Entomologists Discover Florida Fire Ant Matriarchy

In most colonies, ants work in the service of a single reproductive queen, but that’s not always the way ant communities function.

Researchers at the University of Georgia have found colonies of tropical fire ants, native to Florida and the coast of Georgia, that thrive with multiple queens and in close proximity to single-queen colonies of the same species.

“The coexistence of two dramatically different social structures fascinated me,” Kip Lacy said. “I needed to know more.”

Lacy, who is currently a graduate fellow at Rockefeller University but received his master’s degree in entomology from UGA’s College of Agricultural and Environmental Sciences in 2018, collaborated with UGA fire ant researcher Ken Ross and DeWayne Shoemaker at the University of Tennessee, to isolate and document colonies with multiple queens.

Their work will appear in the April 2019 issue of Current Biology.

Lacy worked with colleagues at the U.S. Department of Agriculture Agricultural Research Service in Gainesville, Florida, to help locate and isolate the communities of native fire ants that cover the shoulders and medians of Florida highways.

In these areas, they found that multi-queen “polygyne” colonies would nest right next to single-queen monogyne colonies of the same species. Nests with single queens were found just 1.5 meters away from nests with as many as 13 queens, Lacy said.

“They can coexist, but their social structure remains intact,” Lacy said.

Many fire ant colonies are founded by a single queen, mated with a male ant from another colony, who produces all the eggs to establish a colony of their own. However, it is not unheard of for ants of the same species to develop alternative reproductive habits.

Ross, who has studied the genetics and social structures of fire ants for decades, previously documented the coexistence of monogynous and polygynous colonies in populations of invasive red imported fire ants in Georgia. In polygynous colonies of this species, all ants share a “social chromosome” that is absent from individuals in single-queen colonies. This chromosome apparently causes what Ross described as the “polygynous syndrome.”

In addition to the number of queens, polygynous colonies of the red imported fire ant differ from monogynous colonies in many respects, including lower levels of aggressiveness toward non-nestmates and smaller body sizes of individual ants. But despite these differences, the basic mode of reproduction in both types of colonies is the same – all daughters (both queens and workers) are reproduced sexually.

Lacy was surprised to find that the reproductive modes of the two species of colonies in the tropical fire ant were different. Like the red imported fire ants, queens of monogynous colonies produce all daughters sexually. In contrast, in multi-queen tropical fire ant colonies, Lacy found that the queens reproduce asexually. All reproductive queens and daughter queens in the colony have been shown to be genetically identical.

However, the worker ants in these colonies showed much greater genetic diversity; unlike the queens, they were not clones. Controlled experiments revealed that queens were produced asexually and workers were produced sexually in polygynous colonies.

“That was a surprise because we also found that the male ants in these colonies appear to be sterile,” Lacy said.

Lacy and Ross found that queens from multi-queen colonies mated with males from single-queen colonies. This practice helped facilitate clonality in multi-queen colonies by introducing new genetic material into the colony to maintain genetic diversity, but there is no apparent benefit to the male ants.

“(Evolutionarily speaking) the males get nothing out of it because their sperm starts producing workers that are sterile,” Ross said. “The genetic lines of those men end there.”

Lacy and Ross have described the behavior of polygynous queens as “sperm parasitism.”

“Different species of ants have previously exhibited different forms of social parasitism, and this is just one more example of that behavior,” Ross said.

The genetic underpinnings of asexuality and multi-queen syndrome in the tropical fire ant are currently unknown. However, genetic studies suggest that asexual queens may have evolved from sexually reproducing queens in monogynous colonies.

It is important to know more about the biology of the tropical fire ants because although they have been displaced by invasive fire ants in some communities in the coastal regions of Georgia and Florida, they have become invasive pests in Africa, Southeast Asia and even the Galapagos. Islands.

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