the ants and The plants have gradually evolved together to cooperate, and since tens of millions of years. This is the conclusion of a new study, published in the scientific journal Proceedings of the National Academy of Sciences (PNAS), which traces the history of this natural complicity. To achieve this, three researchers of the national Museum of natural history Field natural history (Chicago, Usa) have compared the differences in DNA of two groups of organisms : 1 700 species of ants and 10 000 categories of plants. The analyses show that their welfare is much more ancient than anticipated : its beginnings date back to the period of the mesozoic era, that is to say, between 66 and 250 million years before our era !

In this specific case, the cooperation (or symbiosis) takes several forms between the animal and the vegetable. On the one hand, plants have developed a preference for attract, nourish or protect these insects. On the other side, the ants are used to a better dissemination of valuable seeds, and sometimes are in charge of protecting this “hand” that feeds them. “The plants have established several biological structures, used exclusively to ants, explains the lead author of the study, Matthew P. Nelsen. Some, for example, have a nectar attractive to these soldiers with six legs, to the point that they live nearby and attack anything that threatens their source of treasures green.”

As for the egg and the hen, that has started ?

This principle of mutual is found by the entomologists of the world, except that a mystery existed still to science. A riddle, worthy of the paradox of the chicken and egg : which, of the ant or the plant, has started this story common biological ? In search of an answer, the three scientists have gathered huge libraries of DNA from these organisms. They have been recomposed and enriched what looks like the family trees of individuals, but rather in the version of evolution, with entire lineages by branches, over millions of years (technical phylogenetics). According to each family of species, the appearance on Earth varies just as much as the capacity of cooperation to be found. Rearrange these families over time allows to return to the origins of this assistance, and especially to find who has made what.

“The simple idea behind it is to understand the relationships between all species, to highlight events of diversification, while others are extinct,” explains Guillaume Besnard, director of research at the laboratory Evolution and biological diversity (CNRS/university of Toulouse). “Hard to do better than the study in question, with this technique, he adds. The researchers have used a nice exhaustive sample of DNA and databases developed to decrypt it.” And in particular, distinguish each biological capacity dedicated to such cooperation, such a nectar, or a bag nutritious. For the dating on the phylogenetic tree, the minimum ages given by the fossils already known.

The evolution of biological structures dedicated to this cooperation. The ants adapt more quickly than plants.

PNAS / Field Museum of Natural History, Chicago

“In some cases, the nature operates a counter-selection”

Sometimes, a few cases deviate from this grid of reading, with a service rendered involontaireentre species, or non-mutual. Several plant species cunning of all, and by attaching their seeds in a bag (a élaïosome) of a food is popular with the ants, encouraging them to flight, and therefore dispersal of seeds in nature. In other words, natural selection has been hijacked by the appetite of these insects… to his advantage. In the Face of these cases, several u.s. media dare to the metaphor of slavery. Guillaume Besnard refutes this approach. “The ants can cheat, for example by flying a food, however in these cases, the relationship quickly becomes unstable : if the family of plants, there is no interest, it withers and dies. Nature operates in a counter-selection.”

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Between the two families of species, another discovery has surprised the researchers. Their work determines that these insects have relied on this greenery – such as food or habitat – well before the opposite is true ! “Among the ants, who rely a lot on the plants, we’ve even established an order of appearance progressive of their addiction : first, the predators feed on the occasional plant, and then their plan evolves to force [to become an omnivore or herbivore], before finally to make a nest,” commented Matthew P. Nelsen. It took a few tens of million years later for the plants to adapt and thrive eventually of their visitors. Each at its own pace, like in an old married couple.