In a Brazilian rainforest, a pathogenic fungus infects an unsuspecting carpenter ant. The fungus takes over the insect’s mind, manipulating its behavior and causing it to abandon its colony and to wander around aimlessly. The ant, now a helpless “zombie,” is chemically compelled to bite and cling onto the surface of a leaf; the bite is carried out with such an anomalous force that it creates a telltale dumbbell-shaped scar on the leaf. The ant then dies, and the fungus takes over the cadaver. Finally, on the ant’s head, a single fungal stroma stalk grows, ready to fire more of the deadly spores towards the forest floor onto other passing ants.
Yes, it’s the stuff of nightmares—at least for the hapless little insects. The fungus, probably the insect world’s answer to the fictional Rage Virus, was originally thought to belong to a single species called Ophiocordyceps unilateralis. Now, scientists have discovered that the fungus is actually four different species—all of which can “zombify” ants, specifically those belonging to the tribe Camponotini (subfamily Formicinae). The four new fungi species named by the researchers are as follows: Ophiocordyceps camponoti-balzani, Ophiocordyceps camponoti-rufipedis, Ophiocordyceps camponoti-melanotici and Ophiocordyceps camponoti-novogranadensis. All of them were discovered in Brazil’s Atlantic rainforest system in the south-eastern region of the Minas Gerais state.
The study, published online last March in PLoS ONE, is significant because it reveals the hidden diversity of the zombie ant fungi. In addition, it also highlights the importance of studying the remarkably complicated biological interactions occurring in the world’s most threatened ecosystems. The Atlantic forest of Brazil is one of the most endangered biodiversity hotspots in the world. It is home to 20,000 plant species (40 percent of which are endemic) and yet less than 10 percent of the original forest remains today. This is bad news for scientists who are fighting time and tide to discover more new species.
Study leader Dr. David Hughes, an entomologist from the Pennsylvania State University, said in an interview with National Geographic: “it is tempting to speculate that each of the fungus has its own ant species that is best adapted to attack. This potentially means thousands of zombie fungi in tropical forests across the globe await discovery.”
Scaring ants since 48 million years ago
In 2010, Hughes and his partners, Conrad Labandeira from the Smithsonian Institution in the United States and Torsten Wappler from the Steinmann Institute in Germany, studied a 48-million-year-old leaf specimen from the Messel Pit, located near Frankfurt, Germany. On the specimen, they discovered distinctive markings that are similar to the scars being left behind by today’s ants after they go into a “death grip”—the powerful, chemically induced bite on the leaf surface which is the last phase of the parasitic fungus’s diabolical scheme. The discovery prompted the scientists to hypothesize that the fungus’s parasitic relationship with ants is relatively ancient and not a recent development.
Death grip bites often occur en masse. Previously, in a forest in Thailand, Hughes and his colleagues discovered high-density aggregations of ants that have died from Ophiocordyceps infection—an average of 26 dead ants per square meter. The macabre phenomenon led the scientists to call the aggregations “graveyards.”
All these discoveries are beginning to sound like a good plot for next summer’s zombie-thriller-cum-creature-feature B-movie, don’t you think?
Photo credit: David Hughes via PLoS ONE