Fire ants in the U.S.A.
In the 1970s, scientists discovered a new and more threatening form of S. invicta in Mississippi. Each of these colonies supported multiple queens. The multiple queen form called polygyne ("poly" = many, "gyne" = female) poses a greater hazard than the single queen form called monogyne ("mono" = one). The tightly-packed, multiple-queen colonies drive out native ant species and other animals. Today, multiple-queen colonies dominate Texas, and may be ready to spread throughout the country.
Both multiple- and single-queen colonies thrive in Argentina, but the ants there don't seem to take over as they have in Texas where, in some places, you could hopscotch across a field, landing only on ant nests. Let's take a look at how natural selection might favor colonies with different numbers of queens, how genes can influence queen number, and how that knowledge might help us slow the S. invicta invasion.
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Fire ant worker's head courtesy of USDA APHIS PPQ Imported Fire Ant Station Archives, www.forestryimages.org.
Understanding Evolution © 2015 by The University of California Museum of Paleontology, Berkeley, and the Regents of the University of California