Ten-legged inbreds.

Discussion in 'Physiology and Biology' started by neurobadger, May 7, 2011.

  1. neurobadger

    neurobadger Vampyroteuthis Registered

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    So I live in DC and I went to the National Zoo on a day off.

    They have a really old male cuttlefish - 20 months old, which is a Methuselah of a cuttlefish - and he sired offspring, three of which apparently survived, a male and two females.

    They did not know this until the male impregnated his sisters.

    No good can come of this for the cuttlefish (it's like cephalopodian Deliverance).

    At the same time, I am almost morbidly curious to see what kind of deformities come from this and what it can tell us about cephalopod genetics in general, since presumably octopuses, cuttlefish, and squid share a massive amount of genes.
     
  2. DWhatley

    DWhatley Cthulhu Staff Member Moderator

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    I had inquired about inbreeding octopuses when my O. mercatoris hatchlings came of age (no oddities or life span issues noted in first generation sibbling matings) and the reports I received back were that there does not seem to be known issues until ~9 generations (this was a "think I remember number" from observations coming indirectly from work at the NRCC so it is hearsay) in officinalis. Thales might have a better direct observation.
     
  3. Level_Head

    Level_Head Vampyroteuthis Registered

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    As both of you can imagine, I developed a special interest in this topic. (Not to spoil any plot elements for non-yet-readers...)

    The understanding that I developed was that there was a heightened chance for positive reinforcement of bad alleles, which would be represented in a percentage of the offspring. But in general (not specific to cephalopods), the effect is to breed these bad alleles out of the population rather more rapidly than is the case with normal heterogeneous mixing.

    Some zoo populations were looked at extensively, as examples of inbreeding with often meticulous (though not perfect0 records. The results were gathered in Chapter 15 of this book (pg 352):
    http://books.google.com/books?id=ZFXYeHxwD10C&printsec=frontcover&hl=en#v=onepage&q&f=false

    The upshot is that there's generally an effect, it's generally (but not always) bad, but some of the bad effect is actually outbreeding (among subspecies) rather than inbreeding, and that the data is not clear enough to draw hard conclusions. They suggest that the usual effect is higher infant mortality -- and for our purposes, such an effect might not even be noticed in aquarium settings as the failure rate of large-egg species is often in the tens of percent anyway.

    And if one is content to deal only with the survivors, and to withstand a higher than usual deformity rate early on, such an arrangement is potentially viable. It reduces random variations to an extent, leaving local mutations rather than diverse contributions from outside sources.

    This is considerably less effective as a variation creator. With inbreeding of siblings, you get only the mutations of the single generation (plus whatever is "new" in up to half of the genes not already part of the other sibling). But in outside mixing, you're getting mixing of mutations (successful or neutral) that have built up over however many generations since the last common ancestor.

    So, it's not a great deal for creation the variation that natural selection works from, but it does not eliminate such variation.

    Back to the book linked above:
    The authors also suggest that it's difficult to extrapolate the effect of inbreeding on humans and domestic livestock, with thousands of years of unnatural selection, to wild populations.

    Other chapters in the same book pursue the topic from different angles.
     
  4. Mike Bauer

    Mike Bauer Vampyroteuthis Registered

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    Cool topic! Interesting reading.

    Thanks
     
  5. Level_Head

    Level_Head Vampyroteuthis Registered

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    The book linked above continues to be interesting. And amusing -- this is from Chapter 18:
    Sounds like this fellow may have had some encounters with all of these creatures -- and not always successful encounters.
     
  6. neurobadger

    neurobadger Vampyroteuthis Registered

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    Weeeell, I'd say the second entry in the latter group has very good reason not to do so if an individual within the group so chooses, but that's another discussion.

    I know there's a fairly high probability of deleterious mutations with regard to inbreeding in mammals, at least.

    (Various royal lines are a particularly illustrative example of this; one Habsburg king of Spain had such pronounced prognathism that he could not eat, and he was also mentally retarded.)
     
  7. Level_Head

    Level_Head Vampyroteuthis Registered

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    True -- but royalty is a poor source of data, as they have retainers to anecdote over them. ;)

    Moreover, the references above make explicit that the human experience is not reliably able to be extended to the larger mammalian world, let alone the animal and plant kingdoms.

    One of the articles makes the point that the populations who generally inbreed -- there are many such -- typically are of small body size and high population count. The larger the individual body mass, as a very general rule, the less likely inbreed is to be common. But of course there are many exceptions.

    In most places, we'd be interested in the human aspects of this. But here on this thread, it is the cephalopod implications that are most important to us, for different but related reasons.

    Something occurs to me, though: Did encountering this topic put you off finishing Age of Octans?
     
  8. DWhatley

    DWhatley Cthulhu Staff Member Moderator

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    In-breeding in humans is not as uncommon today as I once thought. I have a friend who came from a rural area in India where marrying one's uncle (father's brother) is considered desireable. She refused this kind of match but her sister did not.

    With cephs, there are often multiple fathers in a wild mated brood so first generation in-breeding with wild mated parents may be diluted to the mating of half sibblings rather than carrying only two sets of genes. However, the low egg survival in my current group might be accounted for, at least in part, by the brother-sister match up.
     
  9. neurobadger

    neurobadger Vampyroteuthis Registered

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    Nah. I read it all the way through. I thought it was pretty good!
     
  10. Level_Head

    Level_Head Vampyroteuthis Registered

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    The Wikipedia topics for incest and "incest in popular culture" are interesting. I had no idea how "popular" it was in science fiction, nor was I aware of the short story "If All Men are Brothers, Would You Let One Marry Your Sister?"
     

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