Making decisions is hard. Making collective decisions is harder. Think about how hard it would be to decide where to buy a house. Then think about how hard it would be to decide where to buy a house with several hundred roommates. As unmanageable as that sounds a new study shows that ant colonies are able to do just that.
Taka Sasaki and Stephen C. Pratt of the School of Life Sciences and Center for Social Dynamics at Arizona State University found that ant colonies are able to prioritize certain characteristics when choosing nest sites in order to make a collective decision of where to live. Their findings were published in Biology Letters last month.
Sasaki and Pratt have extensively studied collective behavior in many different insects, including ants. Sasaki wrote in an email to The News-Letter, “Some people think that ants are not that smart and simply respond to stimuli in their current environment,” He continued, “However, many studies actually have shown that they are cognitively very sophisticated even though they have very tiny brains! We were wondering if ants were able to change weights of attributes according to their experience, like humans do.”
“We found that ant colonies alter their weighting of different nest site features based on the array of options they have previously experienced,” Sasaki said. Sasaki and Pratt’s experiment differs from any previously conducted animal behavior research. “Past research has mainly focused on a single attribute at a time, testing whether animals change their selectivity according to the average quality of options available in their environment,” Sasaki wrote. “We instead created an environment where two attributes differed in how well they distinguished options, and showed that colonies came to rely more on the more informative feature.”
Sasaki and Pratt tested the ability of ants to make prioritized decisions by performing a series of tests on ant colonies in choosing nesting sites. First all of the ants needed to be identified. “To identify ants, we paint each ant with unique colors,” Sasaki explained. “As the ant is very small (2-3 mm), it is initially very difficult to do. But as you do it more,
See PRIORITIES, page B8
it surprisingly becomes easier.”
Temnothorax rugatulus, the ant species used in the experiment, has a strong preference for nests with smaller entrances and darker interiors. Initially the ant colonies were offered a choice between Nests E and L. Nest E had a smaller entrance than Nest L, but Nest L had a darker interior than Nest E, posing a trade-off between the two considered attributes: entrance size and interior lighting.
Next the ant colonies were divided into two groups and subject to a series of four trials. The “entrance treatment” group had to move from a standard home nest and choose between moving to either a new standard nest or to one that had a larger entrance but was otherwise identical to the standard nest. On the other hand the “light treatment” group had to move from a standard home nest and choose between moving to either a new standard nest or to one that had a brighter interior but was otherwise identical to the standard nest. In each trial the ant colonies in both treatment groups usually moved to the new standard home nest.
In order to determine whether the experiences the ants underwent during the treatments had changed their weighting of the two attributes, all of the ant colonies were again presented with the initial choice between Nest E and Nest L. Colonies that received the entrance treatment tended to prefer Nest E over L, prioritizing smaller entrances over darker interiors.
Conversely colonies that received the light treatment tended to prefer Nest L over E, prioritizing darker interiors over smaller entrances. The ant colonies shifted their preferences based on their previous experiences.
Sasaki and Pratt’s findings have forged new paths in the understanding of animal behavior. “As far as we know, this is the first study to show that animal groups, like individuals, change decision-making strategies according to experience,” Sasaki wrote. “[It] is interesting that animals with tiny brains can collectively do something that we do. Like neurons in a brain, ants interact with each other to achieve sophisticated cognition.”
For Sasaki and Pratt, however, several questions remain unanswered. “We still do not know the mechanisms of this collective cognition,” Sasaki wrote. “For example, how do [ants] share information? Is it always beneficial to share information?”
Sasaki and Pratt have high hopes for future research in the decision making behavior of animals. “We also hope that other researchers who work on different organisms can use this (neuron in a brain) paradigm to test how experience affects decision-making processes,” Sasaki wrote, “For example, some researchers (also good friends of mine) study decision making of slime molds. I wonder if slime molds can change their weights of attributes according to experience even though they do not have a brain!!”
Perhaps through this study, we can learn from ants how to better cooperate with one another when making decisions as a group.
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