Strangest Creature on Earth

Not a fungus, plant or animal but behaving intelligently

I learned about these strangest of all organisms already at high school from my teacher Dr W. Ruppolt. And how long ago that was, you can guess from the following comment. At that time slime moulds were seen as organisms straddling the boundary between plant and animal life. They were placed into a separate category of fungi and in those days fungi were considered plants without chlorophyll. It’s all changed: fungi are now regarded as a phylum separate from plants and animals. The slime moulds are neither fungi nor plants and whether one can call them ‘animals’ is also more than doubtful. So, like other unclassifiable organisms they are now called “Protists”. They have, however, amazingly interesting characteristics and this is why they have attracted so much attention in recent years.

There are basically two somewhat similar but evolutionarilly most likely unrelated types. Some, like Dictyostelia spp., start their life as single cell amoeba that crawl around on rotting logs, enter crevices, multiply by fission and feast on bacteria and other minute foodstuffs. If food becomes scarce the amoebae produce signal chemicals which “call together” the individual amoebae from all the nooks and crannies they are hiding in to form what is appropriately termed “a slug”. These whitish usually no more than 10 mm long “slugs” crawl along to find an open, elevated and lit place, where they create a stalked “fruiting body”. Some amoebae sacrifice themselves, die and become the hardened vertical stalk, while others transform into spore-producing individuals at the tip of the stalk, i.e. the fruiting body. The spores are distributed by the wind, then turn into amoeba and the cycle can begin anew.

The other group of slime moulds contains the plasmodium-forming Physarum polycephalum (from physa = pustule and polycephalum = multiheaded). Chances are you’ve seen the species on rotting logs as branched, sometimes spiderweb-like yellow strings, but did not pay much attention to this feature of Nature. Perhaps you should have, because what you see best in autumn is the plasmodium of the organism. A plasmodium can be described as single gigantic cell with multiple nuclei, but no cell walls or membranes present. Plasmodia move around by “streaming”, which is a process in which an inner less viscous sol-like substance is surrounded by the somewhat tougher outer gel-like material, containing actin filaments. Streaming involves rhythmic and erratically changing movements of the plasmodium and a speed of 1 mm per second can be reached. The size covered by a plasmodium fully spread out may be as extensive as a metre (but usually is much smaller). During this plasmodial phase the single cell, but multinucleate “super organism”, engulfs small edible particles and bacteria and avoids bright light, especially blue and UV. The organism has a keen chemical sense and is guided unerringly to a food source (it loves oats and sugary substances, but avoids salt and caffeine).

Why this organism has received such a lot of attention is its ability to move around, to solve problems, to learn and to memorize things  –  all without a brain and differentiated tissues! This organism has led scientists to re-define “intelligence” and its ability to find the shortest escape route in a maze or to connect different food deposits in the most effective way has intrigued researchers no end. In order to sporulate, the plasmodium re-organizes itself to form an often quite colourful fruiting body, from which spores are released. Some of the spores are amoeboid and can crawl along while others are flagellate (possessing flagella). The two kinds of spores are apparently interconvertable. I guess by now you will have become so attached to these “slimeblobs” that you may wish to own one as a pet. If that’s the case get some advice from here.

© Dr V.B. Meyer-Rochow and, 2020.
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