Ant colonies, real and virtual

Formica fusca

Ants, hymenoptera related to wasps, are social insects. An anthill or ant colony can contain, from a few dozen individuals, to over half a million. The number of castes varies, depending on the species, between three (fertile males and females, sterile female workers) and over twenty. The feeding a larva receives decides the caste to which it will belong.

Strange forms of parasitism have arisen among ants, as in Amazons ants (Polyergus), whose workers specialize in fighting and starve in the presence of food, unless a worker of Formica fusca feeds them. To seize these auxiliaries, the Amazons attack the nests of Formica fusca, kill their queen and enslave the workers. In extreme cases, such as ants of the Anergates genus, the queen invades a nest of Tetramorium, supplants its queen, and fed by the workers of the other species, produces eggs that become queens and males, but no workers, which are not needed.

Evolution in social insects probably reached the highest levels of instinctive complexity that can be achieved with a nervous system as limited as that of arthropods. In the tens of million years since the origin of these societies, evolution has introduced secondary changes, which have led to great diversity: there are more than three thousand species of ants, but there seems to have been no progress in their social structure. They are highly successful animals, very abundant, and spread throughout the world, but stagnant.

Ant trail

An ant colony behaves almost like an individual, acts like a higher order organism. Each member can only live in contact with the others. If an ant is lost, it dies in a short time. If it finds another anthill, even of the same species, it won’t be able to join it, as its smell will prevent its being accepted.

In an artificial life experiment carried out by me and Juan de Lara, we analyzed how evolution acts at two levels simultaneously. The organisms we work with resemble ants and ant colonies, but they are not identical. We call them vants (virtual ants)

Vants live together in a virtual anthill (vanthill) and exhibit quite complex behavior. At birth, they are assigned an expected life span, which can change depending on their activity. Initially there is a single vanthill, located in a two-dimensional territory through which the vants can move. A number of food sources are scattered in that territory, which vants can consume and accumulate. The life cycle of a vant can be summarized as follows:

1. It leaves the vanthill and searches for food, moving randomly through the territory. If it cannot find it, it abandons the search, returns to the vanthill by the shortest path and rests. Then it comes out again.
2. If it finds food, it takes a part to the vanthill by the shortest path. Upon arrival, it consumes part of the food it has brought (increasing the expected duration of its life) and leaves the rest in the vanthill. If at this time there is at least one other vant in the vanthill and it contains enough food, both can reproduce. The daughter vants inherit the genes of their parents, except for the action of two genetic operators: mutation (random change of some gene) and recombination (shuffling of the genes of both parents).
3. After resting in the vanthill, the vant leaves and returns by the shortest path to the place where it found food the last time. If there is still food there, step 2 is repeated. Otherwise, the vant searches, as in step 1. When a source runs out of food, it disappears, but a new one immediately appears in a random position.
4. When a vant that knows where there is food, either because it has found it, or because it is getting back to the vanthill with a load, meets another vant of the same vanthill that does not know where there is food, it can act in several ways: a) It may refuse to tell where there is food. b) It can tell where food can be found, but in doing so it can tell the truth or deceive in various ways. In turn, the vant that receives information may or may not believe it. This behavior is controlled by their genes.
5. When the number of vants in a vanthill exceeds a limit and there is enough food, half of the vants migrate and build another vanthill. When two vants of different vanthills meet, they can act in these ways: a) ignoring each other; b) the strongest can take food from the other; c) The strongest can kill the other and use it as food.
6. When a vant reaches the limit of its life span, it dies. When the number of vants in a vanthill is less than a threshold, the vanthill disappears.

The vants of a vanthill compete for food on two levels: first, against those of other vanthills, because the available quantity is limited and must be distributed. Secondly, against those of their vanthill, as the one that gets more food will lengthen the duration of its life and will have more opportunities to reproduce.

The attached figure shows an instant during one of the executions of this artificial life program. Letter a represents vants who don't know where the food is and are searching. Letter k corresponds to vants who know where the food is and are going there. Letter b represents vants that return with food to their vanthill. Letter A represents the vanthill. Note that vants that know where the food is, and those that come back, form trails, like real ants.

The results of this simulation are surprising. As long as there is only one vanthill, the genetic trait that prompts vants to lie, when they should tell the position of the food, is positively selected. It is obvious why: a lying vant keeps for itself the position where it found food, so it’s more likely that it will find it again the next time it visits the place. If it tells its comrades where it is, they’ll share it, and it will be exhausted sooner, so when it returns it may not find it. Here selection favors selfish behavior.

On the other hand, when several vanthills compete with each other, selection favors altruistic behavior: vants whose genes drive them to tell the truth proliferate. It also seems evident why: if a vant of a vanthill insists on behaving selfishly, it will lengthen its own life, but at the cost of that of its comrades, and when their number falls below the threshold, the vanthill will disappear.

We see, therefore, that natural selection favors selfish behavior of beings of the lower level as long as there are not several individuals of the higher level, but otherwise it favors altruistic behavior. In these experiments we have started from the previous existence of both levels, that of the individual vant and that of the vanthill. A pending problem is how the upper level can appear in an environment where only lower level individuals exist.

The same post in Spanish
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Manuel Alfonseca