Temperatures are rising and one ant colony will soon have to make a collective decision. Each ant feels the rising heat under its feet, but just keeps going until the ants suddenly change course. The whole group rushes out as one – it has been decided to evacuate. It’s almost as if the ant colony has a larger, collective mind.
A new study suggests that ants as a group are indeed similar to networks of neurons in the brain.
Rockefeller’s Daniel Kronauer and postdoctoral associate Asaf Gal developed a new experimental setup to closely analyze decision-making in ant colonies. As reported in the Proceedings of the National Academy of Sciencesthey found that when a colony evacuates due to rising temperatures, its decision is a function of both the magnitude of the heat increase and the size of the ant group.
The findings suggest that ants combine sensory information with the parameters of their group to arrive at a group response — a process similar to neural calculations that give rise to decisions.
“We’ve pioneered the understanding of the ant colony as a cognitive-like system that senses inputs and then translates them into behavioral outputs,” said Kronauer, head of the Laboratory of Social Evolution and Behavior. “This is one of the first steps to really understanding how insect communities engage in collective computation.”
A new paradigm
At the most basic level, decision making comes down to a series of calculations designed to maximize benefits and minimize costs. For example, in a common type of decision making called sensory response thresholding, an animal must detect sensory input such as heat above a certain level in order to produce a certain expensive behavior, such as walking away. If the temperature rise isn’t big enough, it’s not worth it.
Kronauer and Gal wanted to investigate how this kind of information processing takes place at the collective level, where group dynamics play a role. They developed a system that allowed them to precisely disrupt an ant colony with controlled temperature rises. To track the behavioral responses of individual ants and the entire colony, they marked each insect with different colored dots and tracked their movements with a tracking camera.
As the researchers expected, fixed-size colonies of 36 workers and 18 larvae reliably evacuated their nests when temperatures hit 34 degrees Celsius. This finding makes intuitive sense, Kronauer says, because “if you feel too uncomfortable, leave.”
However, the researchers were surprised to find that the ants weren’t just reacting to the temperature itself. When they increased the colony from 10 to 200 individuals, the temperature needed to make the decision to leave increased. For example, colonies of 200 individuals held out until temperatures rose above 36 degrees. “It seems that the threshold is not fixed. Rather, it is an emerging trait that changes with group size,” says Kronauer.
Individual ants are unaware of the size of their colony, so how could their decision depend on it? He and Gal suspect the explanation has to do with the way pheromones, the invisible messengers that pass information between ants, scale their effect when more ants are present. They use a mathematical model to show that such a mechanism is indeed plausible. But they don’t know why larger colonies would need higher temperatures to pack their stores. Kronauer ventures that it could simply be that the larger the colony is, the more difficult it is to move, raising the critical temperature for which moves occur.
In future studies, Kronauer and Gal hope to refine their theoretical model of the decision-making process in the ant colony by interfering with more parameters and seeing how the insects react. For example, they can tamper with the level of pheromones in the ant home or create genetically modified ants with different abilities to detect temperature changes. “What we’ve been able to do so far is disrupt the system and measure the output accurately,” says Kronauer. “In the long run, the aim is to reverse engineer the system to infer its inner workings in more and more detail.”
When ant colonies get bigger, new foraging behavior arises
Asaf Gal et al, The emergence of a collective sensory response threshold in ant colonies, Proceedings of the National Academy of Sciences (2022). DOI: 10.1073/pnas.2123076119
Provided by Rockefeller University
Quote: Ant colonies act like neural networks in decision making (2022, July 20) retrieved September 23, 2022 from https://phys.org/news/2022-07-ant-colonies-neural-networks-decisions.html
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