The fungus Ophiocordyceps unilateralis is probably one of the most famous parasites in the world, and no wonder, since it is capable of altering the behavior of ants to complete their life cycle in a rather terrifying way.
Its unfortunate hosts are a type of carpenter ants, Camponotus leonardi , which live in a kind of nests built high in trees in tropical areas. As the biochemist and popularizer David G. Jara explains in his book The Grasshopper Enchanter and other essays on the natural history of parasites , the spores of this peculiar intruder initially attack the external cuticle of the insect to develop the fungus inside. After a few days, ” the ant is subjected to the absolute control of the fungus, showing an abnormal behavior , very different from that of its non-infected companions.” In this way, the insect loses its will and control of its actions, beginning to make uncontrolled and random movements until it falls from its nests to the leaves located at ground level . When the ant finally dies, the fungus develops a fruiting body in the form of a stem that “germinates inside the ant, goes through the head of the insect and begins to grow towards the sky.” This allows it to release its spores in a cool and humid place, protected from radiation from above. The spores will wait for some other unfortunate ant to leave the heights (something that can happen, for example, under conditions of food scarcity) to infect it and start the cycle again.
How does the fungus manipulate the behavior of the carpenter ant? The answer is found in the extended phenotype, a concept coined by biologist Richard Dawkins in his famous book The Selfish Gene and which explains the suicidal behavior of some organisms when a parasite lodges inside them . Basically, the fungus is expressing its genotype (genes) in the ant’s phenotype (observable traits) and not in its own. Or, put another way, the ant’s behavior is not a consequence of the expression of its own genes but of those of the parasite.
The terrifying relationship of parasitism between this type of fungus and its victims is quite well studied and more and more details about its operation are known. For example, in 2012 the magazine PLOS ONE echoed the discovery of an unusual defensive strategy against the zombie fungus: another fungus. ” It is a case in which biology is more than fiction, ” explained the researcher at Pennsylvania State University and author of the article David Hughes. “The hyperparasitic fungus castrates the fungus that turns the ant into a zombie to prevent it from expelling its spores. Thanks to the fact that the hyperparasitic fungus prevents the spread of these spores, fewer infections will occur in other ants ”.
An ancient species that was introduced through the rectum of ants
As if that were not enough, and to continue challenging the imagination, a few weeks ago the magazine Fungal Biology revealed the discovery of a new species of fungus similar to those of the genus Ophiocordyceps that invaded ants by entering their rectum. It is the oldest known specimen of a fungus that parasitizes ants so far: it was found in a piece of amber about 50 million years old. This sample contained a carpenter ant of the genus Camponotus from whose rectal orifice the fungus emerged, which has been baptized as Baltic Allocordyceps .
It is a new genus and species of fungus that shares some characteristics with Ophiocordyceps , but also shows several unique developmental features, among them that the ascoma or sexual reproduction structure of the fungus does not arise from the neck or head of the ant. “In the sample you can see a large orange cup-shaped ascoma with perithecia – flask-shaped structures that let out spores – in development that emerges from the rectum of the ant,” explained George Poinar, a researcher at the State University of Oregon and first author of the article. “Separate fungal bodies are also preserved that have perithecia and what look like sacs in which the spores develop. All the phases, both those attached to the body of the ant and the independent ones, are of the same species.
For the authors, as it is the oldest known fossil record of fungal parasitism in ants, this finding will be useful to be used as a reference in future studies on the origin of the fungus-ant association and in which, surely, biology shows us will continue to surprise with discoveries that surpass the most convoluted stories of fiction.