Mushroom Growing Out Of An Ancient Ant's Butthole Is New Fungal Species

This tiny mushroom sprouted from an ant's rectum around 50 million years ago. Image credit: George Poinar Jr., OSU

Mycology is a fascinating branch of science, delving into the secret lives of fungi, whose beauty is often underrated and little celebrated. A mushroom found preserved in a 50-million-year-old piece of amber certainly demonstrates their beauty – that is, if you ignore the fact it’s growing out of an ant’s rectum.

While comical, with just a peppering of gross, the finding is a significant one. Published in the journal Fungal Biology, the specimen represents not only a new genus and species of fungus, but also the oldest known example of a fungus parasitizing an ant. That's a lot of academic value resting on the shoulders of a humble butt mushroom.

The unlucky ant is thought to have been a carpenter ant, found in Europe’s Baltic region infected with the newly named fungus Allocordyceps baltica. While mushrooms are what we most often see, they only constitute the reproductive body of a fungus with the rest often residing out of sight either in the substrate or the body of a host. The same is true of the A. baltica residing inside the ancient carpenter ant, as while the mushroom is emerging from the rectum, the vegetative part of the fungus is in its abdomen and neck.

"Ants are hosts to a number of intriguing parasites, some of which modify the insects' behavior to benefit the parasites' development and dispersion," said first author George Poinar, emeritus professor integrative biology at Oregon State University, in a statement. "Ants of the tribe Camponotini, commonly known as carpenter ants, seem especially susceptible to fungal pathogens of the genus Ophiocordyceps, including one species that compels infected ants to bite into various erect plant parts just before they die."

ant mushroom rectum
The new species and genus of mushroom can be seen poking out of the ant's butt. Image credit: George Poinar Jr., OSU

The involuntary behavior (earning Ophiocordyceps the nickname "zombie fungus") is a logical move on the part of the fungus, as it sends the ant on its merry way to a location that is ideal for a spot of spore dispersal. Its fruiting body, a cup-shaped structure called an ascoma, sends its spores drifting in the breeze from the high position, optimizing its chances of spreading and infecting other ants. The new fungal genus and species has this in common with Ophiocordyceps, with its fruiting body visible in the amber.

"We can see a large, orange, cup-shaped ascoma with developing perithecia – flask-shaped structures that let the spores out – emerging from the rectum of the ant," continued Poinar. "The vegetative part of the fungus is coming out of the abdomen and the base of the neck. We see freestanding fungal bodies also bearing what looks like perithecia, and in addition we see what looks like the sacs where spores develop. All of the stages, those attached to the ant and the freestanding ones, are of the same species."

Here the mushroom can be see in the lower left quadrant of the carpenter ant's silhouette. Image credit: George Poinar Jr., OSU

What separates this ancient fungus from the established ant-infecting genus Ophiocordyceps is its route of exit from the body. While Ophiocordyceps usually erupts from the neck or head of its host, A. baltica went for the butthole. A rogue move, perhaps, but a pivotal one as the specimen constitutes the oldest known example of a fungus parasitizing an ant, rectal-exit or no.

"There is no doubt that Allocordyceps represents a fungal infection of a Camponotus ant," said Poinar. "This is the first fossil record of a member of the Hypocreales order emerging from the body of an ant. And as the earliest fossil record of fungal parasitism of ants, it can be used in future studies as a reference point regarding the origin of the fungus-ant association."


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