Sunday, November 9, 2008 - 03:36
It was a wet and rainy day yesterday, and we have a dissecting microscope, so I decided to see if I could find some tardigrades.
Tardigrade photo by nebarnixReposted from Nov. 2006 I went outside and scraped a bit of moss and some lichens off of our deck. Then I put the lichens and moss in a dish. We don't have distilled water in our house, so I added a bit of cool some tap water to the dish. I squeezed the moss and lichens in the water. Then I took a pipette and transferred a bit of the stuff in the water to a plastic petri dish and looked for tardigrades. Sure enough, I saw one climbing onto a raft of debris. The creature looked quite a bit like a transparent caterpillar. It wasn't long before the other members of our household walked by and got interested. "What are you looking at?" "I want to see!" I had to give up the microscope so everyone else could check out the tardigrades, protozoans, rotifers, and other mysterious creatures zipping around in the dish. Which, of course, was part of my motive all along. All about Tardigrades Tardigrades are also known as "water bears." They're small, about 0.05-1.2 mm in length, and really cute. About 930 species belong to the Tardigrade phylum. This group of very small animals fits on the evolutionary scale between arthropods and nematodes. They look a bit similar to arthropods because they have eight legs. Tardigrades also have an amazing ability to withstand drying out. They live in water, but if the water dries up, they go into an inactive state, and they can remain in that state, dried up, for years, until it gets wet and they're rehydrated. William Miller explains more about this incredible property:
When the environment dehydrates in dry weather tardigrades desiccate into a reversible state of metabolic suspension called cryptobiosis. They shrivel to about one-third their former size into a wrinkled "tun." Individuals have been observed to come and go from the cryptobiotic state repeatedly and tardigrades have been reported to survive more than 100 years (Kinchin 1994). Cryptobiosis is of great interest in the study of cryogenics and tardigrades have been subjected to laboratory experiments which verified their ability to survive. Tardigrades have tolerated temperatures below freezing at 0.05K (-272.95 C) for 20 hours and -200 C for 20 months. They have survived 120 C, pressures of 1000 atmospheres, and high vacuums. In the cryptobiotic state, tardigrades have shown resistance to hydrogen sulfide, carbon dioxide, ultraviolet light, and X-rays (Kinchin 1994). We could speculate that tardigrades could be transported through outer space in their existing form.Doing science with Tardigrades Part of the reason that I got interested in Tardigrades was because I found this interesting site from the Pathfinder Science Network. Opportunities for students to design and carry out their own experiments are kind of a holy grail for many science teachers. This virtual community has developed several experiments to meet that need. Their goal is to give students a chance to do science and not just repeat procedures. Pathfinder experiments cover a diverse set of topics ranging from global warming to the migration of humans, monarchs, and birds. Some students have even published their work on the Pathfinder site. I can imagine all kinds of fun experiments that you can do with tardigrades. They have many great advantages. They're cheap, found just about anywhere (there are even tardigrades in the Antarctic!), and kind of cute. Plus, a great advantage (from my standpoint) is that there are a some Tardigrade DNA sequences in the database, so we can even do a bit of molecular phylogeny. In the meantime, I've compiled a list of resources to help you get started. Tardigrade web sites and references 1. William Miller, "Tardigrades: Bears of the Moss (About Tardigrades)" at the PathFinder Science Network. 2. The Tardigrade Newsletter banner Background information, recent papers, news, people who study tardigrades. They have some great electron micrographs of tardigrades and their eggs that you can download and use as wallpaper on your computer. 3. www.tardigrades.com This site has images, video clips and a monthly magazine. 4. Taridigra in the Tree of Life Web Project. There are some nice drawings of tardigrades here, more links, and a long list of papers 5. Molecular resources about Tardigrada from the NCBI. 6. There is a a great movie at the Pathfinders site that's very helpful in getting started. The movie shows how to find tardigrades, how to transfer them to a slide, and some of the features you can see when you've got tardigrades swimming around in a dish. The PowerPoint presentation crashed my computer, so you might want to avoid that one.