“Some other parasites do extend life spans,” Shelley Adamo, a parasite expert at Dalhousie University, in Nova Scotia, who was not involved in the study, told me. “But not like this.”
Under typical circumstances, Temnothorax ants live as most other ants do. They reside in communities ruled by a single fertile queen attended by a legion of workers whose professional lives take a predictable trajectory. They first tend the queen’s eggs as nurses, then graduate into foraging roles that take them outside the nest. Apart from the whole freaky parasite thing, “they are pretty boring,” Foitzik told me.
Normalcy goes out the door, however, when Temnothorax larvae ingest tapeworm-egg-infested bird feces trucked in by foragers. The parasites hatch and set up permanent residence in the young ants’ abdomens, where they can access a steady stream of nutrients. In return, they offer their host an unconventional renter’s fee: an extra-long life span that Foitzik and her colleagues managed to record in real time.
The researchers spent three years monitoring dozens of Temnothorax colonies in the lab, comparing the fates of workers who’d fallen prey to the parasites and those who remained infection-free. By the end of their experiment, almost every single one of the hundreds of worm-free workers had, unsurprisingly, died. But more than half the parasitized workers were still kicking—about the same proportion as the colonies’ ultra-long-lived queens. “That was amazing to see,” Biplabendu Das, an ant biologist and parasite expert at the University of Central Florida, who wasn’t involved in the study, told me. And despite their old age, the ants’ bodies still bore the hallmarks of youth. They were difficult to distinguish from uninfected nurses, who are usually the most juvenile members of the colony’s working class.
The tapeworm-laden ants didn’t just outlive their siblings, the team found. They were coddled while they did it. They spent their days lounging in their nest, performing none of the tasks expected of workers. They were groomed, fed, and carried by their siblings, often receiving more attention than even the queen—unheard of in a typical ant society—and gave absolutely nothing in return.
The deal the ants have cut with their parasites seems, at first pass, pretty cushy. Foitzik told me that her team couldn’t find any overt downsides to life as an infected ant, a finding that appears to shatter the standard paradigm of parasitism. Even the colonies as a whole remained largely intact. Workers continued to work; queens continued to lay eggs. The threads that held each Temnothorax society together seemed unmussed.
Only when the researchers took a closer look did that tapestry begin to unravel. The uninfected workers in parasitized colonies, they realized, were laboring harder. Strained by the additional burden of their wormed-up nestmates, they seemed to be shunting care away from their queen. They were dying sooner than they might have if the colonies had remained parasite-free. At the community level, the ants were exhibiting signs of stress, and the parasite’s true tax was, at last, starting to show. “The cost is in the division of labor,” Das said. The worms were tapping into not just “individual [ant] physiology, but also social interactions,” Farrah Bashey-Visser, a parasitologist at Indiana University who wasn’t involved in the study, told me.
Source : www.theatlantic.com