Both the photographs and write-up are courtesy of Bryant today:
Today’s image is of Lycogala epidendrum, also known as wolf’s milk slime. It is a slime mould in the Reticulariaceae and the class Myxogastria. The Myxogastria is a fascinating grouping of slime moulds (or myxomycetes) that contains a recognized 60 or so genera and about 900 species. Lycogala epidendrum is cosmopolitan in distribution, like many other slime moulds. Also common to slime moulds, Lycogala epidendrum goes through a number of rather incredible morphological phases as it matures. Myxomycetes are perplexing organisms that demonstrate characteristics associated with both animals and fungi. Here are some of the highlights of their strange life cycle:
Members of the Myxogastria begin their life cycle after spores germinate. Haploid myxamoebae or myxaflagelletes are produced. Myxamoebae (crawling unicellular organisms) are produced if conditions are dryer and myxaflagelletes (swimming unicellular organisms) are produced if conditions are considerably moist. These unicellular organisms, also known as swarm cells, move around on a substrate such as this rotting log as the devour bacteria/fungal spores/dissolved substances. As the unicellular forms gorge themselves, they can asexually reproduce through cell division. Depending on environmental conditions, two paths of development are followed. If there is a drastic change to undesirable conditions, these unicellular forms may begin a resting phase, morphing into thin-shelled forms known as microcysts. Microcysts can survive for periods of up to a year or more, until conditions change for the better. As conditions improve, they will become active monocellular amoeba-like forms once again!
If conditions stay suitable, these unicellular organisms will start to mate once they encounter the correct mating type. The result is the fusion of protoplasm/nuclei into diploid zygotes, which develop multiple nuclei through nuclear division (not cell division). These multinucleated monocellular organisms are known as plasmodium, which can be seen with the naked eye. The plasmodium continues to grow as it gains nourishment through phagocytosis. Plasmodium can grow into mats of protoplasmic strands up to a meter in diameter or more depending on the species. The plasmodium is also mobile and has the ability to move towards useful chemicals/food (chemotaxis) as well as towards/away from light (phototaxis). As if that wasn’t astonishing enough, the movement is caused by the cycling of protoplasm within the protoplasmic strand, and it can move at speeds up to 1.35 mm/s, one of the fastest speeds recorded for any micro-organism! For comparison, some of the highest velocities recorded in plant cells reach a peak of about .078 mm/s. To see some slime moulds in action, check out these videos of slime moulds doing amazing things: Slime Moulds Time Lapse, Comatricha sp., Slime Mould Solves Maze, and Slime Mould Forms a Map of the Tokyo-area Railway System.
Finally, once food supplies have been diminished or other environmental factors change for the worse, the plasmodium may either transform into rigid structures known as macrocysts that will enable it to survive the adverse conditions until they improve. Often, this means over-wintering. Alternatively, the plasmodium may form into fruiting bodies, as pictured above. At this point, the plasmodium ceases phagocytosis and moves towards a dryer/ brighter area via positive phototaxis. Doing so enables better dispersion for its spores once the fruiting bodies have matured and dried out.
John Tyler Bonner (one of the world’s leading experts on Myxomycetes) sums it all up rather simply, “[Myxomycetes are] no more than a bag of amoebae encased in a thin slime sheath, yet they manage to have various behaviours that are equal to those of animals who possess muscles and nerves with ganglia–that is, simple brains”.