Tardigrades can hitchhike on snails to travel longer distances

Although incredibly resistant, tardigrades are also too small to travel very far – unless they are riding a larger animal.


April 14, 2022

A tardigrade seen with a scanning electron microscope


Tardigrades can hitchhike on passing snails to travel relatively long distances, according to laboratory studies.

Sometimes called water bears, tardigrades can survive extreme environments in a dehydrated state called a tuna. But because they are so small, they can only walk a short distance themselves. However, this creates a mystery, as tardigrades are found all over the world, with a genetic diversity of more than 1400 species.

Many small animals can travel long distances by clinging to the body of a larger, more mobile creature. This behavior has never been observed in tardigrades, so Milena Roszkowska and Zofia Książkiewicz at Adam Mickiewicz University in Poland decided to investigate.

The couple used lab studies to test whether snails can transport tardigrades. In a box, they placed a number of tardigrades belonging to the species The Millennium Initiative by themselves. In a second container were tardigrades plus a species of snail (Onion) which occur in their natural habitat, while in a third box there were tardigrades, snails and mosses, where tardigrades often reside in nature.

After three days, the researchers counted how many tardigrades remained in their original place and how many had moved, and whether they were alive or dead. They found that living tardigrades only left their starting point in the boxes where snails were found without moss. They speculate that this may be due to tardigrades being picked up passively by passing snails, and that this process is more unlikely if the tardigrades are embedded in moss.

“This emphasizes the role of small-scale dispersal of small animals,” says Roszkowska. “Short-distance transport of invertebrates can have a significant impact on their genetic diversity.”

The researchers found that the tardigrades in moss did not travel more than the control group, which indicates that the effect only occurs in certain natural scenarios.

They also found that some of the tardigrades died from contact with the snail’s mucus. But the ability of tardigrades to reproduce asexually means that only one needs to survive the journey to establish a population in a new area. This means that snail travel can still be a sustainable way for tardigrades to populate new habitats.

Although the study shows that snail-based transport is possible for certain tardigrades, researchers still do not know if the tardigrades are transported in this way in nature – or how often. One variable is that the humid habitats tardigrades and snails need to survive can change over time. – It depends on the weather conditions. During wet years, tardigrades can be transmitted by snails more often than during dry years, says Książkiewicz.

“The fact that it has potential makes it interesting,” said Sandra McInnes of the British Antarctic Survey. “It’s something someone has not done before. This experiment is a pilot study to see if it is feasible and they have proven it to be.”

Future experiments, says McInnes, should now try to observe that this happens in natural habitats.

Journal reference: Scientific reportsDOI: 10.1038 / s41598-022-08265-2

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