Tardigrades – colloquially known as water bears or moss piglets – are eight-legged segmented micro-animals that are found everywhere on Earth, from mountaintops to deep oceans, and from tropical rainforests to polar regions. Although they are only about 0.5 millimeters-long when fully grown, they are among the most resilient species of animals, being able to survive extreme conditions, such as high temperatures and pressures, dehydration, or even exposures to massive amounts of radiation.
However, since they are so small, they can only travel very short distances by themselves. This made scientists wonder how it is possible that they populate the entire biosphere, exhibiting a genetic diversity of over 1,400 species. A new study led by the Adam Mickiewicz University in Poland has found that these fascinating creatures can travel long distances by clinging to the bodies of larger, more mobile animals, such as snails.
In a laboratory experiment, the scientists placed a number of tardigrades belonging to the species Milnesium inceptum by themselves in a box. In a second box, they put tardigrades together with a species of snail that can be found in their natural habitats (Cepaea nemoralis), while in a third box they put together tardigrades, snails, and moss – a plant species on which tardigrades often reside in nature.
After three days, the researchers checked how many tardigrades remained in the same location and how many of them moved. They discovered that tardigrades only left their original location in the box with snails but no moss. These findings suggests that they might be picked passively by moving snails, a phenomenon that is less likely if they are embedded in moss.
“This emphasizes the role of the fine-scale dispersion of tiny animals,” said study lead co-author Milena Roszkowska, a doctoral student in Bioenergetics at the Adam Mickiewicz University. “Short-distance transportation of invertebrate animals may have a significant impact on their genetic diversity.”
Sadly, the researchers discovered that some of the tardigrades died from contact with the snails’ mucus. However, since these animals reproduce asexually, only one needs to survive the journey in order to establish a population in a new area. Thus, snail travel could still remain a viable and effective way for tardigrades to populate new habitats.
Further research is needed to clarify whether this type of transport occurs in natural environments too, and, if so, how often. In the future, scientists aim to conduct field studies to explore the patterns of movement of these fascinating organisms in the wild.
The study is published in the journal Nature Scientific Reports.