Zombie Ants From Fungus On Brain [OA]

[Darwinsbulldog]

OA = OPEN ACCESS

Hughes, D., S. Andersen, et al. (2011). "Behavioral mechanisms and morphological symptoms of zombie ants dying from fungal infection." BMC Ecology 11(1): 13.

BACKGROUND:Parasites that manipulate host behavior can provide prominent examples of extended phenotypes: parasite genomes controlling host behavior. Here we focus on one of the most dramatic examples of behavioral manipulation, the death grip of ants infected by Ophiocordyceps fungi. We studied the interaction between O. unilateralis s.l. and its host ant Camponotus leonardi in a Thai rainforest, where infected ants descend from their canopy nests down to understory vegetation to bite into abaxial leaf veins before dying. Host mortality is concentrated in patches (graveyards) where ants die on sapling leaves ca. 25 cm above the soil surface where conditions for parasite development are optimal. Here we address whether the sequence of ant behaviors leading to the final death grip can also be interpreted as parasite adaptations and describe some of the morphological changes inside the heads of infected workers that mediate the expression of the death grip phenotype.RESULTS:We found that infected ants behave as zombies and display predictable stereotypical behaviors of random rather than directional walking, and of repeated convulsions that make them fall down and thus precludes returning to the canopy. Transitions from erratic wandering to death grips on a leaf vein were abrupt and synchronized around solar noon. We show that the mandibles of ants penetrate deeply into vein tissue and that this is accompanied by extensive atrophy of the mandibular muscles. This lock-jaw means the ant will remain attached to the leaf after death. We further present histological data to show that a high density of single celled stages of the parasite within the head capsule of dying ants are likely to be responsible for this muscular atrophy. CONCLUSIONS:Extended phenotypes in ants induced by fungal infections are a complex example of behavioral manipulation requiring coordinated changes of host behavior and morphology. Future work should address the genetic basis of such extended phenotypes.

http://www.biomedcentral.com/content...6785-11-13.pdf
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Science Daily's Commentary:-

ScienceDaily (May 9, 2011) — New research has revealed how infection by a parasitic fungus dramatically changes the behavior of tropical of carpenter ants (species Camponotus leonardi), causing them to become zombie-like and to die at a spot that has optimal reproduction conditions for the fungus. The multinational research team studied ants living high up in the rainforest canopy in Thailand.
A paper describing the research will be published in the BioMed Central open-access journal BMC Ecology on 9 May 2011.
"The behavior of these infected zombie ants essentially causes their bodies to become an extension of the fungus's own phenotype, as non-infected ants never behave in this way," said David P. Hughes, the first author of the research paper and an assistant professor of entomology and biology at Penn State University.
Using transmission-electron and light microscopes, the researchers were able to look inside the ant in order to determine the effect of the fungus on the ant. They found that the growing fungus fills the ant's body and head, causing muscles to atrophy and forcing muscle fibres to spread apart. The fungus also affects the ant's central nervous system. The scientists observed that, while normal worker ants rarely left the trail, zombie ants walked in a random manner, unable to find their way home. The ants also suffered convulsions, which caused them to fall to the ground. Once on the ground, the ants were unable to find their way back to the canopy and remained at the lower, leafy understory area which, at about 9 or 10 inches (25 cm) above the soil, was cooler and moister than the canopy, provided ideal conditions for the fungus to thrive.
The scientists found that at solar noon, when the Sun is at its strongest, the fungus synchronised ant behavior, forcing infected ants to bite the main vein on the underside of a leaf. The multiplying fungal cells in the ant's head cause fibres within the muscles that open and close the ant's mandibles to become detached, causing "lock jaw," which makes an infected ant unable to release the leaf, even after death. A few days later, the fungus grows through the ant's head a fruiting body, a stroma, which releases spores to be picked up by another wandering ant.
"The fungus attacks the ants on two fronts: first by using the ant as a walking food source, and second by damaging muscle and the ant's central nervous system," Hughes said. "The result for the ant is zombie walking and the death bite, which place the ant in the cool, damp understory. Together these events provide the perfect environment for fungal growth and reproduction."

http://www.sciencedaily.com/releases...0509065536.htm