Scientist Reveals the Reproductive Function of a Harvest Ant Dynasty

Harvester ant collectors wait in the nest. Biology professor Deborah Gordon studies reproductive trends in wild ant colonies. Credit: Katherine Dektar

Ants are just about everywhere you look, and yet it’s largely unknown how they manage to be so ubiquitous. Scientists have understood the carnal mechanism of ant reproduction, but until now have known little about how successful a colony’s daughters are when trying to establish new colonies.

For the first time, Stanford biologists have been able to identify specific parent ants and their own children in wild ant colonies, making it possible to study reproductive trends.

And in a remarkable display of longevity, an original queen ant was found to produce new ants several decades after mating, sending out daughter queens during her 20- to 30-year lifespan.

“Most animals produce offspring for a while, and then they get to a life stage where they don’t,” Gordon said. “These queen ants mate once, store that sperm in a special sac, keep it alive and use it to fertilize eggs for another 25 years.”

From an ecological point of view, an ant colony is very similar to a tree that releases seeds, with the potential to create new trees. A queen ant produces genetically identical worker ants that live in the same colony, and also produces sons and daughter queens. The daughter queens establish new colonies after mating.

Deborah Gordon, a biology professor at Stanford and a senior fellow at the Stanford Woods Institute for the Environment, has been studying a particular population of harvest ant colonies in southeastern Arizona for 28 years, meticulously recording when a new colony comes up or an older one falls.

Gordon’s group took the DNA fingerprint of each colony by analyzing a piece of microsatellite, or “junk,” DNA to determine which colonies were related. By linking the genetic analysis to the long-term observations, Gordon was able to determine the original queen and colony, and the order in which the daughter queens and subsequent generations established new colonies.

The researchers also found that only about 25 percent of the colonies reproduce at all, and many of the daughter queens are unsuccessful. The entire population — the study group was made up of about 300 colonies — relies on just a few queens to make the bulk of the offspring year after year.

“We don’t know if all harvest ant populations always behave like this, or if these trends are true for all 11,000 ant species, because no one has identified colony progeny before,” Gordon said. “This gives us new insight into how ant populations change over time.”

In general, ants play an important role in agriculture around the world, with some helping to spread seeds while others eating herbivorous insects. Understanding how populations of ant colonies reproduce and expand, and the rate at which they do so, could be helpful in controlling invasive ant species, predicting crop yields, and understanding the ecology of tropical forests.

“If you’re trying to understand how a population grows — let’s say you’re trying to maintain a population of lions — the first thing you need to know is how many lionesses you have and how many cubs they have and can support per year,” Gordon said. . “For ecological purposes it is very useful to be able to say how ant populations will grow. This is the first step in understanding how to predict the number of ant colonies.”

The study was published on January 31 in the online version of the Journal of Animal Ecology.

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