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These ambling, eight-legged microscopic “bears of the moss” are cute, ubiquitous, all but indestructible and a model organism for education

William R. Miller

Getting Around

2011-09MillerF6.jpgClick to Enlarge ImageTardigrades have been discovered just about everywhere that anyone has looked, from the Arctic to the equator, from intertidal zones to the deep ocean, and even at the top of forest canopies. Their ubiquity is intimately linked to their survivorship. I am often asked how tardigrades manage to find their way to the canopy of towering trees. Most likely, wind carries them. In the tun state they are barely distinguishable from dust particles. But like spores, pollen and seeds, the tuns have a preference for where they land. Many microenvironments will be unsuitable habitats for freshly arrived tardigrades. Yet an unhappily placed tun can simply wait for a change in precipitation or perhaps a change in season. When conditions improve, life can begin again.

Contributing to their success as travelers is the fact that many tardigrades of moss, lichen and leaf litter are parthenogenetic, able to produce eggs without mating, and in a few cases are hermaphroditic, able to self-fertilize. A lone tardigrade on an ill wind—active, tun or egg—may be able to establish a population where it lands if the habitat is suitable. We may be under tardigrade rain right now.

2011-09MillerF7.jpgClick to Enlarge ImageAt present there are about 1,100 described species of water bears, but not all are valid. Some descriptions are repeats and some are just plain flawed. Around 1,000 species have been properly identified and described. We have about 300 marine, 100 freshwater and 600 terrestrial species. But the land species are much easier to find and have been pursued by many more researchers over many more years. Still, my students have discovered and described four new species so far, and we are working to confirm another half dozen, including one found on the campus of Baker University in Kansas, where I am a faculty member. We believe there is an abundance of species yet to be discovered, especially in the nonterrestrial environments.

I might discover a new species? she asks.
Yes, sitting at a microscope, you might observe an animal nobody in the world has ever seen before. That is pure exploration. In the blink of an eye, you might find a clue to the evolution of the phylum or identify the animal that holds the cure for cancer, I say. Then again, you might not. It took me 16 years to find my first new species.

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