We have had a wonderful series of rains along the Colorado Front Range, and many moisture-sensitive organisms are showing up. The picture shows one of the less photogenic of the slime molds, probably from genus Fuligo. I was surprised to see this one preparing to form its spores in the thin duff under a juniper tree. The first time I saw it, it was a spongy, cream-colored mass. That day I hadn’t brought my camera – a lesson for me to be more prepared this time of year. I went back the next day and took this photo. The mass had shrunk and liquid pools appeared on its surface as it converted to spores.
Slime molds are incredible creatures that spend part of their life cycle as individual cells and part as a multicellular or multi-nucleate structure. They have a more attractive name – the social amoebas, but more information is listed under “slime mold.” The basic life cycle of social amoebas involves spores that germinate into individual cells. These amoebas eat bacteria from decaying plant materials. When food runs low, the cells send out a chemical signal that calls all of their kind to come together and make spores. The spore-bearing structures can be elaborate and beautiful, but they are small and easily overlooked. If you want to see a variety of them, go to this listing, http://www.uoguelph.ca/~gbarron/myxoinde.htm. For a story about hunting slime molds in the Great Smoky Mountains National Park, see this article from Smithsonian Magazine: http://www.smithsonianmag.com/science-nature/phenom_mar01.html. The Discover Life website has good information and photos as well: http://www.discoverlife.org/20/q?search=Eumycetozoa.
It is easy to bring a slime mold into the classroom. To make its home, you need an empty Petri dish or similar container, some paper towel, and few flakes of old-fashion oatmeal. Scientific supply companies sell the dried form of the organism, Physarum polycephalum. It is a resting structure called a sclerotium. If a slime mold in its active state dries out, it can form a sclerotium and hunker until the moisture returns. To grow the slime mold, cover the bottom of the Petri dish with clean, white paper towel, sprinkle in about a half-dozen flakes of rolled oats, and moisten this well, but don’t add so much water that there are puddles. Place the sclerotium in the dish. Don’t worry if it looks like lots of orange flakes – the parts will find each other and come together. Place your culture in a re-sealable plastic bag to retain moisture and to keep the slime mold from migrating out. Put the whole thing in the dark to prevent the organism from forming spores. The yellow slime mold will become active and move around the Petri dish. When you are finished observing the slime mold, you can put it in the light and use a magnifier to look for the spore-bearing bodies – small black structures that give it its name, the many-headed slime. To see photos of this slime mold in several stages, see the first link above. Here’s a link to more culture information: http://www.educationalassistance.org/Physarum/EasyToGrow/PHYSARUM%20culture%20for%20web.html.
Slime molds are members of the unikont branch of eukaryotes and the amoebozoa branch of unikonts. They make up the mycetozoa branch of amoebozoa. The term “myxomycetes” is used for the acellular slime molds, those whose amoebas fuse together into one big mass. Older classifications placed the slime molds in the fungus kingdom, to which they are only distantly related.
If you want to stalk the wily slime mold, a magnifier is a great help. Wet weather, decaying vegetation, and patience are also needed. Happy hunting!