O. chierchiae evolution...

Discussion in 'Physiology and Biology' started by gholland, Mar 22, 2008.

  1. gholland

    gholland Haliphron Atlanticus Supporter

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    I wanted to continue this discussion without completely hijacking Jon's thread...

    The next question I have is whether the genetic analysis might be able to indicate when this egg-laying habit was lost (or gained) and how that timing related to the development of a bottom-dwelling life (or do I have that backwards too?) and the loss of a shell.

    Seems like you might not need to lay as many batches of eggs when you have the ability to crawl into well-hidden, easily defendable spaces. Maybe?
     
  2. monty

    monty Colossal Squid Staff Member Supporter

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    In my (limited) experience, trying to guess about things where we know very little usually turns out, while fun, to rarely match what the data shows...

    Right now, there's been very little detailed work on how cephalopod reproduction is controlled genetically, although people are starting to apply modern molecular biology and genetics tools to all sorts of animals, including cephs. As far as I've been able to tell, we don't even know what genetic (or other) controls lock an octopus into being male or female the way we understand the X and Y chromosomes in humans... in fact, Steve just pointed out an article on some South African squids where the males sometimes have some female organs and traits... another good candidate for looking at to sort out sex determination in cephs.

    So, I'm reluctant to say anything without a big "I'm just making up science fiction about this." This is still useful for science, in the sense that a lot of this sort of work involves making up a "science fiction" hypothesis based on currently known data, figuring out ways to test the hypothesis, collecting new data or re-evaluating old data to see if it matches the hypothesis, rinse and repeat.

    That being said, I can make stuff up:

    Argonauta is an interesting animal to look at in this regard. It's not clear where it fits into the taxonomic picture, and it might (or might not) represent sort of an ancestral octopus form. It broods its eggs in the shell/ egg case... it's possible that this was the original way octos brooded, and they only developed the cave-dwelling brooding behavior later. It's been suggested (as well as argued against) that the similarity in shape of the argonaut shell to nautilus and ammonite shells, even though it's from a completely different mechanism, might mean that an ancestor coleoid used empty shells from those animals to brood eggs in. I find it interesting that mercs hold their arms over their heads in ways that look (to me) similar to argonauts, and argonauts create their egg cases by a secretion from their arms. Argonauts also have the odd behavior that the male detaches his hectocotylus during mating... I don't know if he then is doomed, or if he can re-grow it and mate again.

    In any case, O. chierchiae certainly looks like it's more closely related to more familiar octopuses than to argonauts, so I'd guess that it developed this behavior more recently... it seems unlikely that so many other octo species would have lost an ancestral trait that this one species preserved, so I'd be inclined to look for a what triggers senescence in other octos by evaluating what might be different in this species.

    Comparing it to Vampyroteuthis infernalis would also be marvelous, since that's commonly interpreted as a branch off the octopus lineage that's separate from the squids and cuttles. I'm not sure how much is known about their reproduction: their larvae have been studied (they do some weird things with replacing one set of fins with another) but I don't know anything about their eggs, and I'm pretty sure they haven't been bred or raised in captivity.

    As far as the timing goes, it's common to use "genetic drift" as a "genetic clock" to find out when various traits arose, so that could certainly be done with this species and other octos. I would imagine that, since chierchiae share so many other things in common with other modern octopuses that they branched off fairly recently, so I'd expect that their reproductive oddities don't go back too far in the coleoid history, but they could quite easily be a mutation that "undid" a previous adaptation in an octopod ancestor or something like that.

    I'm also curious about pelagic and midwater octopods, in comparison to the denning behavior of those who live in shallow water which seem to favor this "all your eggs in one basket" approach... although argonauts, as mentioned above, solve that by making their own portable "den." And of course, some squids brood their egg masses as they swim around.

    There are some theories that the "macroconch" sexual dimorphism in ammonites was also a way for females to raise their eggs inside their shells (does this occur in nautiloids as well?). It is frequently suspected, although still pretty murky, that ammonites are more closely related to modern coleoids than the modern nautilus... of course, the belemnites split off quite a long time ago, and are more likely to be immediate ancestors of the coleoida, since ammonites continued for a very long time after the belemnites. I'm not sure where the very few coleoid fossils fit in, but my impression is that they're somewhat more recent than the belemnites.

    Since I just finished being overwhelmed by a class on gene regulatory states, I'd imagine a good thing to do would be to look for expressed regulatory state in some more common octopus, perhaps using the optic glad, since it's known to be a factor in sexual maturity, and look for changes in regulatory state before and after brooding, and then look for the corresponding genes in O. chierchiae and see if there are any obvious differences, and then go back to the more common octopus and see if some sort of gene transplant or knockout could induce iteroparus reproduction in another octopus. This is really hard stuff, but people are starting to do stuff like this a bit: someone studied the genes that control beak shape in finches which show a wide variation in specialized beak shapes (no doubt a tip of the hat to Darwin's having been inspired by them) and then actually tested this by seeing if beak shape in chickens could be modified by the same genetic controls, and to some extent, this worked.

    That's my :twocents: which hopefully will provide food for thought, but any conclusions about the actual relationships between these animals will almost certainly turn out to have some surprising and unanticipated results... because these things always do! Maybe I've inspired some of the people who do this for a living to chime in (and probably correct all sorts of silly mistakes I've made in the above.)

    Thanks for making a new thread for this discussion... these sorts of things are always very enjoyable.
     
  3. Steve O'Shea

    Steve O'Shea Colossal Squid Supporter

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    ... I'm staying out of this one; that's why I haven't responded, sorry.

    It would make for an interesting thesis topic, but it could be rather speculative unless handled extremely carefully, and even then it wouldn't be the definitive word on the matter (just the 'lastish' word until someone else re-evaluated it with new/novel or different tools).
     
  4. monty

    monty Colossal Squid Staff Member Supporter

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    Although I understand the need for secrecy and discretion in academia, it sure takes the fun out of things... and ultimately, I'm not positive it serves the scientific endeavor all that well...

    I suppose this raises an interesting question for TONMO... I really enjoy (and try to encourage) the "what if" discussions and such, and I like to pretend that it's useful for education and research, even though it drifts into the "silly" and/or "pointless" and/or "wild guess" areas more often than actual discussions among scientists. But is there a risk of causing problems by placing people into too many awkward situations?

    I seem to be weird in that I am a lot better at thinking of interesting research topics than actually knuckling down and doing research... I've been told that a lot of PhD students are rather the opposite (which is probably why they get PhDs and I'm an unemployed polymath), and are terrified that someone will "scoop" their few-and-far-between research topics. Should we have some sort of suggested limits or protocols here to protect everyone, encourage interesting discussion, and make sure everyone's expectations are in line?
     
  5. Steve O'Shea

    Steve O'Shea Colossal Squid Supporter

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    I'm all for open discussion Mark, but I'm just not qualified to comment on the initial question, and haven't given the subject matter any consideration. You're more widely read than I am; my interests are quite narrow in fact. Were I to make any comment on this thread I'm sure that someone with more knowledge of or interest in the subject matter would quickly correct me.

    I'm not into character polarity, whether this be genetic or morphological. I just see little point in it, because we'll never know for sure until someone builds that time machine. If someone did build a time machine I can assure you there are many more important things to do with it before anyone ever got an opportunity to use it to chase octopus around prehistoric shores for the sake of unravelling some genetic mystery ... and even if they did they'd just identify an earlier genetic mystery that needed to be studied, and so on .... right back to that first amoeba, lump of rock snot, protein molecule, or whatever it may have been. If that amoeba had a conscience I bet it couldn't sleep now, knowing what it was responsible for; it's still out there now, somewhere .... being the nasty little asexually reproducing lump of protoplasmic filth that it is!
     
  6. monty

    monty Colossal Squid Staff Member Supporter

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    Actually, I had to look up what "character polarity" means... and I apparently misinterpreted "not wanting to go out on a limb" as academic secrecy...

    I'm less interested in the academic debates of questions we can't answer, but I think there's a lot to be learned, and sometimes inferred, about both modern and ancient animals by studying the evolution of body plans and genetic controls, and I like to think that this is an interesting lens to understand how living animals "work."

    Anyway, I find that I enjoy bantering about this stuff as a way to learn things, so while I'm dubious about the value of my reading lots of, well, stuff being more relevant than your encyclopedic knowledge of the immense amount of interesting marine biology out there, I'll forge ahead but ask that you and anyone else correct my ignorance as appropriate...
     
  7. gholland

    gholland Haliphron Atlanticus Supporter

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    That was my only reason for bringing this up. As I've said, my background is chemical engineering, not biology. I've enjoyed learning about biology and genetics and "character polarity" here at TONMO and I'm basically just curious about what types of research methods are available and what the implications are. :smile:

    Information with disclaimers still has value!
     

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