Ants infected by the parasite don't work, are cared for by uninfected workers and live much longer than usual.
Ants infected with a tapeworm live several times longer than usual. Exactly how the parasite extends the life of its host is unclear, but a cocktail of proteins it releases may provide some clues.
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| Temnothorax nylanderi ants may benefit from a tapeworm infection thatmacroguy/Shutterstock |
The parasite is a tapeworm called Anomotaenia brevis whose main hosts are several types of woodpecker. Ants of the species Temnothorax nylanderi sometimes collect woodpecker faeces and take them back to the nest to feed to larvae. If there are tapeworm eggs in the faeces, they hatch in the larvae guts where the parasites burrow through the gut wall and develop in the body cavity.
Researchers at Johannes Gutenberg University Mainz in Germany have been collecting infected ants from a nearby forest and studying them for decades. They have found that the tapeworm dramatically alters the behaviour of infected worker ants.
Such ants don’t go out to forage, but instead remain in the nest, where uninfected workers care for them. “For the infected individuals themselves it seems positive,” says Juliane Hartke, a member of the research team. “They don’t need to do anything; they’re still being fed, but what we do see is that the whole colony suffers.”
Most strikingly, while normal workers die after around a year, the infected ants live for much longer. “We’ve looked at them for at least three years,” she says. “Anecdotally we’ve heard of seven years and maybe longer.”
This benefits the parasite because even if it is several years before a woodpecker discovers an infected ant nest, some ants will still carry the parasite and infect the woodpecker if it eats them, completing the life cycle.
In their latest study, Hartke and her colleagues analysed haemolymph – the insect equivalent of blood – from ants infected with the parasite and uninfected ants. They found that the parasite releases 260 different proteins into the ants’ bodies. “It’s massive – we did not expect that,” she says.
Two of the most abundant parasite proteins were the antioxidants superoxide dismutase and thioredoxin peroxidase. However, it is possible that these substances are released to protect the parasites from ant defences, says Hartke, rather than being the cause of the ants’ longer lives. And in people at least, researchers have failed to find evidence that extra antioxidants delay ageing.
Most of the other proteins secreted by the parasites couldn’t be identified at all – they have no known equivalents in other organisms.
“I do think it’s a cool strategy,” says Carolyn Elya at Harvard University, who studies “zombie” funguses that manipulate the behaviour of insects. There are a few other examples of parasites extending lifespans, says Elya, though not by nearly the same extent.
Another tapeworm (Hymenolepis diminuta) extends the lifespan of a beetle (Tenebrio molitor) it infects by around a third. The parasite (Plasmodium relictum) that causes malaria in birds also slightly increases the lifespan of its mosquito host (Culex pipiens).
It isn’t unusual for parasites to secrete hundreds of proteins to manipulate their hosts, says Elya. Jewel wasps have been found to inject a cocktail of 264 proteins into their host.
Hartke now plans to try to find out what all the unidentified proteins released by A. brevis do to the ant. This might reveal more definitively how to make ants live longer, she says, but is unlikely to have any relevance to people.
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