A surprising new study has revealed that parasitic infections can extend the life expectancy of worker ants, possibly by slowing down the aging process. The experts report that ants of the species Temnothorax nylanderi infected with a tapeworm live much longer than other worker ants in the same colony.
“The lifespan of the infected ants is significantly prolonged. According to our observations, such workers have a survival rate similar to that of queens,” said Professor Susanne Foitzik of Johannes Gutenberg University Mainz (JGU), who led the research.
According to the researchers, possible explanations for the extended lifespan observed in worker ants may be linked to changes in their physiology caused by the parasites, or to the enhanced care they receive in the nest.
Some ant queens can survive for several decades, spending almost all of their life tucked away safely in the nest where they are cared for by the workers. By contrast, worker ants live for only for weeks or months, progressing to risky jobs outside of the colony as they grow older, such as foraging for food.
Queens of the species T. nylanderi can live for up to 20 years, but it is rare for their female workers to reach the age of two. Ant queens live longer thanks to the high levels of social care they receive, a safe environment, and the activation of physiological repair mechanisms. These same factors may actually contribute to the extremely high survival rates of T. nylanderi worker ants with a certain tapeworm infection.
The ants described in the study form small colonies on the forest floor inside of acorns or wooden branches. The insects serve as an intermediate host for the tapeworm Anomotaenia brevis. A single ant can be infected by up to 70 parasitic larvae, which survive in the body fluid.
The research team investigated the long-term consequences of the parasitic infection by collecting ant colonies from forests around Mainz and observing them in the laboratory.
“We tracked the survival rate of the workers and queens in both infected and uninfected ant colonies over three years, until more than 95 percent of the uninfected workers had died,” explained Professor Foitzik.
At that point, over half of the infected workers were still alive. Their survival rate was practically identical to that of long-lived queens.
“It is quite extraordinary that a parasite can trigger such a positive change in its host. This lifespan extension is very unusual.”
The infected workers turn a light yellow color that makes them easy to distinguish from their brown nest-mates. The ants with parasites are also less active, and receive care from other workers in the nest.
“The infected insects get more attention and are fed, cleaned, and looked after better. They even benefit from slightly more care than the nest’s queen,” explained Professor Foitzik.
Remarkably, the infected ants were found to have metabolic rates and lipid levels similar to those of younger ants, suggesting that they remain in a permanent juvenile stage as a result of the parasitic infection. According to the experts, this is likely because the tapeworm larvae alter the expression of ant genes that affect aging, and also due to parasites’ release of proteins containing antioxidants.
The researchers found no evidence that the insects actively beg for enhanced care. However, chemical signals on the cuticle of infected ants were found to elicit more attention from their nest-mates.
“The infected insects live a life of luxury, but the fact that they receive more social care cannot alone account for their prolonged lifespan,” concluded Foitzik.
The study is published in the journal Royal Society Open Science.