Parasite grants ants "eternal youth" – but there's a dark side
Eternal youth is the first thing many of us might wish for if we stumbled onto a genie or a magic monkey’s paw, but there’s always a catch. Now, scientists have discovered a version of this story playing out in ant nests, as parasites drastically extend the lifespan of worker ants – at a terrible cost.
By definition, parasites are bad news for the host, competing for nutrients or other resources. But at first glance, that didn’t seem to be the case for the relationship between Temnothorax nylanderi, ants and Anomotaenia brevis tapeworms. The parasites live in the ants’ guts, where they seem to bestow their hosts with much longer lifespans than uninfected ants.
To investigate what’s going on, researchers at Johannes Gutenberg University Mainz watched 58 colonies of the ants for three years, some infected with the parasites and some without. By the end of that period, none of the original uninfected worker ants were still alive – but about 53 percent of the infected insects were. The upper limit for how long they could live remains unknown, due to the length of the study, but the trend so far seems to put them about on par with queens, which are known to survive for up to 20 years.
Even at their advanced age, the infected ants still retained their youthful bodies. Young ants start off a yellow color, usually turning brown as they age and their skin hardens – but infected ants stayed yellow.
And the deal gets even cushier. Infected ants were far less active than usual, never leaving the nest or chipping in to help with any of the usual tasks. Instead, they lazed around the nest while their uninfected colony-mates fed them, groomed them and even carried them around. In some cases, they were attracting more attention than the queen herself.
And that’s where the dark downside creeps in. It seems like a pretty sweet gig for the individual infected insects, but the colonies as a whole began to suffer. Uninfected ants appeared to be more stressed out and were dying younger than they might have if the parasites didn’t show up at all.
There’s also the question of what’s in it for the worms themselves, and the team found that the parasites are playing the long game by keeping the infected ants coddled and lazy. It’s only a matter of time before a woodpecker comes knocking on the nest, and while healthy ants will scatter, the infected ones just sit there and await their fate.
The endgame is that these worms reproduce inside the woodpecker’s gut. The birds poop out the tapeworm eggs, where ant foragers will stumble onto them and feed them to their young in the nest, starting the cycle over anew.
On closer inspection, the team found some metabolic changes in infected ants that drive this biology and behavior. When worker ants are “promoted” to queens, certain genes switch on that boost their lifespan – and the worms also seem to be able to turn these on in their hosts. Infected ants also give off unique chemical signals – the main method of communication between ants – that drive their broodmates to want to look after them.
All up, it’s another fascinating example of the kind of microscale drama and intrigue we might be walking past on a daily basis. Insidious as it is, this story sounds a bit less horrifying than the fungus that turns ants into zombies.
The research was published in the journal Royal Society Open Science.