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article imageSecrets of the 'zombie' ant fungus

By Tim Sandle     Aug 23, 2014 in Science
The parasitic fungus that kills its ant hosts outside their nest in order to reproduce and transmit the infection, manipulates its victims to die in the vicinity of the colony, ensuring a constant supply of potential new hosts.
This is the main finding from some new research into Ophiocordyceps camponoti-rufipedis (otherwise known as 'the zombie ant fungus'). Previous studies have shown that the fungus controls the behavior of carpenter ant workers of the ant species Camponotus rufipes. The fungus also seems to be able to program the ants to die with precision, attached to leaves in the understory of tropical forests.
After climbing vegetation and biting the veins or margins on the underside of leaves, infected ants die, remaining attached to the leaf, where they serve as a platform for more fungal growth. The fungus grows a stalk (or stroma,)which protrudes from the ant's body. Spores later develop in the and are discharged onto the forest floor below, where they can infect a new wave of foraging ants from the colony.
This fungal reproductive activity has developed to take place outside of the ant colony. Scientists reason that this is because of the ants' social immunity, where is collective action taken to limit disease spread.
In the new study, biologists tested this social immunity phenomenon by placing 28 ants freshly killed by the fungus inside two nests — 14 in a nest with live ants and 14 in one with no ants. The researchers found that the fungus was not able to develop properly in any of the 28 dead bodies. Interestingly, in the nest with live ants, nine of the 14 infected cadavers disappeared, presumably removed by the ants in an effort to thwart the disease organism.
To look further at how the fungus operates, the researchers set out to record the prevalence of the fungus among ant colonies within the vicinity of the Mata do Paraíso research station in southeast Brazil. After marking and searching 22 transects covering a total of 16,988 square miles, the scientists discovered that all 17 nests found had ant cadavers attached to leaves beside the colony. By measuring the position of manipulated ants and plotting these locations with respect to the nest, the researchers established that infected ants die on the "doorstep" of the colony.
The research, carried out via Penn State University, have been published in the journal PLOS One. The paper is titled "Long-Term Disease Dynamics for a Specialized Parasite of Ant Societies: A Field Study."
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