finds a place among the 30 known species of round fungus beetles (subfamily Cholevinae) recorded by the authors from the island of Borneo. Of these, there are a total of 14 which had remained unknown to science until now.

The reason why the scientists named this particular species after the famous actress is its genitalia. The beetle’s penis carries a long, whip-like thread, called flagellum, whereas the female has a similarly long tube leading up to a sperm storage organ.

Lead author Menno Schilthuizen, who himself has previously released a simultaneously educative and entertaining book about the evolution of genitals, says that such exaggerated male and female genitalia often betray an “evolutionary sexual arms race”.

On the male side, natural selection favours longer genitalia because of the ability to directly reach the female’s sperm storage organ. However, female beetles would rather retain their right to favour the DNA of a certain mate over the rest. The upshot is that, over long periods of evolution, penises get longer and vaginas get deeper. Similar evolutionary genital exaggeration is also known in rove beetles and ducks.

“This is better than winning the Oscar,” says honoured Isabella Rossellini.

The Italian-born actress, filmmaker, author, philanthropist, and model has even featured the new beetle in her new Link Link Circus stage shows. Dealing with animal behaviour, the series will be touring theaters in Europe this fall.

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Original source:

Schilthuizen M, Perreau M, Njunjic I (2018) A review of the Cholevinae from the island of Borneo (Coleoptera, Leiodidae). ZooKeys 777: 57-108. https://doi.org/10.3897/zookeys.777.23212