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.
The parasite is a tapeworm called聽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聽alters the behaviour聽of infected worker ants.
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Such ants don鈥檛 go out to forage, but instead remain in the nest, where uninfected workers care for them. 鈥淔or the infected individuals themselves it seems positive,鈥� says a member of the research team. 鈥淭hey don鈥檛 need to do anything; they鈥檙e still being fed, but what we do see is that the whole colony suffers.鈥�
Most strikingly, while normal workers die after around a year, the infected ants live for much longer. 鈥淲e鈥檝e looked at them for at least three years,鈥� she says. 鈥淎necdotally we鈥檝e heard of seven years and maybe longer.鈥�
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 鈥� the insect equivalent of blood 鈥� from ants infected with the parasite and uninfected ants. They found that the parasite releases 260 different proteins into the ants鈥� bodies. 鈥淚t鈥檚 massive 鈥� we did not expect that,鈥� 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鈥� 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鈥檛 be identified at all 鈥� they have no known equivalents in other organisms.
鈥淚 do think it鈥檚 a cool strategy,鈥� says at Harvard University, who studies 鈥渮ombie鈥� 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) (Tenebrio molitor) it infects by around a third. The parasite (Plasmodium relictum) that causes malaria in birds also of its mosquito host (Culex pipiens).
It isn鈥檛 unusual for parasites to secrete hundreds of proteins to manipulate their hosts, says Elya. Jewel wasps have been found to inject 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.
bioRxiv
