User blog:Cerne/Radiophage reproduction and symbiosis

Here is yet another section of my Part 2 update that couldn't fit into the entry and hence had to be separated. I am thinking this is technically an entry in its own right and not actually an update. And actually, I could say the same about the previous two entries as well; there is updated information, but there is also new information that I felt I needed to add to support the subject matter and make it more substantial. That includes this entry. So, yeah, not really an update per se... In fact, I don't think I am going to title another blog entry as a generic update of my conworld unless it has short, bried summaries of what I've decided on and how far I've gone up to that point, Then I may bring up where I plan to go with it and where I plan to get the supporting info. What I have here is something that once was a brief update summary and has turned into an end result once I'd already done the research. I shouldn't be doing that for an update. Hopefully my next entry - which was also once going to be a segment in my Update part 2 entry - will reflect that.

But without further ado, here is THIS entry.

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A few entries back (quite a few, actually), I brought up a group of organisms that were supposed to be a fifth kingdom of life on my planet. This “kingdom,” if we may call it that, is a group of organisms resembling plants in the sense that they are autotrophs: they synthesize their own food in the form of sugars as well as their own organic tissue in the form of complex hydrocarbon chains. And yet, a few of their qualities are more like those of fungi: they will “eat” organic matter and absorb other types of matter rich in hydrocarbons. They will even recycle themselves; that is, when one organism dies, others will grow on it and inside of it until all dead organic matter has been absorbed and/or replaced with living tissue. I do not yet know what to call these organisms. Radiosynthetic “plants” does not seem completely appropriate. Maybe “Radiophagia?” I don’t know. But anyway, I’ve already told you how these things synthesize organic matter. But aside from discovering that it may be possible to create Epsom salts out of stabilized alkali metal isotopes and sulphur (this will be brought up again later), nothing else has been thought about or changed so far. Now, two other problems arise: reproduction, and symbiosis/co-evolution with other organisms.

Okay, so since these radiosynthetic organisms are descended from primitive autotrophic micro-organisms and their reproductive strategy hasn’t changed much since then, you would expect something involving spores and probably some sort of alternation-of-generations. Well, this is true; moreso, the gametophyte generation – the “generation” of organisms that produces sperm and ova – is less noticeable than the sporophyte generation which produces spores. In particular, the first gametophyte generation lives mostly underground or fastens itself to rock walls, with its root-like rhizomes acting in much the same way that vines on Earth cling to trellises, and in most species there only needs to be one gametophyte generation per organism. However, in some species, there is more than one gametophyte generation and this is when things get bizarre.

The sporophyte generation starts out as a diploid zygote and grows within the gametophyte’s archegonia because that is where the ova are produced. First-generation gametophytes are monoicous so they produce sperm and ova together, but once their sporophyte offspring start growing, the gametophytes become male. They can no longer produce ova because the newly-grown sporophyte fuses with the surrounding archegonia in the parent gametophyte, but the antheridia can still function. Once grown, the sporophyte can start producing spores; it grows branches that have pods on the end, and these pods induce chemical reactions which allow them to burst open with spores. Once this happens, the gametophyte generation needs to reproduce again before the sporophyte generation can produce spores. This isn’t that much different from the reproductive strategies of ferns and mosses on Earth: gametophytes grow from spores and are typically monoecous first, then becoming unisex (either male or female) later, and – upon being fertilized by another gametophyte – give rise to a sporophyte generation that grows above ground and produces sugars for the plant via photosynthesis. The fronds on a fern are the part of the plant where photosynthesis and sporogenesis (spore production) take place.

The first thing that makes these radiosynthetic “plants” unusual is that the ova produced by the gametophyte generation are produced in clusters within a single archegonium and can all be fertilized at once (with multiple sperm, of course). The clusters equal roughly the number of rhizomes the gametophyte has, give or take one or two in some cases, and this trait has evolved from the more primitive strategy of reserving one sporangia per single sporophyte and having the spores disperse one sporangia at a time because these organisms have hexagonal symmetry; multiple rhizomes come from a single centre that makes up the gametophyte’s prothallus and each rhizome has its own antheridium and its own archegonium. But while the antheridia are separate, with one antheridium per rhizome, the archegonia are fused together into a single archegonium. So, it makes sense that the organism would produce a single cluster of multiple ova rather than sticking to a single ovum per many archegonium and having those sporophytes evolve toward having multiple sporangia. However, I will say here that there are some species which have multiple sporophytes growing out of a single gametophyte. These are just not as common, and are not as conducive to having the large tree-like structure I was looking for in the species in question.

The second thing that makes the radiosynthetic “plants” unusual (as far as plants are concerned, anyway) is that the gametophyte generation is physiologically dominant in the organism as a whole; the gametophyte generation does more for the organism as far as support goes – providing the means and the materials by which inorganic molecules can be converted into sugars and organic matter as well as forming the foundation for new growth – than the sporophyte generation does. The gametophyte generation also [bears] most of the actual growth so it makes up most of the organism’s biomass and hence is comparatively bigger, though rhizome circumference may not be a good indicator of this.

For the most part, the inter-relationship between generations in these organisms is like that of ferns on Earth: the gametophyte typically grows separately and the sporophyte grows as a dependent. Where the dynamic of this inter-relationship reflects a more primitive arrangement as seen in mosses and other bryophytes is in the way by which the organisms reproduce sexually. Like all spore-producing plants on Earth, the radiosynthetic “plants” here require water in which to carry their sperm to other plants. But given that they often grow on cave walls, cliff faces and other places with little or no loose substrate, they need some way in which to physically connect to other plants or grow so close that their sperm can actually reach another plant. How they manage to grow so close enough to each other in the first place for this to happen, I do not yet know, but the result would be a sort of communal reproductive strategy. Much like that of moss. The air they grow in may need to be still and stagnant so this brings up the idea of gradual population growth from a single area instead of sporadic growth in a bunch of new areas farther away from the parent population. Some species could become parthenogenic or evolve a “grassroots” strategy, but not the species I am thinking of here.

The third thing that would probably be considered very unusual amongst plants in particular – and thus arriving at the crux of what I suggested earlier – is the phenomenon of having multiple gametophytes growing on the same organism. Angiosperms on Earth can have multiple gametophyte-producing organs on the same plant but the gametes they produce don’t actually grow on the parent sporophyte. They grow separately until they are dispersed as pollen, after which they fertilize – or are fertilized by – other gametes from other plants, and then grow into diploid seeds that become new sporophytes. In a way, angiosperms have surpassed the sporophyte stage altogether and have evolved toward sexual reproduction exclusively; spores growing into pollen are much like cells growing into other parts of the plant, albeit at a different stage in the plant’s development, so I personally don’t even know why people say that angiosperms still go through an alternation of generations.

Anyway, on the radiosynthetic “plants” that I am proposing, multiple gametophytes grow well beyond macroscopic size and remain “grafted” onto the parent sporophyte while they reproduce and then disperse new sporophytes, again inside of – and then growing out of – the same organism.

None of this should make sense to you right now because I’ve previously described how gametophytes grow on rocky surfaces and require water to reproduce sexually. I’ve also described how sporophytes grow from the single archegonium of their gametophyte parent. So how can both sporophyte and gametophyte grow out of the same parent organism? Well, this radiosynthetic organism – and more specifically the species I am referring to – is what we would call a super-organism. In the sense that I am referring to it right now, it is an inter-generational super-organism, meaning multiple individuals of the same species grow on each other and consequently have a different morphology depending on where they grow on the organism. The first gametophyte generation grows on the ground and has a hemichordate-like design. From that, branches with several sporophytes growing together from the same archegonium will all produce spores. They also “collect” spores from other sporophytes by growing a sticky outer layer over the collapsed sporangium and trapping any spores that happen to float by. Once trapped, the spores travel down the branch holding the sporangia and stop at the base of the sporophyte structure where all the branches meet. There, they grow into more branches. But rather than having round balloon-like sporangia, these branches have thick, sponge-like mats growing on top of them. These are what the organism uses to absorb atmospheric gases for radiosynthesis. The first gametophyte generation now no longer has the sole task of taking in all the chemicals it needs.

Again, this should not be considered completely unusual because there are several animal and fungal species on Earth that are colonial to such an extent that they are biologically integrated with each other. There is the cnidarian siphonophore, for instance, that is composed of thousands of smaller medusoid jellyfish, each individual playing their own role in the colony that we think of as a single individual jellyfish. However, I will point out that these creatures are better thought of as multiple “types” of smaller organisms that combine to make up something bigger because each of the component jellyfish are so specialized toward a given “role” that they are completely dependent on the combined “super-organism”; that is, they cannot survive on their own if by chance they were to become separated. A better analogy for the autotrophic organisms I am envisioning would be the numerous polyps – another kind of cnidarian – that make up coral reefs. Coral polyps are morphologically very similar to each other so they can survive on their own (more or less) without much trouble, and this is where I would like to make a contrast between a “super-organism” and what we call a “colonial organism.” The typical biologist may not agree with me here because these two terms seem to be used interchangeably in the literature but it becomes an important contrast for me nevertheless so I will use it. My radiosynthetic autotrophs are basically individual plants that are growing on – or out of – each other; the sporophyte generation is still dependent on its gametophyte parent, just like any spore-producing plant on Earth, but new gametophyte generations can still survive on their own. When they grow inside other hosts, the only thing that really changes is their morphology. So, rather than being a true “super-organism,” I call my radiosynthetic autotrophs “colonial organisms.”

The final thing that makes these radiosynthetic organisms unusual is their ability to change reproductive strategies within a single generation, not just a single individual with multiple generations growing on it.

You’ll remember much earlier how I said each sporophyte could only produce spores once before its parent gametophyte generation had to reproduce again. Well, this technically can’t happen; it could happen if the parent gametophyte could still produce one – or both – of each type of gamete, and it will happen in other related species, but there is no way for a sporophyte of this species to release spores more than once. I know spore-producing plants on Earth can do this because their sporophyte generations reproduce independently, but these sporophytes can’t do that. Maybe it is just one more way in which the generations have become more dependent on each other. Or maybe they can produce more spores after all, once they’re finished attracting foreign spores and have shed their sticky spore-trapping layer. This matter is still open for thought.

On the other hand, gametophytes can and do reproduce more than once. First-generation gametophytes only produce ova once and newer generations don’t produce ova at all. All gametophyte generations can produce sperm more than once but this doesn’t mean anything if there are no ova to fertilize.

Going back to the situation with the sporophytes, I’ve speculated that they could technically produce spores more than once, but that after the first time these spores would no longer grow on their own. They could, in effect, become ova. This fits in well with the alternation-of-generations strategy because what makes spores haploid in the first place is that they do not involve the fusion of a haploid sperm and ova. Ova also happen to be haploid; the only real difference between the two is that one can propagate on its own and the other can’t. There is no reason why the ability to produce spores should be halted when the spores themselves are already haploid. All that needs to happen is for the spores to no longer be viable. Would it then be that infeasible to imagine a sporophyte becoming a female gametophyte?

The problem I face now is twofold: I need to explain why these sporophytes don’t produce spores when they should be able to, and do produce ova when they shouldn’t be able to.

One possible alternative is to not make the sporophyte itself produce ova but rather have it reserve a spore which can then grow into a microscopic gametophyte at the base of the plant where it can be fertilized by the male gametophytes that have already grown at the base. This has the added benefit of allowing sporophytes to produce spores more than once.

Another alternative is to make the grafted gametophytes female instead of male and have the first-generation gametophyte somehow fertilize them internally by transporting sperm through the body of the sporophyte. This alternative is less efficient but doesn’t require me to break any current biological rules regarding how the alternation-of-generations strategy is supposed to work.

Regardless of what I end up choosing, this is where I am at right now and I am not going to ponder the questions further for the time being.

ANYWAY, once the ovum reaches the base of the sporophyte branch (if it isn’t already there), the dioicous male gametophytes fertilize them internally and a new sporophyte grows out of what is the “crown” of its sporophyte parent. The whole cycle can repeat itself over and over again until the organism reaches several stories high and has up to a dozen generations or so living on it. With the planet’s lighter gravity, the organism’s linear structure and its high carbon composition, I feel this could certainly be possible.

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Now, while I’ve gone on quite a bit about reproduction in these organisms which I might end up calling “radiophages” or something similar, I would like to go into inter-species symbiosis and co-evolution for a while before I end the entry.

If you consider mitochondria and chloroplasts to be symbionts, as entailed in the Endosymbiotic Theory of eukaryotic cell evolution, then the “radiotrophs” that I have been describing can and do count as a symbiosis between the cells that carry radioactive isotopes and split atoms of CO2 and the larger organic whole that benefits from the released carbon and oxygen that the cells produce. Aside from that, I actually tend to think of the radiotrophs as more like a lichen – a fusion of plant cells inside a fungal body – than a weird intermediate relative of plants and fungi that is a little bit of both but still not technically either. At least this way I can explain their ability to consume organic and inorganic matter at the same time. I am aware that many so-called “carnivorous” plants on Earth consume insects, but as this adaptive strategy is used to obtain nitrogen only, I don’t feel they would make a good analogy. Likewise, many epiphytes do obtain carbon from their “hosts” but I do not consider this to be the same as consuming organic matter. Rather, epiphytes are best thought of as parasites that have established the relationships they have with their hosts through a circumstantial adaptation that led to an obligatory co-existence. My radiotrophs had always been active consumers of anything organic they could find. That may even explain their symbiosis with the aforementioned radiotrophic cells. Or maybe not. It can go either which way right now.

Due to their largely anoxic chemical composition, these radiotrophs burn rather quickly and readily. This is both a curse and a blessing; while being very burnable is not a good thing, it means that lots of other organisms will want to take advantage of that and – in effect – decrease the chances of actually burning. In this case, colonies of heterotrophic fungi grow along the outside of each radiotroph’s “trunk” and consume the outer part of the phloem. In this sense, they could be considered parasites. More appropriately, though, they constitute an equal symbiosis with their host by decreasing its susceptibility to oxidation from the surrounding air. The fungi eat organic matter made up of hydrocarbons and release CO2 back into the air through aerobic respiration. So they make up a sort of living trunk for the radiotrophs.

In my previous entry I mentioned “red” plants that use gaseous sulphur to neutralize acid rain and then use the remaining H2O for photosynthesis. I also mentioned in this entry that subsequent gametophyte generations of radiotrophs have a spongy leaf-like structure at the ends of their branches. These spongy structures are made up of mostly sulphides and will release hydrogen sulphide if any amount of weight is pressed down upon them. Another symbiotic relationship involves red plants growing on these large spongy mats and using the sulphur contained within them for neutralizing acid rain in exchange for extra carbon and nitrogen as well as hydrogen through photosynthesis. The plants also help their radiotrophic host to filter in the right gases and filter out the wrong gases from the atmosphere. In effect, they act as “flood control” for the radiotroph.

Finally, all radiotrophs are involved in a co-evolutionary arms race with a group of invertebrates that have evolved in the same ancestral subterranean environment alongside them. I’ve already described them briefly in my last entry. They basically resemble segmented worms with legs; their body segments each do a slightly different task – with the first segment housing the brain, sensory and feeding apparatus,  and the first part of their long segmented stomach – and most go through an animal version of a plant’s alternation of generations strategy. These relatively specialized invertebrates are (for the most part – there are exceptions) herbivores that consume living matter from the trunks and rhizomes of radiotrophs. In their native subterranean habitat they get carbon from their food, inhale hydrogen, and exhale methane. Upon adapting to a surface environment where there is more oxygen and lower concentrations of hydrogen, however, a shift from breathing hydrogen to breathing oxygen may have been necessary. So instead of breathing any specific atmospheric gas, I envision a more generic form of aerobic respiration for these invertebrates.

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And that concludes my "former-section-now-an-entry" entry. I will definately not be able to post my final "update" entry right now. Maybe later tonight. Actually, I am kinda pressed for time right now because I am using a public computer and the building may be closing soon. Or, if not, that f***ing annoying log-off prompt will come up and kick me off the computer, like so many other log-off prompts have done before. I wish public places and businesses wouldn't use them... ANYWAY, I gotta go. Thanks for reading.