According to the authors, the four varieties belong to the fungal pathogen species complex known as Ophiocordyceps unilateralis
. Each variety specifically attack different species of carpenter ants of the tribe Camponotini
. The Ophiocordyceps
fungus has a pan-global distribution in tropical forests. Several species of this type of fungus parasitize carpenter ants particularly in Africa, Australia, Brazil and Thailand.
The fungi attach themselves to the carpenter ants while they walk across the forest floor. The spores use enzymes to get inside the ant's body where the fungus begins to grow. About a week after being exposed to spores the ant enters a zombie-like state. The alteration of the ant’s behaviour consists in directing the ant to climb to a higher position in the forest canopy. Once the ant has reached a particular level in the vegetation it clings or fixes itself to a twig or the vein of a leaf where it dies. The fungus then grows out of the ant’s head and releases spores which can spread widely and have a better chance of infecting other ants. The environmental conditions, including height from the ground, prevalent temperature, humidity and orientation of the leaves where the ant stops its climb and dies, has been identified as specific to the best conditions required for the fungus to develop and produce the spores.
The study was carried out by scientists from Minas Gerais, Brazil, Surrey, United Kingdom and Pennsylvania, Unites States. It was published on-line March 2 in PLoS ONE
. The main relevance of the discovery reported by David P. Hughes (Penn State University) and colleagues resides in the identification, description and naming of four distinct species which were originally thought to be a single species
of the fungus. Each of the four species can "mind control" and kill a different host species of ant.
“This so-called zombie or brain-manipulating fungus alters the behaviour of the ant host, causing it to die in an exposed position, typically clinging onto and biting the adaxial surface of shrub leaves,”
write the authors in their report.
These types of mind-controlling fungus are known capable of destroying entire ant colonies
. As a response, the ants have evolved the ability to detect members of the colony which have been infected; healthy ants will carry the diseased ant away from the colony in an effort to reduce chances of further exposure to the fungal spores near the colony.