What is it about?
In many animals the aging process is familiar: as we get older our chance of dying increases and our reproductive rate declines. However, some organisms reverse this pattern. In a number of plants and fish, in some marine invertebrates and in a few terrestrial vertebrates, the chance of dying decreases with age and the reproductive rate increases. This pattern is known as negative senescence. In a 34 year study of survival and reproduction in more that 3000 colonies of the western harvester ant, Pogonomyrmex occidentalis, we show that these ants also have negative senescence. With growth continuing throughout their life, larger colonies have lower mortality rates and greater reproductive rates.
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Photo by Jonathan Gagnon on Unsplash
Why is it important?
Because the trajectory of senescence is reversed, one can ask why both survival and reproduction increase with age. Virtually all organisms that have reversed aging also have indeterminate growth–they continue to grow throughout their life. Larger individuals are more protected from predators and other sources of mortality and usually have increased reproductive capacity. Ant colonies also have indeterminate growth. In contrast to trees or rockfish whose body size increases with age, an ant colony grows by adding more individuals to the social group. It is the colony, not individual ants, that has indeterminate growth and which shows negative senescence. Colonies of the western harvester ant function as superorganisms. The workers are the soma, or body, of this superorganism. Worker ants cannot reproduce; they do all the labor in the colony: foraging, caring for the young, and defending the nest. The single queen’s sole function is reproduction. Workers live approximately a year, and are replaced when they die. Unlike a fish or turtle which must have mechanisms that prevent or repair damage to their aging soma, that of the superorganism never grows older. The extreme division of labor found only in highly social superorganisms is a unique pathway to reverse aging.
Perspectives
When we began this study, we knew essentially nothing about the demography of harvester ants. We did not know how long individual colonies could live, although we did have access to some old aerial photographs of our site, which showed that some colonies had been present for at least 20 years. As data accumulated, we began to realize that their pattern of aging was unusual. That led us to start looking at how colony growth, survival, and reproduction were related. One of the thrilling features of science is recognizing similarities in widely disparate species. Our work shows that harvester ants have acquired the traits critical to negative senescence but by very different means and at a different level of biological organization.
Blaine Cole
University of Houston
Read the Original
This page is a summary of: A replaceable soma enables negative senescence in harvester ants, Proceedings of the National Academy of Sciences, November 2026, Proceedings of the National Academy of Sciences,
DOI: 10.1073/pnas.2612817123.
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