In comparison to workers, queen ants live much longer. What their longevity secrets could entail for ageing in other species is being discovered by researchers.
Animals that breed frequently typically live short lives, whereas less productive animals typically live longer. Cockroaches have a lifespan of less than a year and can lay hundreds of eggs. In their first year or two of life, mice give birth to dozens of young. Only one calf is born to a humpback whale every two to three years, and they have long lifespans. The adage appears to reflect evolutionary tactics that direct nutritional resources either toward hasty reproduction or toward developing greater robustness for a long-term advantage.
Ant queens, however, can have it all. In certain ant species, queens lay thousands upon thousands of eggs, which develop into all the workers in the nest, over the course of more than 30 years. Female worker ants, who are sterile, live only a few months in contrast. However, if the situation calls for it, certain species’ workers can step up and take on the role of pseudo-queens for the benefit of the nest, extending their lives significantly in the process.
Although the factors that cause such a wide variety in ant life spans remain poorly understood, two recent studies have provided crucial information. New York University researchers discovered that some ant queens create a protein that inhibits insulin’s ability to age cells, allowing them to ingest all the extra food required for egg-laying without suffering any life-shortening consequences.
A parasite that significantly extends the lives of its ant hosts by secreting a potent mix of antioxidants and other substances was recently revealed by German researchers. Both results provide more proof that genetic restrictions have no effect on the observed life lengths of species.
“Most studies about aging are done on model organisms which have very short life spans,” said Laurent Keller, a professor of ecology and evolution at the University of Lausanne in Switzerland. Social insects, he explained, offer fascinating opportunities to study the importance of gene expression in aging because the queen and the workers in a colony often have the same genome but differ in their life spans by an order of magnitude.Two decades ago, Keller showed that ant queens live about 100 times as long as the ancestral solitary insects from which ants evolved.
Eating More and Aging Slower
Insulin and the molecular signalling system that it stimulates have been identified as important ageing regulators by studies for many years. Insulin has a major impact on the amount of energy available to cells for growth, reproduction, and repair because it regulates how body cells absorb and utilise the sugar glucose. In the process, it controls the production of oxidising molecules such as free radicals and other potentially dangerous metabolic byproducts. Many scientists believe that this is the reason why calorie-restricted diets, which keep insulin levels low, appear to increase life expectancy in a variety of species.
Moreover, insulin seems to have added significance for ants. Several years ago, work led by the evolutionary biologist Daniel Kronauer at Rockefeller University showed that changes in how ants respond to insulin seem to have coaxed them to evolve altruistic colonial societies with reproductive queens and nonreproductive workers.
In light of this, Vikram Chandra had insulin on his mind four years ago while he was a PhD student at Rockefeller University researching the distinctions between ant queens and workers. ‘Ingrid Fetter-Pruneda, a postdoctoral fellow in the lab at the time, and he co-led a team that examined gene expression in seven ant species and came to the conclusion that the queen’s brains experienced more insulin signalling than the workers’. Insulin injections into worker ants stimulated egg development by reawakening latent ovaries.These results demonstrated that insulin signalling induced the ants to become reproductive, according to Kronauer, who directed the study.
That discovery laid the foundation for new work conducted as part of a long-term collaboration between the biologists Claude Desplan and Danny Reinberg at New York University. They showed that evolution has rewired some components of the insulin signaling pathway in ants in ways that could explain why the queens live longer.
The Parasite That Lengthens Life
In a strange twist, nature seems to have already run its own version of a similar experiment in another species. Researchers in Germany recently discovered that a parasitic tapeworm has evolved the ability to manipulate the extreme plasticity of ant life spans to its own advantage.
The tapeworm must spend part of its life inside acorn ants (Temnothorax nylanderi), which get their names from the nests they build inside individual acorns. When the workers go out to forage, they sometimes eat a tapeworm egg and get infected. But to complete its life cycle, the tapeworm also needs to infect a woodpecker, and it gets that opportunity when woodpeckers eat the acorn homes of the ants.
The odd discovery was made by Sara Beros, a student in Susanne Foitzik’s lab at the Johannes Gutenberg University of Mainz in Germany, when she opened some acorn ant nests a few years ago. All the uninfected workers had perished during their months of observation, but the infected ones had not. Because they change from brown to yellow, the parasitized ants are simple to spot. Foitzik recalled thinking,
“That’s not possible,” when Beros first informed him about it. Nothing survives. Beros insisted still, “and so we thoroughly investigated it.”
In work presented last summer at a meeting of the International Union for the Study of Social Insects and posted just before Christmas on the biorxiv.org preprint server, Foitzik’s team showed that during the tapeworm’s larval stage in ants, it pumps proteins into the ant’s equivalent of blood (hemolymph) that dramatically extend the life span of the worker. Unlike the Indian jumping ants, acorn ants do not normally develop into gamergates, so the parasite’s extension of their lives has no natural precedent.“The effect is super strong,” Kronauer said. During the three-year experiment, infected workers lived five times as long as uninfected ones and showed mortality rates as low as those of the queens. The parasite’s manipulation extended the life span of workers so much “that basically you can’t distinguish it from a queen’s,” he said