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I want to create a fungal organism that feeds off of radiation from nearby stars and replaces cells within the body of other organisms with modified copies. The planet on which this fungal organism exists is near the end of its life-bearing days. The planet was once much like earth, with a molten core and highly diverse complex life. The planet's core has slowly cooled over the millenniums and as a result, the magnetic field has slowly degraded causing the ozone layer to thin and developed holes. This, consequently, has allowed more and more radiation harmful to native life to reach the planet's surface. Some life has adapted to survive the higher levels of radiation but most have gone extinct. One such surviving organism, a fungus-like species, has evolved to be Radiotrophic. This organism, which will henceforth be referred to as Fungancer, takes over animal and plant life by infecting them with spores. Once these spores gestate, they begin slowly replacing the animal's cells with duplicates that are part of the Fungancer organism. (These Fungancer cells will be functionally indistinguishable from their originals with the only difference being that they are controlled by the Fungancer) This process continues until every cell in the body is replaced, sparing only skeletal structures. Once this process has completed, the Fungancer-animal/plant will grow umbrella-like protrusions from the top and sides of the organism and move to locations where they can absorb the most radiation possible. If two Fungancer-animals/plants come into contact, they may absorb each other to create an amalgam organism.

In response to DWKraus's answer, who brought up the immune system, I would like to add that the infected animal would be suffering from radiation sickness to some degree. This would cause its immune system to be weakened.

Is such a species plausible? If so, does it have any precedent on Earth?

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    $\begingroup$ A horrific but not important side-note: During the replacement process, the animal will slowly lose control of its own body, and depending on the origin point of infection, the host can remain conscious for days, weeks, or even months. $\endgroup$ Sep 21 '20 at 15:53
  • $\begingroup$ Is the fungus limited in the number/types of species it can consume? It already seems like a stretch that the fungus would have the ability to functionally mimic every type of cell in a complex organism, like neurons, skin cells, blood cells, liver cells, etc. Having the ability to mimic other cell types found in very different organisms, like plants or other fungi, would mean that the Fungancer naturally encodes a ridiculous amount of genetic potential. $\endgroup$ Sep 21 '20 at 16:05
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    $\begingroup$ It may be more plausible for such an organism to specialize in muscle, tendon, and ligaments only. It doesn't need the rest of the host to achieve its goal. $\endgroup$
    – rek
    Sep 22 '20 at 15:41
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    $\begingroup$ It might need other tissues just to keep the organism alive long enough. If it consumes the kidneys but doesn't replace them with a substitute, that specimen has a life expectancy of hours. The liver, about the same. Is it ignoring those? Does it absorb-consume 100% of the organism, or just some? $\endgroup$
    – John O
    Sep 22 '20 at 21:17
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    $\begingroup$ @MintySweeTea That being the case, it's going to have to have some novel mechanism to differentiate its cells to match (somewhat anyway) the tissue it is replacing. It's not clear what such a mechanism would be... it could maybe consume the DNA of its host and use that somehow to replicate the functionality. But this would limit it to parasitizing only organisms from its own biosphere. Xenoparasitization's probably out at that point. And even within its own biosphere, there'd still be plenty of failure modes. $\endgroup$
    – John O
    Sep 23 '20 at 13:25
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My proposal is a little different from what you described but I think it may still be of value.

Ionizing radiation is a very difficult to use as an energy source, but may serve better as a digestion technique. In our stomach hydrochloric acid dissolves food by breaking chemical bonds, converting complex molecules to simple ones. To keep the acid from digesting us we have a special lining on our stomach. Ionizing radiation acts similarly. It gets its name from its ability to eject electrons from valence orbitals in atoms and molecules. In molecules this can often lead to scission (i.e. the cleaving of molecular bonds).

A fungi may evolve a protective organelle to encapsulate radioisotopes and direct energy (through a simple opening in the cell wall) at the target of digestion. This would break down chemical bonds and effectively "digest" the tissue. The products of this digestion could then be absorbed. This is similar to how fly's vomit on their food then eat the externally digested mush. If the hosts immune system destroyed individual fungi cells the radio isotopes would be released resulting in radiation poisoning of the nearby tissue (because the protective encapsulation would be destroyed as well). This would allow surviving fungi cells to continue to propagate.

However with a limited supply of radio isotopes the fungi would cease to multiply. So evolving some mechanism which caused the host to seek out radio isotopes and consume them would be necessary.

As for what the protective organelle would be made out of? Polyethylene! To quote the wikipedia link:

In a 2002 NASA study, it was determined that materials that have high hydrogen contents, such as polyethylene, can reduce primary and secondary radiation to a greater extent than metals, such as aluminum.[27]

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Cant we all just get along?

I propose your fungus develop as a thick cake like coat on the exterior of the organism. It does not take over the organism because it is a fungus and it is bad at being an animal. But it is good at being a fungus and great at harnessing radiant energy. When it is getting a lot of energy it might exude some happy juice for the host, rewarding it for finding a good place. It might sometimes take a little protein from the host.

The host in turn is armored against hard radiation by its fungus coat and so has a fitness advantage. It can stagger around doing its animal things for longer because it fails to die from radiation poisoning. Everyone wins!

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Emerald Cockroach Wasps:

The problem of replacing your host slowly is that this is exactly what your immune system is designed to prevent. A disease that slowly displaces the host will be recognized as foreign and the body will aggressively fight it. Cancer is able to do what it does because it IS you, and is as such identical immunologically to you. Even in this, the newest generation of cancer treatments use the bodies immunology to kill off the tumors.

The tissue displacement is a little more complex than it needs to be. Simplicity works in your favor, and the natural examples are all less complex. Plus, fungus isn't usually motile (yes, there are rare exceptions depending on your definitions). In nature, taking control of your host is sufficient to get what you want. My favorite ghoulish example is the Emerald cockroach wasp. This video is a great example of what a species can do. A cockroach's willpower is overwhelmed and it becomes a zombie at the direction of the wasp, which then lays an egg that eats the pacified roach alive.

Your fungus could easily get what it wants by triggering a host to seek out high places. Other parasitic diseases have been known to cause hosts to engage in risky, suicidal behavior so the parasite is spread to what eats the host. Rabies causes infected animals to develop hydrophobia, for example.

So after your infected host climbs to a high, irradiated place and sits passively until it dies, and your fungus can continue to spread throughout the body - not replacing the tissues body-snatcher style, but through good-old-fashioned growth. The resulting fungal colony (supplied with abundant nutrients) might even look just like the original host's corpse, plus the fruiting bodies. Elevation will work well spreading spores, as will potential scavenger-predation of the bodies. More future corpses for the fungus. There may even be an attractant to draw more predators in to be infected.

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  • $\begingroup$ I'm not well versed in the immune system. Would I be correct to assume that radiation sickness would weaken the immune system of animals? $\endgroup$ Sep 22 '20 at 11:36
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    $\begingroup$ @MintySweeTea Acute radiation syndrome (also known as radiation sickness) its the result of the exposition of high amounts of ionizing radiation, in a short period of time, this causes DNA damage that may be irreparable, en.wikipedia.org/wiki/Acute_radiation_syndrome there are a lot of signs and symptoms, the DNA damage can produce chromosomal aberrations, and the overall damage on body it depends on the amount of absorbed radiation. $\endgroup$
    – DG79
    Sep 22 '20 at 15:12
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    $\begingroup$ If the fungus can survive they have an exotic biology that can use the energy resulting by cells damage, replacing cells with own modified cells requires a large amount of energy, usually a living creature didn't waste energy to do something that are useless, in nature (also exotic like that) this type of process is to parasitize the host for his energy reserve and his type of ecology $\endgroup$
    – DG79
    Sep 22 '20 at 15:17
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No and yes

A while ago when I read about this I worked out the amount of energy in radiation for the fungal cultures, and it's absurdly small - nowhere near a "Calorie". I'm feeling too lazy to look up the paper's numbers and work it through again, but for now let's just consider that a very dangerous dose of X-rays for an old-fashioned fluoroscope would just barely make a phosphorescent image viewable in a dark environment, while full-on sunlight produces a modest amount of power.

Nonetheless, your organism is a classic "Thing" that can copy an organism at the cellular level. To be "functionally indistinguishable" from other cells they must take in glucose and other nutrients such as nucleic acids, and reduce them to CO2 and water and other relevant wastes such as uric acid. Provided they can steal the information to do what normal cells do, they certainly can do what normal cells do. The "radiotrophy" would just be a symptom - perhaps applied like the hot wire in the original Thing used to recognize the presence of the invader, or nominally explaining the sustenance of the fungus during a long interstellar flight inside an asteroid.

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It should be a virus, not a fungus

"Replacing the host cells with its own cells that are functionally indistinguishable"...yeah, not going to happen. To mimic the functionality of a cell your organism will have to have the same DNA of the cell it's trying to replace. It will need to have the potential to transform into any cell on the planet (implausible) or it will need to somehow copy the host's DNA (in which case it is not really its own species anymore).

What you really want is something that can take over the host's cells, leaving them in place, but adds additional behaviors or functionality. This is what viruses do, though a virus such as yours is an incredibly complex one (most viruses add no functionality apart from giving cells the "ability" to construct new viruses). Perhaps the virus's ancestors once infected a radiotrophic fungus and assimilated some of its genes before jumping over to infect animal life. This virus might contain the DNA needed to construct organelles that can absorb radiation and convert it into usable sugars, or even convert specific types of cells into the larger structures you want it to turn into.

The idea of a single organism being able to infect numerous types of plants and animals is unlikely, but they might be variant strains of a single ancient ancestor that evolved to infect different kinds of life. On a planet where radiation was a significant threat, this virus might convey a strong benefit to its hosts, and this would serve its own survival and allow it to proliferate.

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