How the snail “Partula hyalina” avoided extinction … and how the smallest computer in the world knew how to determine it

CIt could be the story of a massacre, one of the many ecological catastrophes caused by the all-powerful human species. This has, moreover, led to the disappearance of 56 species of land snails native to Tahiti and Moorea, in the Windward Islands, in the heart of the Society archipelago. The article published in Communications Biology however tells the other facet of this drama: it indeed solves the mystery on the way in which Partula hyalina managed to escape the carnage. An investigation conducted by an American team thanks to “Smallest stand-alone computer in the world”, say scientists.

The story begins in the 1960s. In French Polynesia, breeders have the idea of ​​importing giant African snails. But what we take for a simple food resource quickly turns into a plague for crops. Never mind, agronomists find the solution: Euglandina rosea. The Anglo-Saxons gave this other species of shelled gastropod the sweet name of pink wolf snail, which gives an idea of ​​its color … and its appetite.

Introduced in 1974, the carnivore will attack all its cousins. Of the 61 species in the archipelago, only 5 will resist the predator. In the family Partulidae, a florilège of diversity that earned him the nickname “Darwin’s finches of the world of snails”, only the white shell of P. hyalina and, to a lesser extent, that a little darker of its first cousin P. clear escape the slaughter.

Reflective shell

Professor of ecology at the University of Michigan, Diarmaid O Foighil hypothesized, in 2015, that this light coloration could play a role in the resistance of the gastropod. Her student Cindy Bick first highlights the highest reproductive rate of P. hyalina. But it also establishes that this physiological data alone is not sufficient to explain this survival. She is embarking on a thesis devoted to what she will call a “solar refuge”.

The color of the shell would allow it to reflect the light rays rather than absorb them, and thus to support the sun of the edges of forests, its preferred habitat, she supposes. Drying out is, in fact, the greatest danger for snails, which come out at night but flee the daytime sun.

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But how to prove this theory? The luck of the two biologists resides a few buildings from their office. Computer engineer David Blaauw developed the M3 there, presented in 2014 as the most compact computer in the world. A few millimeters large, autonomous and modular, the device is adapted to incorporate a light sensor. Researchers make about sixty of them. Some are stuck on the shells of pink predators. But no question of touching the integrity of P. hyalina, protected species in Polynesia. It is therefore by magnetizing the M3 on either side of the leaves where the gastropods are housed that the scientists will collect the data.

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