Unexpected allies aid ants at war with “zombifying” parasite
May 4, 2012
Courtesy of Penn State University
and World Science staff
Tropical ants plagued by a parasite that turns them into “zombies” have unexpected allies in their struggle: other parasites, scientists say.
A group of “zombifying” parasites known as Ophiocordyceps are fungi that hijack ants' brains. The fungus them alters ant's brain mechanisms so that the insect marches to its death, all in an orchestrated process that facilitates the parasite's reproduction.
A dead "zombie" ant with the brain-manipulating fungus Ophiocordyceps unilateralis s.l. growing out of its head. Its stalk is in turn parasitized by another fungus, the whitish-yellow material, which scientists say castrates it. (Credit: David Hughes, Penn State U.)
But the fungal tyrant suffers oppression in turn from other fungi—which basically castrate it chemically and disrupt its reproduction, according to the researchers. The counter-parasites keep the first one in check and help prevent it from overrunning entire ant colonies.
It's truly a case where “biology is stranger than fiction,” said David Hughes of Penn State University, who led a research team that produced the findings. The research was published May 2 online in the scientific journal PLoS One.
A parasite of a parasite, called a hyperparasite, “effectively castrates the zombie-ant fungus so it cannot spread its spores,” said Hughes. This saves not a few hapless ants from a horrifying death. After commandeering their brains, the zombifying fungus makes them march to a mass ant grave near the ants' home, where it drops dead. The fungus then promptly sprouts out of the ant's head—forming a stalk from whence it spreads its fetid spores to claim more victims.
But the battle—which the researchers studied as it plays out in the Atlantic rainforests of Brazil but which also occurs in other parts of the world—isn't so simple. Far from resting easy in its cadaverous new home, the zombifying fungus falls prey to its own tormentors. These parasites spread onto its own stalk and make their home there. “Because the hyperparasitic fungi prevents the infected zombie-ant fungus from spreading spores, fewer of the ants will become zombies,” Hughes said.
As part of their research, Hughes and colleagues created a detailed model to reveal details of the interactions between the fungus-infected ants and the parasite-infected zombie-ant fungus. Scientists previously had known that ants defend their colonies against microscopic enemies such as fungal spores by efficiently grooming each other. In this study, the researchers also modeled the effect of such ant behavior on limiting infection.
“Interestingly, beyond the well-known effect of defensive ant behavior, our new research reveals the added effect of the castrating actions of the hyperparasite fungi, which may result in significantly limiting the spread of the zombie-ant fungus,” Hughes said.
The scientists report that only about 6.5 percent of the spore-producing organs of the zombie-ant fungus were viable. “Even though there are a lot of dead and infected zombie ants in the neighborhood, only a few of the spores of the zombie-ant fungus will become mature and able to infect healthy ants,” Hughes said. “Our research indicates that the danger to the ant colony is much smaller than the high density of zombie-ant cadavers in the graveyard might suggest. This complex interaction between ant colonies, their brain-manipulating parasites, and other fungi capable of lending assistance to the colony underscores the need to study social insects under natural conditions.”
May 4, 2012
Courtesy of Penn State University
and World Science staff
Tropical ants plagued by a parasite that turns them into “zombies” have unexpected allies in their struggle: other parasites, scientists say.
A group of “zombifying” parasites known as Ophiocordyceps are fungi that hijack ants' brains. The fungus them alters ant's brain mechanisms so that the insect marches to its death, all in an orchestrated process that facilitates the parasite's reproduction.
But the fungal tyrant suffers oppression in turn from other fungi—which basically castrate it chemically and disrupt its reproduction, according to the researchers. The counter-parasites keep the first one in check and help prevent it from overrunning entire ant colonies.
It's truly a case where “biology is stranger than fiction,” said David Hughes of Penn State University, who led a research team that produced the findings. The research was published May 2 online in the scientific journal PLoS One.
A parasite of a parasite, called a hyperparasite, “effectively castrates the zombie-ant fungus so it cannot spread its spores,” said Hughes. This saves not a few hapless ants from a horrifying death. After commandeering their brains, the zombifying fungus makes them march to a mass ant grave near the ants' home, where it drops dead. The fungus then promptly sprouts out of the ant's head—forming a stalk from whence it spreads its fetid spores to claim more victims.
But the battle—which the researchers studied as it plays out in the Atlantic rainforests of Brazil but which also occurs in other parts of the world—isn't so simple. Far from resting easy in its cadaverous new home, the zombifying fungus falls prey to its own tormentors. These parasites spread onto its own stalk and make their home there. “Because the hyperparasitic fungi prevents the infected zombie-ant fungus from spreading spores, fewer of the ants will become zombies,” Hughes said.
As part of their research, Hughes and colleagues created a detailed model to reveal details of the interactions between the fungus-infected ants and the parasite-infected zombie-ant fungus. Scientists previously had known that ants defend their colonies against microscopic enemies such as fungal spores by efficiently grooming each other. In this study, the researchers also modeled the effect of such ant behavior on limiting infection.
“Interestingly, beyond the well-known effect of defensive ant behavior, our new research reveals the added effect of the castrating actions of the hyperparasite fungi, which may result in significantly limiting the spread of the zombie-ant fungus,” Hughes said.
The scientists report that only about 6.5 percent of the spore-producing organs of the zombie-ant fungus were viable. “Even though there are a lot of dead and infected zombie ants in the neighborhood, only a few of the spores of the zombie-ant fungus will become mature and able to infect healthy ants,” Hughes said. “Our research indicates that the danger to the ant colony is much smaller than the high density of zombie-ant cadavers in the graveyard might suggest. This complex interaction between ant colonies, their brain-manipulating parasites, and other fungi capable of lending assistance to the colony underscores the need to study social insects under natural conditions.”
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