(Inside Science) -- Ants can form colonies reminiscent of complex human societies, divvying up labor between specialized castes such as fertile queens and sterile workers. Now scientists investigating ants that can naturally clone themselves are shedding light on how such division of labor might have evolved, yielding insights on how group behavior emerges.
Anyone witnessing the way children fight over toys may be reminded of how nature is often described as "red in tooth and claw." The fact that competition drives much behavior in the wild then raises questions of how cooperation between individuals might have evolved in the first place.
"Why similar individuals join in groups is an important and nontrivial question, because one would assume that, at least initially, such individuals should compete over resources, rather than divide tasks and complement each other," said study senior author Daniel Kronauer, an evolutionary biologist at Rockefeller University in New York.
To learn more about the evolution of group behavior, Kronauer and his colleagues experimented with the clonal raider ant (Ooceraea biroi), which is native to the Asian mainland and raids the nests of other ant species to feed on their young. Unlike many other ants, this species has no queens -- instead, each ant lays eggs that are clones of itself. Since all of the clonal raider ants are workers, the scientists reasoned that this species may resemble the solitary ancestors of ants, and could thus shed light on how division of labor evolved among these insects.
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The scientists painted each ant with unique identifying marks and used 32 digital cameras and motion-tracking software to watch 112 ant colonies simultaneously. Each colony had one to 16 ants that were all identical in terms of genetics and age. Over roughly 40 days, they monitored how the ants behaved during their reproductive phase, when all the insects remain inside the nest and lay eggs, and their brood-care phase, when the ants took care of their young inside the nest but also left the nest to, for instance, forage or dispose of waste.
The researchers found that in colonies with as few as six ants, division of labor could emerge -- instead of alternating between leaving and staying in the nest, some ants appeared to prefer one set of tasks over the other. As colonies grew in the number of their ants, the activities of the insects grew more specialized and the behaviors seen in the colonies grew more diverse.
In addition, the researchers noted that increasing colony size led to far more stable conditions inside nests. This in turn boosted overall colony fitness in terms of factors such as survival rates and reproduction levels.
"We show that even small groups of extremely similar individuals can do much better than individuals by themselves, and that division of labor can emerge in a self-organized manner pretty much immediately," Kronauer said. "That's not necessarily what I would have expected, and it implies that group living might evolve fairly readily, rather than constitute a major barrier that evolution can rarely overcome."
The benefits that group behavior have even on relatively tiny scales might help explain how large complex groups can evolve in the first place. "This work shows that emergent division of labor indeed affects fitness in a controlled experimental context, and that group size is a critical part of it," said behavioral ecologist Jennifer Fewell at Arizona State University in Tempe, who did not take part in this research. "It is a powerful demonstration of the importance of division of labor, and of self-organizational effects more generally on individual and group success."
Kronauer and his colleagues now plan to see what happens if they make the genetics and ages of ants in each colony more diverse. "People have argued that that should be beneficial -- for example, because more heterogeneous groups might be more efficient at dividing labor," Kronauer said. "But let's see whether that's really the case."
The scientists detailed their findings online August 22 in the journal Nature.