An ant colony has memories that its individual members do not have


Like a brain, an ant colony works without central control. Each is a set of interacting individuals, neurons or ants, using simple chemical interactions that, overall, generate their behavior. People use their brain to remember – but can ant colonies do it too?

This question leads to another question: what is memory? For people, memory is the ability to remember something that has happened in the past. We also ask computers to replicate the actions of the past – the fusion of the idea of ​​the computer as the brain and brain as a computer has led us to take the word "memory" to represent something like the information stored on a hard drive.

We know that our memory depends on changes in how a set of linked neurons stimulate each other; that it is reinforced in one way or another during sleep; and that recent, long-term memory involves different connected neural circuits. But we still do not know much about how these neural events combine, whether we use stored representations to talk about something that has happened in the past, or how we can continue to perform a previously learned task such as reading or reading. ride a bike.

Any living being can present the simplest form of memory, a change due to past events. Look at a tree that has lost a branch, he remembers how it grew around the wound, leaving traces in the bark pattern and the shape of the tree. You may be able to describe the last time you had the flu, or not. Anyway, your body remembers one way or another, because some of your cells now have antibodies, molecular receptors, that correspond to this virus.

Past events can change the behavior of ants and ant colonies. Individual carpenter ants offered a sweet treat to the sugar which is remembered for its location for a few minutes; they were likely to go back to where the food had been. Another species, the ant of the Sahara desert, winds around the arid desert, in search of food. It seems that an ant of this species remembers the distance traveled or the number of marches made since the last time that she was at nest.

A colony of red ants remembers its network of trails leading to the same trees, year after year, although no ant does. In the forests of Europe, they feed on large trees to feed on aphid excretions that feed in turn. Their nests are huge mounds of pine needles located in the same place for decades, occupied by several generations of colonies.

Each ant tends to follow the same path day after day to the same tree. During the long winter, ants snuggle under the snow. Finnish myrmecologist Rainer Rosengren shown when ants emerge in the spring, an older ant goes out with a young one along the usual trail of the older ant. The oldest ant dies and the youngest ant adopts this path as its own, thus causing the colony to remember or reproduce the traces of the previous year.

Search for food in one combine The colony of ants requires an individual memory of ant. Ants look for scattered seeds and do not use pheromone signals; If an ant finds a seed, there is no point in recruiting others because it is unlikely that there are others nearby. Foragers use a trail that can extend up to 20 meters from the nest.

Each ant leaves the path and goes in search of food. He searches until he finds a seed, then returns to the trail, perhaps using the angle of sunlight as a guide, to return to the nest, following the flow of outgoing foragers. Once back in the nest, a loot drops his seeds and is forced to leave the nest at the speed with which he meets the other scorers returning with food. On his next trip, he leaves the trail at about the same place to do a new search.

Each morning, the feeding area of ​​the colony changes shape, like an amoeba that grows and shrinks. No individual ant remembers the current place of the colony in this model. On each hunter's first trip, he tends to go beyond the rest of the other ants traveling in the same direction. The result is indeed a wave that goes further as the day progresses. The wave is slowly fading, as ants coming to sites near the nest seem to be the last to give up.

Day by day, the behavior of the colony changes and what happens one day affects the next day. I pipe a series of disturbance experiments. I put toothpicks that the workers had to move or I blocked the trails so that the foragers worked harder or create discomfort that patrollers tried to repel.

Each experiment directly affected only one group of workers, but the activity of other groups of workers changed, because the workers of a task decided to be active according to their frequency of brief meetings with workers of other tasks. After only a few days of repetition of the experiment, the colonies continued to behave as they had been disturbed even after the end of the disturbances. The ants having changed task and position in the nest, the dating patterns took some time to return to the undisturbed state. No particular ant remembered anything, but in a certain sense the colony remembered it.

The colonies live 20 to 30 years, the life of the single queen who produces all the ants, but each ant lives at most a year. In response to disturbance, the behavior of the oldest and largest colonies is more stable than that of the youngest colonies. It is also more homeostatic: the greater the magnitude of the disturbance, the older the colonies were likely to focus on foraging rather than the hassle response I had. established; while, the more the situation deteriorated, the younger the settlements reacted. In short, the oldest and largest colonies grow to act with greater wisdom than the smaller ones, even though the oldest colony does not have older and wiser ants.

Ants use the speed at which they meet and feel the other ants, or the chemicals deposited by other ants, to decide what to do next. A neuron uses the speed at which it is stimulated by other neurons to decide whether to trigger or not. In both cases, memory results from changes in how ants or neurons connect and stimulate each other. Colony behavior is likely to change as colony size changes the rates of interaction between ants.

In an older and larger colony, each ant has more ants to meet than in a younger, smaller colony, and the result is a more stable dynamic. Perhaps the settlements remember a past disruption because it moved the location of the ants, which resulted in new modes of interaction, which could even reinforce the new behavior overnight, while the colony is inactive, just as our own memories consolidate during sleep.

Changes in colony behavior due to past events are not just the sum of ant memories, just as the changes in what we remember and what we say or do, are not a simple set of transformations, neuron by neuron. Instead, your memories resemble those of an ant colony: no particular neuron remembers anything, unlike your brain.

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