Over short distances, snails are an ideal means of transport for tardigrades, as the two species often share the same habitats. But it is not without risk for some tardigrades.
The most extreme temperatures, radiation, corrosive products, the most powerful impacts, the vacuum of space: not much can overcome the valiant tardigrades. This species, which measures less than a millimeter, is known to be extremophile: almost indestructible, they survive where so many species would not last more than a few minutes.
Biologists have recently discovered that tardigrades have, in addition to everything else, a gait ” outstanding » : they are good at moving. Except that they are nonetheless small, which poses a problem for crossing great distances. But we reassure you, it takes more to overcome tardigrades. Works published in Scientific Reports April 14, 2022 show they have a solution.
To move, some species of tardigrades overlap an agile and fast species: snails. Sure, that seems counterproductive. But when you are barely a millimeter tall, it changes everything to change habitats faster over short distances.
Snails, vehicles for tardigrades
In the introduction to their research paper, the authors recall that, from the point of view of evolution, the ” dispersal ability of animals contributes to their genetic variability and species persistence “. But the mechanisms of migration over short distances remain poorly studied, which the authors therefore wanted to explore. Especially since the latest study on the relationship between tardigrades and snails dates back 55 years, when we know that they coexist in several ecosystems.
The authors therefore set up a laboratory experiment reproducing natural conditions for wood snails (Cepaea nemoralis) and tardigrades Milnesium inceptum, which share habitats in Western Europe. The results” support the hypothesis that snails can transfer active tardigrades over short distances “. Clearly, the tardigrades manage to cling to the snails in order to reach a new destination, because the snails are wet enough – note that the trip is not “on snail’s back”, because it is not to the carapace that the tardigrades cling to but well to the body.
Snail hitchhiking works in tardigrades that are in an active state, as well as in those that are cryptobiosis — a dry state that puts their body on “pause” and allows them to survive extreme conditions.
Tardigrades fortunately adopt other means of transport, and some are more efficient for traveling long distances. As a general rule, they will be able to imprint the rivers or, even more effectively, let themselves be carried by the wind up to 1,000 kilometres. However, these routes can lead to hostile ecosystems, less adapted to the habitats of tardigrades, where the snail route ensures that you end up in a suitable humid ecosystem.
Travel is not without risk for tardigrades
The ride is not without risk, however. Snail mucus is part of the rare tardigrade kryptonite, at least for those who are in a state of cryptobiosis during transport. For them, physical contact with mucus is often fatal: only 34% of tardigrades in cryptobiosis were able to live again after contact, compared to 98% in the control group which was not in contact.
The researchers observe in particular that the mucus, which then coats the body of the tardigrades, dries out too quickly: this disrupts the rehydration cycle which allows the tardigrades to “resurrect” from their state of cryptobiosis. Most tardigrades that do not survive end up frozen due to the dried mucus that coats them.