Open niches

When I first learned that  mitochondria (and chloroplasts) have their own  DNA and their own personal DNA replication mechanism, I wondered if they had their own viruses that hijacked that replication mechanism.   It was a long time  coming, but it seems that there are indeed viruses that infect the mitochondria of some fungi. Obviously, this kind of thing is particularly likely in fungi.

Since living cells are exchanged between mother and unborn children,  and persist for decades, there is a possible niche for cells that are transmitted from mother to daughter, and on to granddaughters after that, and so on.  Probably to sons as well, but they would most likely be dead ends.  It is easy to show that a maternally transmitted host cell line would have to have effects on fitness that are no worse than neutral –  in practice, beneficial.

So humans could well carry a maternally transmitted symbiote that was originally human – something like canine venereal sarcoma.

This ought to be true of mammals generally, and  even if we don’t have one, some other mammalian species might.


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30 Responses to Open niches

  1. reiner Tor says:

    Before coffee I didn’t quite understand why the fitness effect for those transmitted cells should be no worse than neutral. Coffee is wonderful!

    • Richard Sharpe says:

      Wouldn’t they bias such mothers to have mostly/only daughters?

    • It is easy to show that a maternally transmitted host cell line would have to have effects on fitness that are no worse than neutral – in practice, beneficial. Because of the breeder’s equation, I ask, coffee in hand?

      • gcochran9 says:

        No. If the organism can only be transmitted vertically, from a mother to her daughters (and so on), the only way that it can persist over a long period of time is if it does not decrease carrier fitness. if it did, the line carrying it would go extinct.

  2. Patrick Boyle says:

    There is a whole series of books, films, and comic books based on mitochondria. These are Japanese works under the name “Parasite Eve”. It seems that the once free living bacteria that became mitochondria have been waiting around for the opportunity to take over from their former hosts. These rogue organelles have super powers rather like the mutants in other fiction that can time travel and mind read.

    • The fourth doorman of the apocalypse says:

      From the article:

      A single male can produce dozens of litters over his lifetime, allowing the tumor to affect many more females than it could if a monogamous species were the host. Understanding the epidemiology of CTVT will provide insights for populations that may experience CTVT exposure and information about disease prevalence.

      Now where have I heard of things like that before.

  3. Anonymous says:

    Why would it have to be originally human?

  4. Lesser Bull says:

    Could be an alternate explanation for the individuals with differing sets of DNA that has got the popular press in a tizzy about chimeras. Would be really easy to tell once someone asks the question.

  5. kingofmen says:

    > Obviously, this kind of thing is particularly likely in fungi.

    Not obvious to me. Could you expand a bit?

    • gcochran9 says:

      Cytoplasm can flow between cells in fungi. This facilitates transmission of mitoviruses: they don’t have to go through a cell wall or membrane every time in addition to the mitochondrial membrane.

    • melendwyr says:

      If I remember correctly, there are fungi in which there are no divisions between cells – just segments containing multiple nuclei. These nuclei aren’t even necessarily genetically identical – infectious fungi can derive benefits from having different traits expressed in different regions of itself, so it’s something like a cross between a population and a single individual. When our cells begin manifesting different genotypes, we call it cancer – it’s the status quo for those fungi.

  6. j3morecharacters says:

    There are cases when one twin is reabsorbed in the utero and survives as a tumor in the body of the other twin. The living twin mostly never discovers that is carrying a brother or sister in his body. The “tumor” can be neutral regarding the fitness and I can imagine ways it can even increase the fitness (say producing hormones,etc.). Monstruous but interesting.

    • reiner Tor says:

      But even if the living twin is female, her children (or anybody else) won’t inherit the sister-tumor from her. So it’s just a dead end, whatever effects it might have.

    • rightsaidfred says:

      I suppose if carrying a “tumor twin” is beneficial, then the propensity of carrying such might increase, if the thing is in any way a heritable trait.

    • Cloudswrest says:

      Kind of like Kuato in “Total Recall” huh?

  7. The fourth doorman of the apocalypse says:

    I used to think that The browns in the Mote in God’s Eye were highly improbable.

    Then I noticed that birds don’t learn how to fly. It is encoded in their genes after millions of years of selection for flying. Human babies don’t learn how to walk. What we call learning to walk is just the fact that that, like birds, the equipment is not ready until they have matured a bit.

    • Richard Sharpe says:

      I suppose that next you will tell me that religiosity and political ambition have been selected for.

      • Greying Wanderer says:

        In an environment containing a religion which preachs a set of behaviours which are net adaptive wouldn’t religiosity be adaptive as a consequence?

        (And vice versa if a religion preached a set of behaviours which were net maladaptive.)

      • reiner Tor says:

        if a religion preached a set of behaviours which were net maladaptive

        Such a religion wouldn’t survive for a long time. Because the most reliable method of transmitting a religion is from parent to child. Other methods like military conquest etc. also require that the religion not be too maladaptive.

        Of course, sometimes maladaptive religions can be around for some time, like Mazdakism in Persia in the 5th century or liberal humanism in the West in the 20th and 21st centuries. Such religions won’t be around for a long time, precisely because they are maladaptive.

      • reiner Tor says:

        (And originally I understood Mr. Sharpe to have written from the great Middle-Asian city called Sarcasm.)

      • athEIst says:

        For Reiner Tor
        I understand what is maladaptive about 20th and 21st century liberal humanism. What specifically was maladaptive about Mazdakism?

      • reiner Tor says:

        Abolishing marriage and introducing free sex for all, abolishing private property, just to name a couple of their least sound ideas. Some sources state that they wanted to reduce the army (they were pacifists, and apparently haven’t heard of the old adage “if you want peace, prepare for war”), and greatly reduced grain reserves by handing them out to the poor (thus leaving nothing for an emergency, like a drought or a war).

      • Clark Cooper says:

        That (religiosity is selected for) is the thesis of Nicholas Wade’s “The Faith Instinct”.

    • james toney says:

      many linguists, psychologists, anthropologists, biologists, etc. were baffled when Chomsky made this pretty simple point:–.htm

      good overview (which will also make you laugh or weep at the state of contemporary television):

    • albatross says:

      The fun version of this is raising bird dog puppies. A very young puppy will instinctively lock up on point when playing in the yard–our puppies would point bees, butterflies, anything interesting. That was already burned in. You still had to train them to become good bird dogs, but the genes stacked the odds in your favor.

      Another version of this is watching an untrained herding dog (a Border Collie, say) herd a bunch of small children she’s playing with.

  8. Greying Wanderer says:

    reiner Tor
    “(And originally I understood Mr. Sharpe to have written from the great Middle-Asian city called Sarcasm.)”

    Yeah i like to be blunt 🙂

  9. Dale Force says:

    First human chimera I heard of was a woman, whose husband had their children tested when they got divorced. The kids were his, but not hers (the absorbed twin supplied the ovaries).

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