A small number of species show few or no apparent signs of age-related degeneration across near all of a life span, such as lobsters, naked mole rats, urchins, and so forth. This phenomenon is known as negligible senescence and is of considerable interest to the life science community. Here, researchers provide evidence for an ant species to be negligibly senescent:
Once quick and strong, both body and mind eventually break down as aging takes its toll. Except, it seems, for at least one species of ant. Pheidole dentata, a native of the southeastern U.S., isn't immortal. But scientists have found that it doesn't seem to show any signs of aging. Old worker ants can take care of infants, forage and attack prey just as well as the youngsters, and their brains appear just as sharp. "We really get a picture that these ants - throughout much of the lifespan that we measured, which is probably longer than the lifespan under natural conditions - really don't decline." Such age-defying feats are rare in the animal kingdom. Naked mole rats can live for almost 30 years and stay spry for nearly their entire lives. They can still reproduce even when old, and they never get cancer. But the vast majority of animals deteriorate with age just like people do.
In the lab, P. dentata worker ants typically live for around 140 days. Researchers focused on ants at four age ranges: 20 to 22 days, 45 to 47 days, 95 to 97 days and 120 to 122 days. Unlike previous studies, which only estimated how old the ants were, this work tracked the ants from the time the pupae became adults, so researchers knew their exact ages when putting them through a gamut of tests. The researchers expected the older ants to perform poorly in all these tasks. But the elderly insects were all good caretakers and trail-followers - the 95-day-old ants could track the scent even longer than their younger counterparts. They all responded to light well, and the older ants were more active. Ants of all ages attacked fruit flies with the same level of aggressiveness, flaring their mandibles or pulling at the fly's legs.
Then the researchers compared the brains of 20-day-old and 95-day-old ants, identifying any cells that were on the verge of dying. They saw no major differences with age, nor was there any difference in the location of the dying cells, showing that age didn't seem to affect specific brain functions. Ants and other insects have structures in their brains called mushroom bodies, which are important for processing information, learning and memory. The researchers also wanted to see if aging affects the density of synaptic complexes within these structures - regions where neurons come together. Again, the answer was no. The old ants didn't experience any drop in serotonin or dopamine levels either, two brain chemicals whose decline often coincides with aging.