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Horizontal gene transfer via retroviruses that change an organism's germ line DNA exist, even in humans, and account for a minority but not insignificant portion of the genomes of many, if not most, species on Earth.

Would it be viable to have an organism in which horizontal gene transfer was a normal and expected part of the life cycle of a multi-stage organism?

For example, at stage one, the organism would have just a bare minimum genome. Some stage one organism that survived to adulthood might then receive a retrovirus causing it to become a stage two organism (perhaps facilitated by state two organisms themselves with a sexually transmitted or blood transfused retrovirus). Some stage two organisms, in turn, might receive another retrovirus causing it to be a stage three organism (perhaps facilitated in a similar way by stage three organisms).

To be clear, I know that this is not what is going on in multi-stage organism that are familiar to us like frogs and butterflies. I'm simply asking if there is any reason that this couldn't be biologically viable.

My motive for considering this is that it might reduce mutation rates in DNA associated with later stages since fewer organism would have the later stage, in an environment that was highly prone to mutation such as one with mutation encouraging chemicals and/or radiation present at high levels), but ultimately that is just background. (Also, it is just a cool idea.)

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  • $\begingroup$ Please limit yourself for one question per post. $\endgroup$
    – sphennings
    Aug 20, 2017 at 22:28
  • $\begingroup$ Revised accordingly. $\endgroup$
    – ohwilleke
    Aug 20, 2017 at 22:32
  • $\begingroup$ I note a related post at worldbuilding.stackexchange.com/questions/84206/… but it does not seem to be a duplicate as it is asking about terminology rather than viability/reality-check. $\endgroup$
    – ohwilleke
    Aug 20, 2017 at 22:40
  • $\begingroup$ While I really like this question, its kind of hard to answer. If you assume earth-like organisms it sounds very unrealistic, but for aliens, where DNA/genes/heritable information might work differently? Sure, why not. Another problem is that HGT is defined as transfer between different species, so a transfer from stage 2 to stage 1 does not work (its unconventional, but not actually HGT) and how else are the stage 2 organisms still similar enough to each other to be considered the same species? $\endgroup$
    – Nicolai
    Aug 21, 2017 at 20:06
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    $\begingroup$ Consider the Role of "Tree of Life" in Larry Nivens' excellent works - the 'Pak Protectors' were an example of a 'third stage' transformation, and resulted in radical physiological and psychological changes that were essentially to maintain and preserve a specific bloodline. Yours seems to be a similar ( not same) situation. $\endgroup$
    – Joe
    Aug 22, 2017 at 15:51

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It's.... possible to use HGT to "clean-up" a genome, but you'd have to come up with a way for there to be a motivation for both sides to participate. They could be tied together by the transfer, but then that becomes a form of symbiosis

When bacteria use HGT, it's to spread immunity to various environmental factors to each other, namely antibiotic-resistance so far. But I wouldn't doubt if they also do it to spread the abilities to consume different foods or more efficiently dispose of wastes either.

However, because it's done through consumption for plant-to-animal and bacteria-to-animal transfers, there's the chance that your version might just recreate mitochondria. I think it would be hard to reliably use HGT to be involved in every random mating on anything higher than a microworm unless you have something that only targets germ lines specifically in a larger organism. That makes it more of a sexual parasite, which could engender specific effects in the host to help itself spread, which could give an advantage in the environment, but otherwise, I think it'd be hard to just have happen, because it might act too randomly across the population. So... what effects do you want the HGT to protect against or for then you can work it backwards to see whether it works better as a case of selective adaptation via HGT (by removing all other options to get rid of the random non-HGT mediated matings).

In which case, that might mean the HGT is behaving more like Wolbachia (which incidentally also uses HGT with other bacteria to keep up it's adaptations) bacteria, than what you're after directly.

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  • $\begingroup$ I was thinking of something more along the lines of a biological version of CRISPR. I'm not sure why there would need to be a motivation for both sides to participate. Aren't parasites one sided? Why would HGT have to be mutual? $\endgroup$
    – ohwilleke
    Aug 24, 2017 at 0:13
  • $\begingroup$ I was originally thinking of some kind of CRISPR function. But since you specified HGT I kept it at that. Parasites are one-sided, because of that, their hosts fight them, which doesn't seem like something you want in this idea of yours (I'm assuming). Wolbachia is a sexual parasite, butterflies adapt to become male despite a Wolbachia infection, the Wolbachia counters by overcoming that adaptation. It either kills males as larvae, feminizes them, promotes virgin reproduction in the females, or prevents infected males being able to mate with females with the wrong variant of Wolbachia. $\endgroup$
    – Amut
    Aug 26, 2017 at 3:35
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    $\begingroup$ That being said, I don't think your idea is impossible or unrealistic. I'm sort of paused on how to enable the jump from phase one to phase two and so on, through HGT or CRISPR reliably enough to make a species out of it. Unless, a lot of mutation or misapplication of the HGTis going to be a given. Perhaps for a world with wild seasons (a steep axial tilt perhaps) high genetic variability would be a good thing so a non-precise but additive inclined version of HGT would be quite workable I think, $\endgroup$
    – Amut
    Aug 26, 2017 at 3:40
  • $\begingroup$ First, CRISPR is a biological antimicrobial tool, adapted for genetic engineering. Second, it is misleading to say organisms 'use' HGT, since it is caused by some variety of viral infection, not a driven process. I do agree you would need something like CRISPR to make this work. It makes more sense as a stage of reproduction (say, infect a sentient on a new world, harvest virus from them and transfect your offspring so they have genes of the new host and can perhaps mimic them). CRISPR does allow for some sort of active acquisition of a new trait in a mature organism. not easy, though. $\endgroup$
    – DWKraus
    Apr 3, 2020 at 0:39

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