April 11 () –
Scientists have identified the unique mechanism used by termites to mass-build their meter-high nests, with complex communication and ventilation structures inside.
To carry out their laboratory experiment with termites of the species Coptotermes gestroi (native to South Asia, but which has spread to the east coast of the United States), researchers led by the IMT School for Advanced Studies Lucca (Italy) They created small arenas with artificial structures of different heights and shapes using wet clay.
They then collected small populations of termites from a larger colony and quantified their building behavior in response to these structures by video-tracking the activity of all termites in the population, while characterizing changes in 3D structure. Thus, It was possible to test several hypotheses to discover the coordination mechanism used for nest construction.
In the case of ants, which along with termites are the other large group of insects capable of building, for example, large and intricate structures, it is believed that they impregnate the construction material with a pheromone, a chemical substance that attracts others. ants to the construction site and “tells” them where to build. In this way, the action of a worker ant triggers the activity of other ants in a self-amplifying process.
If termites, like ants, also depended on pheromones to guide their construction activity, then they should not show a preference for depositing their pellets of construction material in any particular location, because there were no pheromones in the artificial sands prepared by the experimenters. But this was not the case: while the collections of material occurred throughout the sand, the depositions were all located on top of the already existing structures.
Perhaps they could evaluate the elevation of small pillars and the heterogeneities of the terrain, and in this way they would continue adding construction material on top of the already existing structures. But that was not the case either: in fact, the termites deposited their construction pellets with the same probability on both low pillars and high pillars.
Another hypothesis was that termites could sense the curvature of the building's substrate, since some previous models had shown that constantly adding beads in places of greatest curvature is enough to produce very complex structures that resemble the termite nests of some species. .
“In our simulations, we observe that small surface heterogeneities have a greater curvature than the surrounding flat substrate and therefore expand to form a pillar; the pointed ends of the pillars, in turn, attract more deposits of building material and continue to grow until they split or merge with another pillar, etc.; Very complex structures can be formed with this simple rule” says Giulio Facchini, first author of the study and researcher at the CNRS Institut Matière et Systèmes Complexes in Paris, France.
In fact, when the termites were faced with the artificial stimuli provided in the experiments, They always preferred to build in places with the greatest curvatureadding beads to the top of the pillars (regardless of their height), and when a small stimulus from the wall As planned, most of the time they continued adding beads to the two corners of the wall, the two points where the curvature reaches its maximum.
The problem is: how could termites so reliably detect the curvature of the structures they were building? The researchers had a clue that water evaporation and humidity might have something to do with it.
“Termites are very sensitive to humidity concentrations: unlike most other insects, they have a thin exoskeleton and soft skin, meaning that even prolonged exposure to humidity levels below 70% can be lethal. for them,” explains Andrea Perna, professor of complex systems at IMT and research coordinator. ““It's not surprising that they can sense these humidity gradients and respond to them with their behavior.”
“We found a solution that one of eLife magazine's anonymous reviewers described as 'very clever and low-tech': We prepared experimental sands identical to those used with termites, but this time impregnating the clay with a saline solution. of baking soda,” explains Facchini.
“As the water in the saline solution evaporated, it left small salt crystals, the growth of which marked the regions of greatest evaporation: these were the tips of the pillars, the corners of the walls: exactly the same regions that the termites had selected for their construction activity.
“What really surprised us was discovering that termites use such a simple solution to a very complex problem,” says Perna.
“In our experiments, the complexity of the nest arises from a single simple mechanism: the termites only need to add pellets of material depending on the local humidity, but the pellets they add in turn change the entire pattern of evaporation and humidity, inducing other termites to build in a different location, and so on, until very complex structures are produced“he concluded.
