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Mycolaria is my working name for an alien planet featuring a much more visible role for fungi of all kinds, large and small. There are also animals and plants on this world. This is the second in a series of fungi-related worldbuilding questions.

This particular mushroom related question is about radiotrophic fungi, which are able to make use of radiation via Melanin to power their own growth. These have been observed on earth, e.g. at Chernobyl.

I am looking for input on whether/how an animal species could enjoy a symbiotic relationship with radiotrophic fungi so that they can survive in a planetary environment which is afflicted by levels of surface radiation anywhere between 3 and 100 times that experienced on earth.

While an affirmative answer may well not be forthcoming, I am interested in biological issues surrounding this question.

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3 to 100 times Earth background is not a lot. The world average is about 3mSv per year. People in places like Ramsar, Iran have a yearly dose of up to 260 mSv with no reported ill effects. You will need to bump that up even more so you end up at around at least 1 Gy/year. But that is just petty details... you can pick an arbitrary number.

To your question: the beneficial effect would be...

  1. the symbiotic partner can make use of the fungi's DNA repair mechanisms. Some species have exceptional DNA repair and can survive massive doses thanks to that. The bacterium Deinococcus Radiodurans ("Terrible berry that endures radiation") can survive doses of radiation that are 5000 times higher than what causes acute radiation sickness in a person.

In your universe, you can have a fungi that allows the symbiotic partner to make use of this repair mechanism for themselves.

  1. the fungi can have a shielding effect by hosting substances that have a high nuclear cross section. This would be useful if you had natural neutron radiation.

EDIT: As requested, let us go deeper into this.

Actually what you wrote in your original post is hitting close to the truth already. There has been some interesting research results from the Chernobyl area that suggests that animals can actually adapt to a higher-than-normal radiation environment. And it is assumed that anti-oxidants is the key.

Bank Voles - who have now bred for over 50 generations in the area - show no ill effects of living there. They even show slightly higher then normal resilience when subjected to even more radiation. It is thought that anti-oxidants play a key part in this. The radiation is causing oxidative stress and the vole's body responds with producing more anti-oxidants (or as the article suggests: producing less of red/pink pheomelanin that otherwise use up anti-oxidants). You can read more about it here.

In your world, the fungus may have its own version of photosynthesis - or in this case perhaps we should call it radiation-synthesis - that make use of the highly energetic radiation photons to produce a surplus of particular anti-oxidants that can be absorbed by the symbiotic partner and put into use to defuse the free radicals caused by radiation before they can damage DNA.

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    $\begingroup$ "the symbiotic partner can make use of the fungi's DNA repair mechanisms." Yes that is exactly what I am after, but you have not set out how the animal host's damaged DNA actually gets repaired by the radiotrophic symbionts properties, assuming that the animals dose of radiation is in the 1-50 Gy/year. If the animal DNA is separated by a cell membrane from the fungi cells, how can they repair it? If you can answer me that the bounty is yours! $\endgroup$ – rumguff Sep 4 '15 at 23:25
  • $\begingroup$ Allright... made a quickie addition. In brief: anti-oxidants. If your fungi produce a particular kind of anti-oxidants - or a lot of them - they can mitigate the oxidative stress that radiation causes. $\endgroup$ – MichaelK Sep 5 '15 at 2:47
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A lot of radiation induced damage to DNA doesn't come from "direct hits" of the DNA. When ionizing radiation hits water it forms peroxides which are fairly stable in the body, but which can then form hydroxyl radicals. These super-reactive molecules can then cause damage to the DNA if they come into contact with it. All of this information can be found here: https://en.wikipedia.org/wiki/Free_radical_damage_to_DNA. While this isn't directly related to melanin, high levels of radiation will cause the formation of lots of these peroxides and its possible an organism could utilize them as energy. This paper suggests hydrogen peroxide was an energy source for early self-replicators. A symbiotic fungus that efficiently scavenged the harmful hydrogen peroxide molecules from an animal could reduce the mutation rates in that animal substantially while also deriving energy from the molecules.

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  • $\begingroup$ Thanks Mike, but I don't seem to have access to the linked paper. Are you suggesting that the fungal cells are going to float about in the water content of the animal body and suck up the peroxides from within, so to speak? $\endgroup$ – rumguff Sep 4 '15 at 23:30
  • $\begingroup$ While that would be one option, the fungus actually living within the tissues of the animal, I was thinking more like the fungus acting as something of a filtration system for the animal's blood or other fluids. It could live on internal membranes like our symbiotic gut bacteria, or if the animal is something like an amphibian with a permeable outer membrane the fungus could live on the exterior. Either way the fungus is sort of like a dialysis machine machine that filters out harmful mutagens for the organism. $\endgroup$ – Mike Nichols Sep 5 '15 at 0:22
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The trouble with radiation is that it gets everywhere. Sure, you may have a 'fungus' that can fuel its metabolism with radioactives, but whatever it is in a symbiotic relationship with would have to be similarly radiation-resistant. Radiation isn't going to always pass through the fungus first.

I.e. don't expect a human - or his dog - to be able to get infected with this stuff and be any less vulnerable to radiation poisoning while their immune systems try to fight off the alien invader in their bodies. A terran plant - since their immune systems are so basic - is a possibility for an alien symbiosis. Pretty much any organism that this 'fungus' is - or could be - a symbiote with would most likely have evolved alongside it.

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  • $\begingroup$ "Radiation isn't going to always pass through the fungus first." It would if the creature had a decent outer coating of it over its skin. That was about all I managed to come up with so far. $\endgroup$ – rumguff Sep 2 '15 at 7:06
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    $\begingroup$ @rumguff, not if the creature ingests it, or if we are talking about gamma radiation. $\endgroup$ – Monty Wild Sep 3 '15 at 0:42

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