Sex, Ants, and Speciation

The sex life of fire ants has shed light on how new species may arise, according to a report in the 17 October issue of Nature.

If populations are isolated geographically from one another, they can eventually evolve into several new species. Biologists have speculated that restrictive mating practices can also isolate populations and trigger speciation. Now a team led by Kenneth G. Ross, an entomologist at the University of Georgia, Athens, offers evidence for the process in fire ants.

Analyzing DNA from 100 different colonies, Ross's team found an unusual pattern of gene flow from one generation to the next. They found that male ants from monogynous colonies--those ruled by a single queen--could mate with queens from monogynous and polygynous colonies. Few males from polygynous colonies, on the other hand, are fertile, and those that are appear to mate only with polygynous queens. This mating pattern forces a one-way gene flow from monogynous to polygynous colonies.

"It's logical ... to think that this might cause a complete absence of gene flow" to monogynous colonies, Ross says. The result is a genetic barrier that could be as effective as any geographic division in isolating the monogynous colonies, allowing them to evolve into a new species over millennia. "We're excited about this because it can be used to explain a number of other instances" of closely related species of ants, bees, and other social insects, says geneticist Ross H. Crozier of La Trobe University in Australia.