When temperatures are rising, ant colonies need to make collective decisions. While each ant feels the heat rising beneath its feet, they carry along as usual, until they suddenly reverse course, with the whole group evacuating their nest. A team of researchers from the Rockefeller University has found that, in such situations, ants as a group behave similar to networks of neurons in the brain.
By developing a new experimental setup to rigorously analyze decision-making in ant colonies, the researchers discovered that when a colony evacuates its nest due to rising temperatures, its decision is a function of both the magnitude of the heat increase and the size of the colony. Thus, ants combine sensory information with the parameters of their group in order to arrive at a collective response – a process similar to how neural networks in the brain give rise to decisions.
“We pioneered an approach to understand the ant colony as a cognitive-like system that perceives inputs and then translates them into behavioral outputs,” said study senior author Daniel Kronauer, an expert in Social Evolution and Behavior at Rockefeller. “This is one of the first steps toward really understanding how insect societies engage in collective computation.”
Decision-making consists of a series of computations meant to minimize costs and maximize benefits. For example, in a type of decision-making called sensory response thresholding, an animal has to detect sensory input such as heat exceeding a certain level to produce a costly behavior, like moving away.
The scientists exposed ant colonies of 36 workers and 18 larvae to rising temperatures, and found that, when the temperature exceeded 34 degrees Celsius, the ants evacuated their nest. Surprisingly though, if the size of the colony was larger – about 200 individuals – the ants only evacuated the nest when temperatures rose to 36. “It seems that the threshold isn’t fixed. Rather, it’s an emergent property that changes depending on the group size,” said Professor Kronauer.
According to the scientists, pheromones – the invisible chemical messengers that pass information among ants – play a crucial role in structuring this collective behavior. It is not yet clear though why larger colonies would require higher temperatures to pack up shop. A hypothesis is that the larger the colony size, the more onerous it is to relocate.
In future studies, the researchers aim to refine their theoretical model by interfering with more parameters – such as tempering the level of pheromones in the ants’ enclosures or creating genetically altered ants with different abilities to detect temperature changes – and observing how the insects respond.
“What we’ve been able to do so far is to perturb the system and measure the output precisely. In the long term, the idea is to reverse engineer the system to deduce its inner workings in more and more detail,” Kronauer concluded.
The study is published in the journal Proceedings of the National Academy of Sciences.