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The Carletonian

The Carletonian

The Carletonian

Arb Notes: Orange slime engulfs Arb species

<ange substance coating a few feet of grapevine recently attracted the attention of your student naturalists.  It was so brightly orange that it resembled spray paint from a distance, but up close it looked and felt more like a damp mushroom skin full of Jell-o, and, when poked, emitted a clear liquid that tasted and smelled like water.  Had an extraterrestrial invaded the Arb?

This entity would not seem out of place as a science fiction antagonist.  It slowly travels the forest engulfing its prey, including fungi, bacteria and protozoa.  Amazingly, this mass consists of many arguably individual organisms, united into a single cell, which, in related species to this one, may grow to many meters in length. Its lifecycle includes a haploid spore phase, out of which come cells that combine into diploid amoebae.  The amoebae in turn combine to form this super-cell, called a plasmodium, which releases the spores.  This otherworldly organism actually belongs here in our Arb, and it was an acellular, or plasmodial, slime mold.

These acellular slime molds, together with their cellular slime mold cousins that do not fuse when they aggregate, blur the line between unicellularity and multicellularity.  Not surprisingly, slime molds have proven important in the study of evolution, but other fields have made interesting practical use of these organisms as well.  Japanese mathematical biologist Toshiyuki Nakagaki discovered that acellular slime molds can grow to solve a maze in the shortest possible way, given a food inducement at the far end.  His team recently went on to use slime molds to model the best possible routes for the Tokyo train system, as no mathematical model yet can, by turning slime mold loose in a map of stops made of food.  Mitch Resnick and Evelyn Fox Keller at MIT created equations based on the aggregation of cellular slime molds that have since been used to program behavior of characters in video games, and to model the group movement of animals, such as ant colonies.

So, be on the lookout for these bright, fascinating creatures as you explore this week.  Note that the Annual Arboretum Bird Count, an Arboretum Work Event, and a Birding for Beginners Field Trip all occur next weekend; check out the Arb website for more information.  As always, now is a great time to enjoy the Arb!

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