POST YOUR COLOSSAL SQUID QUESTIONS HERE

Discussion in 'Physiology and Biology' started by Steve O'Shea, Apr 16, 2008.

  1. Steve O'Shea

    Steve O'Shea Colossal Squid Supporter

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    We've set this thread up for you to post any questions that you may have about the Colossal Squid here.

    Please remember that it will be rather difficult for us to respond as quickly as we would like to between the dates of 26 April and 03 May, but we will do our very best to attend to them as and when we can. The www.TONMO.com community is large, with many experienced folk online, so we are sure that you will receive the expert advice that you want.

    Us

    edit: The webcast is now online, available here

    [URL2="http://www.tonmo.com/community/index.php?threads/9228/"]Discuss with us[/URL2]. (note: discussion spans many pages)

    :squidaut:
     
  2. Tintenfisch

    Tintenfisch Architeuthis Staff Member Moderator

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  3. Jean

    Jean Colossal Squid Supporter

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    "squiz" has made it into the headlines!!!! :lol:
     
  4. Octodude

    Octodude Blue Ring Registered

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    Well, here's one: Why is the collossal squid (seems to be anyway) so radically different, morphologically, than the giant squid? The fins, mantle, and "head" all seem so to represent a creature that sits and waits, rather than jetting around. The claws could hint at this as well, for grabbing prey and making sure the squid doesnt have to wait for food to wander by again.

    I am an amateur to this still, but I am curious.
     
  5. Jean

    Jean Colossal Squid Supporter

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    I've always thought of Messie as a fairly active hunter! That mantle is quite heavily muscled and I would think it can move very quickly when it chooses to. I've always pictured it cruisin' until it saw potential (large) prey, then a flurry of activity which would see dinner secured by the claws and then chomped down.

    J
     
  6. daviddickinson

    daviddickinson Blue Ring Registered

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    Size

    I think I read that one of the first things you will want to determine is the sex of the animal - do you think if this is a female then it is close to the maximum size and if it turns out to be a boy, how much bigger do you think the female could be? I just also wondered what techniques you might use to help determine the potential size for the species?
     
  7. octobot

    octobot Robotic Staff Staff Member Robotic Staff

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  8. monty

    monty Colossal Squid Staff Member Supporter

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    I can give a half-baked answer that the sex difference in size will probably be approximated by comparing it to other squid species. This may be a bit tricky, because Mesonychoteuthis is a cranchiid squid, and so it's not that closely related to other large squids. I don't know what the typical size difference is in the cranchiids, but I'm sure that's being taken into account.

    The most direct way to estimate the max size, though, will be from beak measurements. Steve's lab has a collection of a whole lot of beaks collected from toothed whale stomachs, and have carefully been measuring the size of the beaks for years. So if one imagines that the beak grows at the same rate as the squid, you can scale the squid to the size of the largest beak they've found. They already did that with the immature 2003 animal, but with this one, they'll start to improve the guesswork on that: it's possible the animal keeps growing after the beak stops growing, or vice-versa, for example. Or just that the squid grows proportionally faster than its beak, or the beak than the squid.

    In any case, I'm sure precise measurement of the beak is a priority for Steve & crew to relate it to their wealth of data in this department.
     
  9. Jean

    Jean Colossal Squid Supporter

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    Yes there will be a relationship of beak rostral (see pic) length to body (usually dorsal mantle) length and weight........however, to create the regression equations you usually need many examples of known size (I used 1100 for N. sloanii). By measuring those beaks and lengths etc you can use Excel or similar to plot beak length against body weight/length and thus calculate an equation. I doubt Steve & Co will be able to do that as they just don't have the available specimens and these relationships are quite species specific. Steve's beak collection won't work because they don't have the size of the original squid eaten by the whale.

    J
     

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  10. Tintenfisch

    Tintenfisch Architeuthis Staff Member Moderator

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    As Jean said, it's actually the giant squid we believe to be more the sit-and-wait type (very small fins, relatively weak mantle musculature, body not strongly attached to mantle - all things that would be problematic for prolonged, fast swimming), while the colossal appears to be a very active swimmer (extremely large fins, very thick, muscular mantle, head fused to the mantle as in all cranchiids).

    The giant and colossal squids are in different families (Architeuthidae and Cranchiidae respectively); each family is a group of genera that have certain morphological traits in common, so some of the differences are 'because' they're in different families (or, you could say they're in different families because of some of the differences), e.g. the means by which the head is attached to the mantle. Within the families there can also be a wide range of morphologies - different relative fin-size or arm-length for example. Have a look at some of the cranchiids at the link above - even the eyes vary a lot (and some are very strange.) The cranchiids are morphologically quite diverse, so Mesonychoteuthis has some big (ha ha) differences even from other genera in the same family. With Architeuthis, it's hard to say what variations there could be within the family, because at present (according to genetics at least), there is only one genus and species worldwide, Architeuthis dux.

    Hope this helps.

    :smile:
     
  11. Jean

    Jean Colossal Squid Supporter

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    Love the C. scabra pic in the puff ball shape :grin:
     
  12. monty

    monty Colossal Squid Staff Member Supporter

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    Sure, but you've gotta admit, two data points works a lot better than one data point: at least then you can judge whether drawing a line of slope beak/mantle from the 2003 animal matches up with beak/mantle for the new one, and if it does then have a bit of confidence about guessing the mantle size from the biggest beak...
     
  13. Clem

    Clem Architeuthis Supporter Registered

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    An appeal for questions? Ahhh. This I can do.

    1. If the eyes are reasonably intact, I'd be curious to know if Meso, like other cranchiid squid, has eyes that are open to seawater.

    2. Does the musculature of the arms terminate at the head, or does it extend all the way to the posterior of the squid's head? To visualize what I'm talking about, flex your fingers up on one hand so that the tendons on the back of the palm stand out. Fingers are arms, palm is head, wrist is posterior of the brachial crown and tendons are (speculative!) muscles. (If you want to go all the way, hold a marble in the web between middle and ring fingers and call it an eye.) If the arm musculature does go all the way to the back of the head, as the tendons in your hand go back to the wrist, does each arm have its own tube of muscle through the head or is the musculature shared?

    3. If the internal photophore is present, does it appear large enough to be of any utility, or does it appear rather vestigial?

    Thanks. This is all very exciting. I'm on Tintenfisch. I mean tentacularhooks. I mean tenterhooks.

    Clem
     
  14. monty

    monty Colossal Squid Staff Member Supporter

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    1. If it's not, it will call into question the whole taxonomy of squids... which would be fine with me :grin:

    2. I've been trying to research this sort of thing for my own nefarious purposes, and can say that it is extremely unlikely. Cephs don't really have any tendons at all, and for the most part they don't even rely on connective tissue for leverage; all their muscle action is based on the "muscular hydrostat" principles worked out by Kier. Certainly, there are no cephs that have anything like sheaths that have muscles that slide relative to adjacent muscles... except for the separate organs inside the mantle cavity, they're mostly big masses of muscle with a few non-muscle bits embedded in the muscle, but there's no parts that slide relative to each other...

    More than you could ever want to know (almost) can be found at http://www.bio.unc.edu/faculty/kier/lab/publications.html

    but Kier has a frustrating habit of describing the arms' and tentacles' cross section, but not what the geometry and innervation of the muscles is like as they merge together at the brachial crown. Why I see this is a frustrating omission is left as an exercise for the reader ( for now. :madsci: ) Particularly since the CAT scan data Steve & crew posted a few years ago doesn't show muscle fiber direction :banghead: )

    3. You mean the intraocular photophore many cranchiids have, right? Have you been reading here:
    http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=117163
    ?
     
  15. Clem

    Clem Architeuthis Supporter Registered

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    :alarm::alarm::alarm::alarm::alarm:

    Monty! No! Gaahhh! That's not what I was saying! I was merely using the appearance of tendons on the back of a human hand to illustrate my (speculative!) musings on the arm musculature, and how those muscles might extend from the buccal plane all the way to the back of the brachial crown, not unlike the configuration of a bullpup rifle. I've attached a pic to show where this notion came from. I've outlined in green the arms IV pair. Now, perhaps it's an accident of debriding and abuse from longliners, but it certainly appears that both arms IV share a connection to a single distinct muscular structure that terminates at the posterior of the brachial crown. My purposes aren't nefarious, but if all the arms are so anchored, I wonder how their actions would impact the eyes, which appear to be nestled between the muscular bases of arms II and III, and what advantage, if any, would be conferred on an animal that could squeeze with its arms and its head.

    Now I'll go read those things you linked to.

    Clem
     

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  16. Jean

    Jean Colossal Squid Supporter

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    welllllll marginally, problem is, that often the relationship is not linear, it may be a power curve or some other (mine is a ln relationship)!

    j
     
  17. monty

    monty Colossal Squid Staff Member Supporter

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    That's sort of why I said 2 points is a lot better than one point. It's really sort of more than 2 points, because you have (size of 2003) and (size of new) and (beak of 2003) and (beak of new) so you can either plot how the ratio changes as a function of size, in some very limited way, or test if it's also a log relationship by trying it with (log size)/beak or size/(log beak) or (log size)/(log beak), but it could easily be some wacky curve, and having 2 points lets you fit things a bit better than 1. Of course, 3, 10, 100, or 1000 points is a lot better, though... I just think the guess of the size of the one that left the biggest beak starts to get a lot less wild with 2 data points than one, is all...
     
  18. monty

    monty Colossal Squid Staff Member Supporter

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    I didn't mean to suggest you thought they had tendons... but I did want to clarify that for other people. I'm starting to get more of what you're saying, though. The hard part is that the arms and the head are mostly muscle, so in some ways where the "arm muscles" end and the "head muscles" start is sort of arbitrary. They don't seem to like to deform their heads as much as their arms, obviously, so I'd think that any extension of arm musculature into the head is primarily to anchor the bases of the arms. I'd expect there to be some sort of support muscles around the brachial crown all the way back, so I'm pretty sure that the head can't be thought of as a bundle of arm muscles held together by connective tissue... but there might well be some arm-muscle-bits mixed in going back quite a distance.

    It's also, of course, quite possible that I'm just confused. I've tried to figure this out from diagrams and histology slides for a while, but I haven't seen it well-documented anywhere. JZ Young published some amazing books of histology, but they focus almost entirely on the neuroanatomy, so they don't really address this... in Nixon & Young, in fact, Kier is the only one referenced for arm musculature, except as related to suckers, at least for the loliginid overview (yeah, I know Mesonychoteuthis isn't a loliginid). I've got some xeroxes of JZ Young histology stuff, particularly The Anatomy and Nervous System of Octopus vulgaris, that shows this area in regards to the interbrachial commissure, that's the cross-connection between the nerves going down each arm. There's a 1908 monograph by Joseph Guérin that shows a bit just as the arms enter the brachial crown, that (insofar as my rusty French comprehends) shows that the basic arm muscle profile extends into the head a bit, and then there are some cross-connecting muscles that give some support. He doesn't discuss the eyes at all, though, and neither follows the arms back into the head. It seems, though, that the extension of the arms that go back to form the head are mostly anchors for the arms that are held pretty rigid.

    I did find that Nixon & Young show some relevant stuff, but it varies a lot between species, and even among cranchiids... I'll scan some pics and report back.
     
  19. Jean

    Jean Colossal Squid Supporter

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    it's just not that easy unfortunately, here's a fake regression (cos I don't have any real Messie data) and all it tells you is that one is bigger than the other! the pedantic scientist in me just won't allow for any meaningful conclusions to be drawn from this. And you can play with it all you want but you can't predict or draw conclusions from what simply isn't there. What happens in the younger/smaller sizes? Is there an ontogenetic change in growth form, do the older ones reach an asymptote (rare in squid but........), does the growth speed up/slow down?????? and so on, it's very dangerous to extrapolate based on only two sets of measurements!

    Argumentatively yours

    J
     

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  20. monty

    monty Colossal Squid Staff Member Supporter

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    "Oh, this is abuse. Arguments are down the hall." - Monty (Python):tongue:

    Are you arguing that having 2 data points is just as bad as having one? I didn't mean to argue that it would allow a high-confidence guess, just that it's a big improvement over one... mostly, because you can at least estimate how wrong the 1 point approximation is. I entirely concede that it will be a lousy guestimate anyway... but I think we *can* say some fairly reasonable things, like ML is monotonically increasing with beak length, that they won't be wildly uncoupled, and so forth. And since we want one as a function of the other, we can get ML(b) and and an estimate of dML(b)/db for each squid, so there are (kinda) 4 measurements, the value and derivative at each squid's beak size. I think it's not too awful to imagine that both the ML(b) and dML/db are monotonic and kinda smooth over the range, so it's at least possible to fit a curve made of two terms of the Taylor series instead of one. Is this a good estimate? Meh, not really, unless you make a lot of assumptions, but I think they're not completely insane assumptions.

    So I put forth that the "best" assumption from one squid with ML=ML0 and b = b0 is:

    ML(b - b0) = ML0 + (ML0/b0)(b-b0)

    and with 2 squids, with the other having ML=ML1 > ML0 and b=b1 > b0

    ML(b - b0) = ML0 + (ML0/b0)(b-b0) +
    ((ML1/(2b1(b1-b0))) - (ML0/(2b0(b1-b0))))(b-b0)^2

    (unless I screwed up the algebra)
    which is "better" assuming all the usual Taylor approximation stuff applies.

    I did cheat a little, and assume that the line from (0,0) to (b,ML(b)) is a good enough approximation of the derivative, though, too.

    Note that "better" doesn't imply "particularly good" but I think the curve is monotonic and pretty smooth and otherwise well-behaved over this range.

    It is quite true that this makes some horribly naive assumptions, and whether to use naive assumptions to get an answer or to say "I refuse to endorse and answer that I know is naive so it's probably wrong" is sort of a judgment call... I wouldn't bet my reputation on it, but it's not completely unbelievable. You could possibly do better by assuming some other form rather than a Taylor polynomial, like whatever the log relationship you found in Nototodarus looked like and trying to fit different constants to that, and maybe using (ML1 - ML0) / (b1 - b0) as the derivative estimate for the bigger squid, and stuff like that, too. In fact, I should have done the latter, and as penance I re-solved it:

    ML(b - b0) = ML0 + (ML0/b0)(b-b0) +
    (((ML1-ML0)/(2(b1-b0)^2)) - (ML0/(2b0(b1-b0))))(b-b0)^2

    Of course, this is, in some sense, all completely :tomato: rather than :grad: but people use these sorts of naive models for things all the time. And they sometimes kinda get the right answer, approximately.

    And it's not like there are dire consequences for guessing wrong :sink:

    p.s. I realized as I was going to sleep that I forgot to correct the ML(b1) value in the 1st deriv equation, on the unlikely chance that anyone is referring to this for some real reason.
     

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