West Cork Palaeoecology - Blog
The Environment of West Cork through Time
- +353 (0)83 0744708
As with so many things in nature, the indigenous or common name is based on appearance. And so it is with this slime mould. (It is also called 'scrambled egg slime mould').
IMPORTANT UPDATE. The blog below entitled 'More on Slime Moulds' refers and corrects this blog.
Dog vomit slime mould (Fuligo septica) on moss in a larch plantation in West Cork, July 2023
Despite the common name, and the general name of 'slime mould', this is a fascinating organism that is well worth applying some consideration to.
The slime mould pictured here is just one process in a chain, or cycle, of events that leads to propagation of the species. The organism starts off as separate cells, single cells, living in an amoeba form in their environment. In the case of Fuligo septica the environment is one of rotten wood, or moss, or leaf mould on a woodland floor; or a damp rotting piece of wood. At a certain time, when conditions become either stressful for survival or conducive to propagation - researchers seem divided on what prompts the change - the amoebae, all those individual cells living individual lives - move in a certain direction and start congregating. How these single celled organisms know where to go, and when, is not known by us. But they congregate and form a body of living cells called a 'slug'. Which apparently is similar in appearance to a slug, but without the things slugs have. As a slug, some of the amoeba-like cells act as foragers, some as protectors, and the whole body behaves more like a bee or wasp or ant colony, each individual helping and supporting others. Somehow.
As the process progresses the slug, at an appropriate time, starts to separate into different functional forms. Some form spore producing amoebae, some stem amoebae, and also basal amoebae. And probably other functional types as well. The long and the short of it is that the amoebae that give themselves up to becoming spore producing bodies, are elevated up onto the ends of those that become stems. And after an appropriate time, or at an appropriate time, the spore bodies burst and the spores are distributed out into the environment, where each one will eventually become an individual amoeba.
A closer view of Fuligo septica, Dog Vomit plasmodial slime mould.
In the case of Fuligo, which is a plasmodial slime mould, the individual amoebae, once they have consumed all the bacteria within reach, during which time the amoebae grow and divide and increase in number, they start to coalesce into one large cell incorporating all the nuclei. Eventually, each one of these nuclei will form a spore body and be released.
Starting with the individual amoebae at lower left, we follow the cycle clockwise. Following increase in numbers, fusion of cytoplasm (6 - plasmogamy) and of nuclei (7 - karyogamy), the plasmodium forms by accumulation of the many individuals, and under the right conditions, sporangia form (1), finally releasing spores into the environment (bottom right - 3).
To see the original caption to this diagram, click here.
How do these widely scattered, independently living amobae communicate so that they come together at a single place? Smell? Chemical signals? Sixth sense? They are single cells, they don't have noses, vocal chords, or brains. As is so often the case while studying microscopic organisms, one is left wondering how on earth such small things can communicate, change function, work together, and even appear to make decisions. All in a microscopic world of single celled organisms that we so poorly understand.
It would appear to possibly be something called quorum sensing, which is a bit like pheromones being released into the environment by each individual, and other indviduals sensing thise chemicals. Molecules. But quorum sensing is a bit more complex than pheromones, and is only now being accepted and investigated. For a start the process involves evolved systems of specific signals, with a linked recognition of chemicals upon which to act, so both the sending and receiving of such messages is a specific evolved system. Additionally the concentration of the signal indicates the need to act; so for example if enough amoebae produce the signal, concentration levels in the environment reach a point where the indiduals all start acting, as one. And presumably the signal is also directional, enabling the amoebae can congregate.
It is early days for exploration of quorum sensing, so more will be revealed in time. But just keep hold of the idea that this is something that the (supposedly) simplest of organisms, single celled bacteria, protists, and even viruses, engage in. For us to detect a smell we need to employ our multicellular noses, nervous systems, and brain...
Spore bodies, on stalks, of Fuligo septica - a collage (x100 magnification).
Back to the Dog Vomit. As the sample I took dried out - and presumably came under stress, or entered a state conducive to sporulating - spore bodies formed, small spherical translucent balls on the ends of long, fine stalks.
A spore body of Fuligo septica (x100 magnification).
In this image (a series of photos a different focal points that have been stacked to make a composite image with greater depth than we can actually see through a microscope) we can see some (out of focus) yellow plasmodium, and also some that has darkened as it dries out, and connecting the two, the slime that gives slime mould it's name. The plasmodia are not usually all together in one lump, but are usually more or less scattered, but linked by the slime.
Fuligo septica ripening prior to releasing spores (x40 magnification).
The dried out brown parts eventually split open to release the spores with which they are filled.
A spore body of Fuligo septica ready to split open and release the spores packed inside (x40 magnification).
At the same time, despite overnight rain, the patch in the woods degenerated into a less colourful, less easily seen, mess. And two further patches appeared nearby. We can visualise thousands of microscopic amoebae sliding together across the woodland floor, in response to molecular signals released by them all, coming together and congregating, combining cytoplasm and forming large plasmodium of free flowing cytoplasm containing many thousands of nuclei, all in the silence and darkness on the moss of the woodland floor.
The new patch of Fuligo septica plasmodial slime mould.
As the days passed, with wet nights, cooler weather, wet days, and then back into warmer and drier days and nights - all in mid to late July - different patches of Fuligo septica appeared. Within a day, or at most two, they melted away, sometimes leaving blackened moss stems, sometimes leaving no trace; to be replaced by another patch elsewhere. Sometimes it was hard to see if the patches of yellow growth could count as two, close together, or one vaguely connected, or even many different patches, distributed on separate fronds of moss or stems of grass. Under the microscope it appears that even if the yellow blobs are not continuous, they are connected by a clear slime. Clearly this little area of larch woodland, open to the sky, with quite high light levels, sheltered and damp, has an active and thriving population of Fuligo septica amoebae. But exactly why, we do not know. Or maybe not thriving, and that is why they keep forming these plasmodia on the way to spore production. Maybe these populations are under stress. But because of the minute size of the amoebae it would be very hard to find out exactly what is going on.
We are only aware of the things that we see around us because they are of a size that we can see - obviously. But how often or how much, do we consider the vastness of what we can't see? We need to, because the world that we can't see is far more numerous, omnipresent, influential, dominant, resilient, and, in short, crucial, to life on earth, than us humans ever suspected.
Figure - and highlighted text - is shared under a CC BY-NC 4.0 license and was authored, remixed, and/or curated by Melissa Ha, Maria Morrow, & Kammy Algiers (ASCCC Open Educational Resources Initiative). No changes have been made.
Reference
Copyright © 2024 - All Rights Reserved - www.westcorkpalaeo.com
Template by OS Templates