Friday, July 30, 2010

Cephalopod Photography: Klaus Stiefel

Next on my (long and growing) list of cephalopod photographers to feature here is Klaus M. Stiefel, a neurobiologist who currently works in Okinawa.  All of the photos in this post were taken by him.  He was cool enough to release them under a creative commons license, so feel free to use them, just don't use them for anything commercial and make sure to give him credit (lots and lots of it.)  You can click through on all of the photos to access them on Flickr, including larger versions (which I always recommend - they make great desktop wallpapers.)  Let's dive right in, shall we?

To start off, a portrait of an adorable cuttlefish of unknown species (if anybody can tell, please post it in the comments - I'm embarrassed to admit it, but I'm very bad at identifying species):

Cuttlefish face

Moving right along, we have these two lovely photos of the flamboyant cuttlefish, Metasepia pfefferi.  Klaus calls this posture a "threat display", although I'm pretty sure it is used both as a defensive behavior and during hunting, especially for shrimp and prawns.  My favorite thing about pictures of M. pfefferi is that they always look so relaxed, just because of the shape of their pupils.

Flamboyant Cuttlefish IV

Flamboyant Cuttlefish III

Last in our illustrious lineup of cuttlefish is an unidentified individual who is expressing its papillae beautifully and showing off its ability to use binocular vision by looking at the camera with (count 'em) two eyes.

Sepia in the Keramas I

You want squid?  We've got squid!  Well, a squid.  This is a juvenile squid (species unknown, though one of the commenters on Flickr suggests that it's a bigfin reef squid, Sepioteuthis lessoniana) floating among the fronds of a sea lily.

Bobtail Squid

Here is an octopus (again, species unknown) expressing a very striking white ring around its eye.  This looks to me like it might be related to the eye-bar body pattern component, which is used during defensive behavior by adult octopuses to obscure the shape of the eye or make it appear larger than it really is.


Here's a great shot of some octopus arm suckers, showing various degrees of flexion of the suckers themselves.  I wish I knew the species of octopus that these belonged to.

Octopus arm's suckers

I just love pictures of octopuses peeking out of things!  Here is the obligatory inquisitive-octopus-eyes shot:


In this series of photos, Klaus captured a dramatic color change in an octopus.  It looks to me like the octopus tried to camouflage itself, then decided that wasn't going to work and began to hide under the rocks.

Octopus color change 1
Octopus color change 2
Octopus color change 3
Octopus color change 4
Octopus color change 5
Octopus color change 6
Octopus color change 6

 Finally, we'll close with a gorgeous photo of a cephalopod that is too often ignored: the Nautilus.


 Thanks for reading!

Cephalopod Photography: Lawrence Tulissi

I stumbled upon the Flickr group: Cephalopods , and decided that it was about time to put up some more eye candy on the site.  I've gotten in touch with some of the photographers whose cephalopod photos are in the group, and I'll be doing a series of posts with each post featuring the work of a single photographer. 

First on the list is Lawrence Tulissi. All of the photos in this post are click-through-able if you want a larger image - which I highly recommend - and are his property (so don't steal them.)

First is an octopus (looks like it could be O. cyanea to me, but I'm not the best at species identification) in a neat posture, with a very striking pattern of coloration.  This was taken at Truk Lagoon, which sounds like an incredible place to dive.

Chuuk 2010-090

This next one shows the suckers of a giant Pacific octopus.  I like that you can see suckers in various states of contraction, showing the great flexibility that having multiple sets of muscles in each sucker affords the octopus.


This next one is of O. briareus, the Caribbean reef octopus, showing off its long arms and exhibiting some great body patterning.  This posture is probably defensive, judging by how conspicuous its coloration is and the fact that the interbrachial web is spread.


This picture shows the eye of a giant Pacific octopus.  The description of the photo says that the octopus was in its den, and the closed pupil slit indicates that it was likely resting.  In a neat case of functional homology, octopuses, like many vertebrates, tend to close their eyes when they rest - it's just that, since they have no eyelids, they do this by closing their pupils.  If you don't believe me check out Brain and behavioural evidence for rest-activity cycles in Octopus vulgaris by Brown et al. (2006).


Moving on from octopuses (as much as it pains me), we'll finish up with two wonderful shots of Carribean reef squid, Sepioteuthis sepioidea:

Turks & Caicos 2010-005

Turks & Caicos 2010-039

Thanks for the photos, Lawrence!

Everybody else, thanks for reading.  I'll be writing on some brand-spanking-new research on the role of serotonin in the octopus learning system next week, so I'll see you then!

Tuesday, July 27, 2010

Pass the clams, please: A strategy for object retrieval in the octopus.

          I recently blogged about a line of research on octopus reaching movements, but I left out an important study for time's sake.  I promised to cover it promptly, and so I'm making good on that promise here.  To recap:

          It has been shown that reaching movements by octopuses are controlled by the nervous system of the arms relatively autonomously from the central nervous system; that is, a severed arm can complete these movements on its own, given the proper stimulation of the base of the nerve cord of the arm.  This is all well and good, as the movements being studied were rather simple, involving the extension of an arm.  This reaching movement was found to consist of a propagating wave of muscle activity down the arm, a solution to the control of such a flexible appendage that greatly reduces the amount of neural computation that is needed to make such a movement.)

          The study I'll look at today is Octopuses Use a Human-like Strategy to Control Precise Point-to-Point Arm Movements by Sumbre et al (2006).  In it, the authors study a more complicated movement: retrieval of an object using a single arm.  This is a problem of interest to neuroscientists and roboticists, because understanding how the octopus generates controlled, precise movement using an appendage with so many possible movements might give us some insight into the optimal solution of this problem.  This could help reveal general rules of efficiency in neural programming.

          Beginning (as is advisable) at the beginning, the authors videotaped reaching movements in O. vulgaris that were elicited by touching a piece of food to the animal's outstretched arm.  Their observations revealed that octopuses create joints in their arm during this movement, around which they move stiffened segments of the arm much the same way that animals with a skeleton (notably, humans) do.  A series of stills from one of their videos and a lovely diagram of the arm "joints" of an octopus who is about to eat an unhappy-looking fish are shown below:

          It turns out that most of the distance covered in this movement sequence comes from the arm's rotation about the medial joint (the yellow one), much as most of the effective range of human retrieval movements come from flexion of the elbow.  After some more detailed analysis of the kinetics of this movement (which I'll skip here - but please check out the paper if you're interested) the authors go on to probe the pattern of muscle activity that is responsible for this movement as they did in their earlier studies (for a brief explanation of their methods, see my earlier post; for a longer one, see the paper reference therein.)  They found differences in patterns of muscle activity depending upon where in the arm recordings were being made.  When they looked proximally to the medial joint (eg. in arm segment L1 in the above diagram,) they found that a wave of muscle activity propagated away from the body, as it does in reaching movements.  When they recorded from a portion of the arm distal to the medial joint (eg. in arm segment L2,) they found that muscle activity was propagating in the opposite direction - from the tip of the arm towards the base.

          Using these results, the authors offer an elegant explanation of the neural control of this behavior.  They suggest that the initiation of a retrieval movement involves the initiation of two waves of muscle activity, one starting from the tip of the arm and one from the base.  Where these waves meet, the medial joint is formed.  In this way, the octopus nervous system simplifies the problem of finding an efficient way to retrieve an object, a problem which would be hard to solve on the basis of proprioception or neural control contingent on a direct representation of sensory space due to the flexibility of the octopus's body.

          In case you were wondering (I sure was), an experiment that was reported in the supplementary material (though it seems pretty important to me) revealed that retrieval could not be elicited in denervated arms in the way that arm extension can.  Therefore, it appears that some input from the central nervous system is required to initiate this more complicated movement, although it is still possible (and seems likely) that, once initiated, the movement is driven primarily by peripheral mechanisms local to the arm performing the movement.  The authors found that ablation of the anterior basal lobe left octopuses unable to initiate object retrieval, confirming its suspected function as a motor center in the octopus.

          The authors finally put forth a hypothesis of convergent evolution of reaching movements between octopods and vertebrates:

                    It is especially surprising that of all possible
                    geometrical structures and motor control strategies
                    with which a flexible arm can bring an object to the
                    mouth, the octopus generates a quasi-articulated structure
                    with a striking morphological and kinematic resemblance
                    to the multijoint articulated limbs of vertebrates.
                    Because the hypothetical common ancestor of cephalopods
                    and vertebrates dates back to the beginning of
                    Cambrian era (about 540 million years ago), fetching
                    appears to be a genuine and rare case of evolutionary
                    functional convergence, where two independent attributes
                    (morphology and neural control) coevolved to
                    achieve a common goal.

          I have no particular problem with this hypothesis.  I'd be interested to see if these types of movements are present in other species of cephalopods, both decapods and other octopod varieties.  I think that the case for convergent evolution in this instance will always be a hard sell, because (unlike, for example, the eye) the anatomy of the body parts executing the movement in question are so different.  In addition, the movements studied in this paper were elicited in very specific conditions using octopuses that were trained to extend their arms and wait for food to be pressed to them, leaving it unclear what other types of movements they might make in retrieving an object as well as the relative importance of the aforementioned quasi-articulated arm movements in the ethogram of the octopus.  Those criticisms aside, I'm willing to accept the idea that articulated movement really does represent a good solution to the problem of controlling movement, because it shows up across animalia so often and in so many forms.  Why wouldn't we expect the octopus to get in on the action?

          Thanks for reading!
Sumbre, G., Fiorito, G., Flash, T., & Hochner, B. (2006). Octopuses Use a Human-like Strategy to Control Precise Point-to-Point Arm Movements Current Biology, 16 (8), 767-772 DOI: 10.1016/j.cub.2006.02.069

Do octopuses play?

         I was recently pointed to this article on "octopus intelligence".  I like the article (which features quotes from such cephalopod research all-stars as Roger Hanlon and Jennifer Mather,) although I am a bit let down by the brief, incomplete explanation that is given to the various "intellectual" abilities of the octopus such as "problem solving" and "play".  Both of these behaviors are difficult to define precisely, and are often understood in vertebrates by analogy to human experience.  For example, one of the criteria that is used to define play in animals (as stated in Kuba et al. 2003, a study on play-like behavior in octopuses) is that it is "spontaneous and pleasurable ('done for its own sake')".  This is one of the central features of play - that it appears to serve no other immediate purpose than to entertain or occupy the animal expressing the behavior.  I take some issue with the use of the term "play
 to describe octopus behavior, at the very least because the implications of play-like behavior in the octopus are not very well studied yet.  It's much harder to determine the motivational significance of an activity in an octopus than it is in, say, a rat.  This is because we know the brain and behavior of the rat much more thoroughly than we know those of octopuses, and since they are structurally similar to ours we can relatively easily design valid measures of motivation in rats.  In contrast to the vast (though still incomplete) neurological and behavioral description of pleasurable and aversive states in the rat that we have generated, we have only a very crude measure of the possible hedonic characteristics of an activity in the octopus; that is, we can assume that the octopus will do "pleasurable" things and will avoid aversive things, but we have little more to go on when we are talking about the motivation of an octopus.  Because of this limitation, I think that it may be too early to say for sure what processes play-like behaviors in the octopus actually represent, and so the touting of play as evidence of the impressive mental powers of the octopus also seems premature.

         Whoa, now!  Before I go making assertions like this, I should look at the research, right?  Good call.  Let's see what the vast scientific library that is the internet can teach us about the play-like behavior of octopuses.

         I'll focus on Kuba et al. (2006), a recent study that was done to examine putative play behavior in O. vulgaris.  In this study, the authors exposed octopuses to stimuli made out of Lego blocks for half an hour at a time repeatedly over a period of 7 days and scored the octopuses reactions to the objects.  The authors' scoring system is illustrated below (this if Figure 1 from the paper.)

         As you can see, level 3 (which the authors describe as "play-like") and level 4 (which the authors call "play") involve repeatedly manipulating non-food objects in complex, non-stereotyped ways for a significant amount of time.  Out of 14 (wild-caught) subjects, object manipulation that was scored at level 3 was observed in 9 subjects, and object manipulation that was scored at level 4 was observed in one subject.  There was no difference of age or hunger state in this behavior (young and old octopuses showed the same sorts of behavior, as did hungry and sated octopuses.)  Play-like behaviors tended to occur after several days of presentation of the stimulus, suggesting that this was not merely exploratory behavior, which appeared to decrease during the first few days of exposure (as the octopuses presumably got used to the presence of the stimuli in their tanks.)

         By this point, I tentatively buy the characterization of these behaviors as "play" - they don't appear to serve any purpose for the octopus, who is clearly not simply confusing the objects with food.  They are exhibited after the octopus has presumably had ample time to learn that they do not represent a threat.  The behaviors do not appear to clearly belong to any other class of behavior (except perhaps tactile exploratory behavior.)  As I said before, however, using the existence of these behaviors to argue for the intelligence of the octopus seems premature to me.  For one, the significance of these behaviors in the wild is not well understood - they must confer some survival utility, but they do not appear to be disproportionately expressed in young, rapidly developing octopuses as they are in mammalian young, and so are unlikely to contribute to neurodevelopment in the same way that play in mammals (especially social mammals) is thought to.  We know that play in social mammals (like humans, some apes, and rats) serves a variety of functions in development - to establish dominance hierarchies, to develop skills for living within social organizations, to learn hunting and food-gathering behaviors, to help develop motor coordination, etc.  We have comparatively little sense of the importance of play in the life of an octopus, and so it is hard to know what play-like behavior means in the context of octopus cognition.

         Because we know that play is very important to the cognitive function of mammals I mentioned previously (more properly, we know that disrupting play behavior causes deficits in behaviors that depend on play to develop,) we can claim that play is part of a group of behaviors that make manifest the intelligence of these animals.  Without knowing what play-like behavior does for an octopus, it's hard to say whether it implies an analogous intelligence in these animals.  It might be explained in many cases as a simple extension of exploratory behavior.  As a foraging predator, it makes sense that O. vulgaris would be served well by repeated, thorough explorations of the same object, which mobile and semi-mobile prey would presumably periodically be found on.  This behavior might be explained as part of a foraging strategy that is somewhat impervious to associative learning, and so violate the criteria that we use to classify a behavior as play all together.

         My discussion thus far has accepted the hypothesis that behavior classifiable as play occurs regularly in the octopus, and thus needs to be explained in terms of its adaptive utility to the animal.  Based on the previously summarized paper, however, clear play-like behavior in the octopus appears to be pretty rare.  On the 5th day of the experiment, when play-like behavior peaked, 444 interactions with the stimuli were observed.  Out of these, 13% qualified as level 2 (they involved manipulation beyond very basic exploration of the object with the arms,) 0.9% were scored as play-like, and a single observation (0.02% of the total observations) was scored as being definitively "play".  I think this was a well-designed study, but the results don't convince me that play (as defined by the authors) is terribly important in the lives of octopuses, and might just as well represent a rare, specific type of interaction that they have with unusual stimuli in a laboratory environment.

         I realize that I have been sort of hard on this study.  I don't want to imply that octopuses are not remarkable animals that are capable of many things one wouldn't expect from a mollusc.  I do think, however, that it pays to be very skeptical about the use of the terms "play" and "intelligence".  Both of these are concepts that we understand primarily by analogy to our experience of them as humans.  We know that social play in vertebrates is indeed play (even the scientists among us) because we know what a play fight feels like, and understand intuitively how it differs from a real fight.  We can extend this to behaviors that we see in animals (with more or less accuracy, depending on the situation.)  We know what intelligence means (or we think we do) because we have expectations of how people should function, and we can draw analogies to other vertebrates who have the same sort of behavioral flexibility and environmental demands that we do.  One might dismiss this as unscientific, but we have pretty good evidence that the neural structures that are responsible for a variety of emotions and types of behaviors are conserved in some form across species (in mammals at least.)   Thus, we can be somewhat comfortable in our understanding of the role of play in a rat's cognitive life because, at a pretty complex level of structure and function, they have essentially the same machinery in their head that we do.  It's a bit less convincing to use the same anthropomorphic logic to justify associating what looks like play behavior in an octopus with the "intelligence" that we suspect goes along with play behavior in vertebrates.  This is because the existence of analogous neural substrates and their accompanying cognitive functions (emotions, hedonic value, etc.) is not clear.  It strikes me as somewhat mistaken that we would use psychological constructs that were created to describe human behavior such as "play" and "problem-solving" to describe cephalopod behavior, though we do it even when they appear to be a poor fit to the behavior in question.

         As Jennifer Mather points out in her quote in the Boston Globe article: “We’re smart and the octopus is smart, but octopus intelligence just can’t be related to our intelligence.”  This I have to agree with.  Just because we can call a behavior something that sounds familiar (in this case, "play") doesn't mean that we've explained it, even though it might appear this way.  I think that octopuses are fascinating and astounding creatures that exhibit very interesting behaviors; I'm just not quite convinced that they play.

Thanks for reading!
Kuba, M., Byrne, R., Meisel, D., & Mather, J. (2006). When do octopuses play? Effects of repeated testing, object type, age, and food deprivation on object play in Octopus vulgaris. Journal of Comparative Psychology, 120 (3), 184-190 DOI: 10.1037/0735-7036.120.3.184

M Kuba, D V Meisel, R A Byrne, U Griebel, & J A Mather (2003). Looking at Play in Octopus Vulgaris Coleoid cephalopods through time, 163-169

Friday, July 23, 2010

Neuromuscular Dynamics of Octopus Arm Movements

I was planning on writing an article about cephalopod statocysts (and I still am; I've just had trouble deciding which pieces of research I want to cover and which I want to leave out) to continue on the theme of cephalopod sensory systems.  I've stumbled upon a line research that I just had to blog about, though, so I'm putting off the statocyst post even further.  The research in question is a series of studies by The Octopus Group at the Hebrew University of Jerusalem on the biomechanics and neural control of reaching movements of octopuses.  I read this research some months ago (before I was blogging,) and I was reminded of it while watching Twister (the resident E. dofleini at the Niagara Falls Aquarium) groping about in his enclosure.  I noticed that, as he moved his arms about, the movements almost always started with a bend near the base of the arm, which traveled out to the tip, becoming sharper and moving faster as it proceeded.  It looked for all the world like the way a wave travels through water (or, more geek-ily, the way one imagines spontaneous activity propagating in a spatially extended nervous system.)  The series of studies I will talk about here shows that this is generally the case, and characterizes the way that this happens with some detail, although we still do not know this system in nearly as fine detail as we know the vertebrate neuro-muscular system.  I'm getting ahead of myself, though.

Why do we care about the details of how octopuses move their arms?  First, it's just plain cool - who, upon looking at an octopus moving, hasn't wondered how it can possibly keep track of all those arms?  Second, the octopus arm provides a unique model nervous system for a few reasons.  It is a muscular hydrostat - that it, having no bones, it is a system of muscles that run perpendicularly to each other that maintain a roughly constant total volume; this property of an octopus arm allows it to function like a very flexible vertebrate limb because the muscles can pull against each other to form temporary, semi-rigid structures that allow the arms to bear weight.  As such, it is a novel motor system (in terms of research, that is,) with most of the well-characterized motor systems we know of (ie. human, primate, reptile, etc.) are composed of skeletal muscles, which pull against bones.  Besides this, the task of coordinating the movement of eight almost infinitely flexible arms is a herculean task in terms of neural processing, and it would be very informative (as well as a triumph of systems neuroscience) to understand how this is done.  It has been thought, since the early days of octopus neuroanatomy, that much of the movement of the octopus's arms (and probably those of other cephalopods) is encoded in the nervous system of the arms rather than in the central nervous system (Graziadei, 1971).  This is evidenced by the fact that there is no straightforward representation of the arms in the brain of the octopus, as there is in humans and most other vertebrates, as far as we know, and so it is unlikely that fine motor control comes from the central nervous system.  Supporting the importance of the distributed nervous system of the arms is its incredible scale: the nervous system of the arms is much larger than the central nervous system of octopus, containing around 2/3 of all of the neurons in the animal.  The octopus arm, then, is a unique example of a highly complex, distributed motor system that stands in contrast to the centrally controlled motor systems we are most familiar with.  As with almost every topic in comparative neuroscience (I'm a big sucker for it), I think that the octopus motor system is important because by understanding it, we will understand more about vertebrate nervous systems; that is, we will (pretending for a moment that we could actually solve both systems) understand which features of them are critically related to the specifics of vertebrate and invertebrate neural functioning, physiology, development, and ecology.  We would come closer to understanding why each system evolved the way it evolved.  Finally, we would exercise our tools of modeling neural computation in a way that would allow us to figure out how generalizable they are.  My final verdict: this is a good thing to study.

So now you're bored.  You want to hear about some research!  Well, I won't disappoint; at least, I hope I won't.  We'll start with Gutfreund et al. (1998), one of the early papers out of this research group, which kicked off this line of research by examining the neuromuscular dynamics of octopus reaching movements.  I should note that (presumably for simplicity,) this group generally only studies reaching movements in a single arm - it is not know exactly how their findings might relate to more complicated movements, including those involving multiple arms.  As a disclaimer I am going to leave out description of a large portion of their study, which I encourage you to read in full, for my own convenience, and only present the results that I think are most relevant to the topic at hand.

This authors in this study used electromyography (a method of measuring the electrical activity of muscles) in O. vulgaris to determine how arm muscles are activated in sequence to produce octopus reaching movements.  Briefly, they put electrodes through two points in a single arm of their (anesthetized) test animals, then allowed the animals to wake up and elicited reaching movements by tempting the octopus with either a crab or a target that was associated with food.  They videotaped the reaching movement, which allowed them to compare the electromyogram to the behavior of the octopus.  Reproduced below is their first figure, showing the gross cross-sectional anatomy of the octopus arm, as well as their electrode placement:

The white arrows indicate the position of the electrode, which is the white line running through the muscle.  The striated outer portions of the arm are the muscle, and the round shape in the middle is the nerve cord of the arm.

They found that reaching arm movements usually start with a sharp bend near the base of the arm, which travels outwards until it reaches the tip, accelerating somewhat throughout the extention and then slowing as the arm reaches its target.  Here's a series of images showing the behavior:

The authors found that this type of arm extension occurs virtue of a propagating wave of muscle contraction traveling down the arm, from the base to the tip.  Shown here are examples of the type of data they used to confirm this:

The left panel shows two electromyograms from a single trial, the top one from the electrode nearer to the arm tip, and the bottom one nearer to the base of the arm.  The arrows indicate when the bend in the arm reached each electrode.  As is apparent, neuromuscular activity at the proximal site started earlier than that at the distal site, coinciding approximately with the timing of the movement of the bend in the octopuses arm.  The graph shows the correlation between the lag in the electromyogram record between the two sites and the time it took for the bend in the arm to move between the two sites.  It's clear that the propagation of the wave of electrical activity down the arm is highly correlated with the motion of the arm.  The authors continue on to characterize some of the properties of these arm movements in more detail and propose a mathematical model for the movement of the octopus arm, but I'll leave those results out, here.  I recommend this article for it's methodological clarity - too seldom do authors take such pains to make their method so clear and so thoroughly address their research question.

Moving on, the same reearch group (with a different first author) published a paper in Science describing their experiments with isolated arm preparations (Sumbre et al. 2001).  This is where it gets really interesting to me, because this experiment really gets at the distinction between central and peripheral motor control.  The authors made their preparations by either denervating one arm of an octopus that had already been decerebrated (a procedure somewhat akin to an octopus lobotomy) by severing its connection to the brain, or by severing an arm completely.  They then attached the base of the arm to a surface, and stimulated the nerve cord at the base of the arm.  It was found that, in a large percentage of cases (46%, to be exact,) the movement resembled the reaching movement seen in an intact animal.  The figure below (taken from the paper) shows the reaching movement of a normal animal (on the left) and that elicited by stimulating the nerve cord of a denervated arm in a decerebrate animal:

Importantly (for reasons I'll explain in a second,) it appears that the arm movements were initiated, but not sustained by the stimulation.  We can tell the difference because the "reaching" movement continued through to completion even when it began slightly after the experimenters stopped stimulating the arm.  This shows that the brief stimulation started a motor process that was maintained by the intrinsic neuromuscular system of the arm.  The authors also found that similar movements could be elicited in amputated arms by "tactile stimulation of the skin or suckers."  After a brief analysis of the kinetics of the evoked movements, the authors conclude that they, like those of intact animals, are caused by a propagation of muscle activity down the arm.

The authors' conclusion:

          "The division between the central and
          peripheral levels of the octopus motor control
          system resembles the hierarchical organization
          of motor control systems in other
          invertebrates and vertebrates, even
          though in the octopus it uniquely serves as
          an important component in a goal-directed
          voluntary movement rather than in rhythmical
          or reflexive behaviors."

The peripheral nervous system of the octopus appears to play a much greater role in the programming of movement that does the peripheral nervous system of vertebrates (which can only independently control simple reflexes and some other involuntary movements like peristalsis), even to the extent that it can execute complex movements (like reaching as if to grasp) all by itself.  That propagating wave of muscle activity isn't coordinated by the central nervous system, like coordinated movements are in humans; rather, it's coordinated by the nervous system intrinsic to each arm.  This is convenient for the octopus because it means that it generally does not need to keep track of its arms (that is, it's central nervous system doesn't have to spend a lot of resources monitoring and controlling them) because they largely take care of themselves.  It's a good solution to the problem of having a large number of incredibly flexible appendages.

The exact extent of the arm's abilities to coordinate their own motor activity, as well as activity between arms, remains to be uncovered by more and more detailed experiments on a variety of types of movement, but the general conclusion seems pretty solid to me, and fits nicely with what we know about the neuroanatomy of the octopus.  It would also be interesting to see the results of similar studies in other cephalopods.  I have a sneaking suspicion that one could relate the extent of the peripheral nervous system's "motor autonomy" from the central nervous system to the complexity of arm movement required by a given species' lifestyle.  It would be a neat idea to explore (if I had a laboratory on the Italian coast and a million-dollar grant to study squids.  I can dream, right?)

There's one more article I wanted to cover here, but I don't have time at the moment, and I want to get this up tonight.  It's by the same group, and it applies what the previous studies showed to explain the way that octopuses retract their arms after they have grasped their target.  Hopefully I'll have a shorter post on that before the end of the weekend.

As always, thanks for reading!
Sumbre, G. (2001). Control of Octopus Arm Extension by a Peripheral Motor Program Science, 293 (5536), 1845-1848 DOI: 10.1126/science.1060976

Gutfreund Y, Flash T, Fiorito G, & Hochner B (1998). Patterns of arm muscle activation involved in octopus reaching movements. The Journal of neuroscience : the official journal of the Society for Neuroscience, 18 (15), 5976-87 PMID: 9671683

Graziadei, P.P.C. (1971). The nervous system of the arms. pp. 44-61 in Young, J.Z. The Anatomy of the Nervous System of Octopus vulgaris. Oxford : Clarendon Press.

Wednesday, July 21, 2010

So, enough about me...

I've been writing this blog for about 3 months, and it has been an immensely rewarding experience.  I've learned a great deal about all sorts of topics, had a chance to develop my writing skills, and enjoyed the virtual company of many wonderful science bloggers (almost all of whom are far more qualified than I, and whom I am very grateful to be able to observe and learn from.)

I assume that I've developed a small regular readership, as my traffic-tracking service indicates that I have between 5 and 20 returning visitors each day (depending on how recently I've posted.)  I figured I'd take this opportunity (as sleep doesn't seem to be working out for me, at the moment) to probe your minds for a minute, both to satisfy my own curiosity and to help me figure out how I should be running this thing.  If you have a second, please leave your responses to these questions in the comments:

Who are you?  Why do you read this blog?  What do I do right as a blogger, and what do I do wrong?

Thanks in advance for your help!

I'd also like to use this post to offer to trade articles with anybody who might be interested.  I'd love to have some guest posts on here.  I'd also like to try my hand at writing about something besides cephalopods (I have lots of other interests, I promise!), but I am not ready to maintain more than one blog at the moment, and I've decided to keep Cephalove firmly on topic.  Send me an email or leave me a comment if you're interested.

Tuesday, July 20, 2010

Links: 3rd Edition

It's time for some links!  I'm working on some posts about cephalopod statocysts (to continue my coverage of sensory systems,) but in the mean time, here's what's going on (cephalopod-wise, mostly) on the web.  There are some really funny news items this week.

An article at Deep Sea News makes the argument that Paul the octopus is actually psychic; at least as far as we can tell by current statistical standards.

Speaking of our friend Paul, he has officially reached internet stardom:  Parry Gripp has written a song about him.

Another brand-spanking-new article from the same site addresses the possibility that pharmaceutical waste can alter marine ecosystems.

I recently lam-blasted the way popular media talks about the Humboldt squid.  Over at Thoughtomics, this article exposes another sciency media frenzy for what it is: crap.

A burglar in Reno, Nevada decided to mess with his victims in a very creative way:  by microwaving a squid.  Seriously.

A new Syfy channel original movie, Sharktopus, gives us a vivid picture of what life would be like if half-shark, half-octopod monsters roamed the sea.  And I though Lifetime movies were bad...

Apparently, email spammers are trying to sell people squid now.  Does this mean that Viagra and pornography are no longer profitable?  Let's hope that this ushers in a new, more creative era of spam marketing.

North Korea has started leasing squid fishing rights to China.  The arrangement brings income to North Korea and supplies the strapped squid market in China.  I find fishery management interesting, if only because it's so critical to ocean ecology.

Finally, this UK man is charged for possessing squid pornography (and child pornography, but that's not interesting enough for a tabloid headline.)  It's apparently a criminal offense in the UK to have photos of somebody having sex with a dead squid.  My favorite line of this story: "Prosecuters amended the charge when it was admitted it could have been an octopus in the picture."  Oh, it was an octopus?  That's a different story.

I wish I could make this stuff up.

The Myth of the Humboldt Squid

I recently got a request (thanks to arvindpillai at Fins to Feet) to do a post on the shoaling and predatory behavior of Humboldt squid, Dosidicus gigas (also known as the Jumbo squid, and by those who don't know any better, the giant squid.)  I decided that this would be a good thing to do, because I hadn't read much about the predatory behavior of D. gigas.  So I spent a week searching the literature for scientific studies on Humboldt squid predatory behavior, and guess what?  I still haven't read much about it!

It turns out that there is very little known about the behavior of these squid.  The paucity of our ethological knowledge of them is shocking to me, given the disproportionate attention to this species in popular media.  I've seen at least one budding cephalopod enthusiast become intrigued by stories about this species to the extent of obsession, and it's not hard to see why.  Somehow, these squid have gained a reputation as fierce predators that are so bloodthirsty as to be regularly deadly to humans.  As such, popular TV shows and news magazines have run numerous stories about them, usually finding one or two divers who have (presumably) had experience with these squids (or at least heard stories about them) to expound on just how ferocious and aggressive they are.  Invariably, some sensational quip (that is almost always unsupported by scientific literature because, well, that literature does not exist) is used to drive home just how scary these squid are:

"It has probing arms and tooth-lined tentacles, a raptor-like beak and an insatiable craving for flesh -- any kind of flesh, even that of humans," says Pete Thomas in "Warning lights of the sea". 

Mike Bear, an otherwise anonymous diver from San Diego is quoted in this article as saying "I wouldn't go into the water with them for the same reason I wouldn't walk into a pride of lions on the Serengeti." 

“The Humboldt squid is a voracious predator that will eat anything it can get its tentacles on,” says Kelly Benoit-Bird, an oceanographer, quoted by Mark Floyd in this piece.

With all the hubbub, these guys must be pretty dangerous, right?  The stuff of nightmares, even!  I mean, just look at this bloodthirsty monster!

Oh wait, it's kind of cute, isn't it?

This is the myth of the Humboldt squid: that they are first and foremost dangerous, indiscriminate killing machines.  This is, frustratingly, the first (and often only) piece of information that is repeated about them in any given article.  But what's the real story?

Let's put this in perspective by considering the case of sharks, another predatory ocean-dweller that has been sensationalized as being imminently dangerous to humans (remember "Jaws"?  It was pretty silly, but a lot of people took that era's shark scares seriously.)  Fatal shark attacks on humans are documented somewhat regularly, and are discussed (albeit infrequently) in the scientific and medical literature (ie. this study on fatal shark attacks.)  I cannot find a single verifiable record of a fatal squid attack on a human in the medical literature (admittedly, I have only searched 3 online databases and Google scholar - I might be missing something.)  The closest thing I can find are fisherman's accounts in popular media of other fisherman's stories about hearing about people being killed by Humboldt squid.  Keeping in mind the D. gigas is a rather common animal, is fished for sport by casual fishermen, and is usually encountered in large groups (the commonly cited size is 1000-1200 animals per shoal, but I can't find anything peer reviewed to support this,) it looks like these squid are all but harmless, given how often it is encountered by lay-people and how few (if any) fatal encounters there have been.

This is not to say that I don't think it's possible that a Humboldt might kill a human someday; they are clearly aggressive, as several documented, non-fatal "attacks" on humans show.  I have to say, though, that the media attention that is payed to them (which is probably the reason why so many people are "interested" in them) is really a nuisance.  By making inflated claims about a species that we have little behavioral research about, media outlets encourage people to accept hearsay and horror stories as if they were biological fact.  These stories also draw attention away from other squid species whose behavior is very well characterized (ie. L. Pelalei) which might be better used to teach the public basic information about cephalopods.  Finally, by attempting to catch people's eye using gorey stories, such articles serve to blind people to really learning about these animals by focusing on how "bloodthirsty" and "horrifying" they are - an effect that can't be any good for conservation effforts.  I recognize that most people want an entertaining story rather than a dissertation out of their media, but this obvious bias in popular media coverage on this particular variety of cephalopods just bugs me because it is so pervasive and one-sided.

Now that I'm done ranting and raving, and have hopefully convinced you that D. gigas might not be the single-minded killers that they are often portrayed to be, I'll try to get at the facts (that is, our very limited scientific knowledge) of this species.  Most of the research that has been done on them has been about their interactions with predator and prey species and their movement through their habitat, rather than their ethology.  This is because they are an important species in the study of ocean ecology.  They can be caught regularly in relatively large numbers throughout their range with little risk of damaging populations - this is uncommon among large predators, which tend to be much more rare than those lower on the food chain.  They are also suitable to be tracked using remotely monitored tags (as per Markaida et al. 2005) which are difficult to attach to less robust cephalopod species.  As such, they are convenient and informative to study when trying to learn about how oceanic food chains work.

So, what do we know about their feeding habits?  For one, we know that, as Dr. Benoit-Bird was trying to point out, that Humboldts are active, generalist predators, eating (according to Nigmatullin et al.) all manner of prey including "cepepods, hyperiid amphipods, euphausiids, pelagic shrimps and red crabs... heteropod molluscs, squid, pelagic octopods and various fishes."  The authors also note that D. gigas is commonly cannibalistic, a facet of their predation that has probably contributed to their mythological status.  They are especially cannibalistic during squid jigging sessions, when they are excited by bright lights and surrounded by their injured conspecifics.  They feed near the surface mostly during the night, especially at dusk and dawn, and spend their days deeper in the water column (200-400m deep), as was shown by a radio tracking study by Gilly et al. in 2006.  They can vary their diet depending on changes in their environment, showing an adaptability that no doubt contributes to their great abundance (Markaid and Sosa-Nishizaki, 2002).  Interestingly, recent ecological research has shown that their range has recently expanded from its historical locus in the equatorial Pacific ocean off of Central and South America to extend to the Pacific Northwest (as described by Cosgrove and Sendal, 2005, Zeidberg and Robison, 2007, and Field et al., 2007), possibly due to their unique ability to deal with hypoxic conditions that other predatory species cannot.   The squid can retreat into deep water with very little oxygen in between daily trips to feed at the surface, and thus avoid predation by other species such as Mako sharks (Vetter et al, 2008)..  On an unrelated note, if I were a squid researcher named Zeidberg, I'd just go ahead and change it to "Zoidberg".  It's too perfect.

There is dissappointingly little to say about the shoaling and predatory behavior of D. gigas.  If there are any glaring omissions in my coverage of the topic, please let me know; however, I think I found most of what's in the scientific literature.  Basically, we know that they form large shoals, and that they are generalist predators.  More detailed information than that on the behavior of this species will have to wait for a new generation of adventurous ethologists.  Until then, I'll be turning back to those species of cephalopod about which we have enough information to draw useful conclusions about behavior.  Perhaps someday the sort of experiments that have been done in smaller, more easily handled species will be done in D. gigas, but until that happens, I will probably stay mostly silent about them in favor of covering studies on less glamorous species in detail.

Please excuse me if it seems like I've rained on the proverbial parade.  Excuse me also for not getting into the methods of the studies that I've cited.  I encourage you to peruse them, but I opted to cover a greater area of research superficially rather than getting in depth about any specific finding in this post, so that I could adequately sum up the state of scientific knowledge of the Humboldt squid.  To lighten the mood, I'll leave you with one more quote about the Humboldtl, by the realtively famous undersea cameraman, Scott Cassell, who has spent much of his professional career filming these squid (including a documentary titled "Humboldt: the Man-Eating Squid") and is quoted in this piece by Tim Zimmermann:  "They are one of the most beautiful creatures, and they just happen to be lethal... There is no life form on this planet more alien than a Humboldt squid."  I guess I didn't realize that any life form on this planet was "alien", given that they all evolved here.  Oh well - what do I know?

Thanks for reading!

ResearchBlogging.orgGilly, W., Markaida, U., Baxter, C., Block, B., Boustany, A., Zeidberg, L., Reisenbichler, K., Robison, B., Bazzino, G., & Salinas, C. (2006). Vertical and horizontal migrations by the jumbo squid Dosidicus gigas revealed by electronic tagging Marine Ecology Progress Series, 324, 1-17 DOI: 10.3354/meps324001


James A. Cosgrove, & Kelly A. Sendall (2005). First Records of Dosidicus gigas, the Humboldt Squid
in the Temperate North-eastern Pacific Archives of the British Columbia Royal Museum

Unai Markaida, Joshua J. C. Rosenthal, & William F. Gilly (2005). Tagging studies on the jumbo squid
(Dosidicus gigas) in the Gulf of California, Mexico Fisheriy Bulletin, 103, 219-226

Markaida, U., & Sosa-Nishizaki, O. (2003). Food and feeding habits of jumbo squid Dosidicus gigas (Cephalopoda: Ommastrephidae) from the Gulf of California, Mexico Journal of the Marine Biological Association of the UK, 83 (3), 507-522 DOI: 10.1017/S0025315403007434h

Nigmatullin, C. (2001). A review of the biology of the jumbo squid Dosidicus gigas (Cephalopoda: Ommastrephidae) Fisheries Research, 54 (1), 9-19 DOI: 10.1016/S0165-7836(01)00371-X


Zeidberg LD, & Robison BH (2007). Invasive range expansion by the Humboldt squid, Dosidicus gigas, in the eastern North Pacific. Proceedings of the National Academy of Sciences of the United States of America, 104 (31), 12948-50 PMID: 17646649

Byard RW, Gilbert JD, & Brown K (2000). Pathologic features of fatal shark attacks. The American journal of forensic medicine and pathology : official publication of the National Association of Medical Examiners, 21 (3), 225-9 PMID: 10990281

I know these citations are sloppy - for some reason, I'm having some trouble working with the ResearchBlogging citation generator.  I promise I'll fix it before next time.

Tuesday, July 13, 2010

Short and long-term memory in cephalopods

          I've heard the assertion that octopuses have short- and long-term memories several times in the past few days, mostly in discussions of the ethics of eating octopuses prompted by ethical questions raised about Paul, the famous German octopod.  It's interesting to me what these people don't say - that they think that having a multiphasic memory process makes octopuses worth not eating (because, well, people have multiphasic memories, and you wouldn't eat them, would you?!?  Sicko.)  While I don't think that memory capacity of an animal is associated in an uncomplicated way with its ability to suffer or its moral status, it seems to me like a nonetheless interesting question.  I'm almost sure that most of the people who use (read: copy and paste) this bit of information to support their beliefs have very little idea of what sort of research is behind it.  Let's face it: developing a working knowledge of behavioral research on cephalopods is something that just isn't on most of the public's mind.  In fact, until I began writing this blog, I had very little knowledge of the subject.  I plan to set the record straight, so that internet users need never make an unfounded or unqualified statement about memory processes in cephalopods again (a lofty goal, huh?)

          If you don't know octopus neuroanatomy very well (and who does?) you might want to check out the figures in this post.  I'll be talking about the vertical and superior frontal lobes of the octopus brain, and I know it sometimes helps to be able to visualize things like that when you're reading about them.  Just so that it's clear: the term "biphasic memory" means that the memory system in question has two discrete parts or processes (ie. short-term and long-term memory.)  A monophasic memory would have only one process, so that memories would last for a certain amount of time and then fade similarly in all circumstances.  A multiphasic memory system (which could be biphasic, triphasic, or more) is a general term to describe memory systems that are clearly more than monophasic, but are not completely characterized yet - and no memory system is.  Now, on to the research!

          J. Z. Young, that demigod of cephalopod neurobehavioral research, published one of the few papers I could find on this topic back in 1970, following up on his earlier work on the subject.  In it, he investigated the development of short and long term memory in O. vulgaris (I assume - he doesn't actually mention what species he uses in this paper, but he almost always used O. vulgaris) as well as the role of two brain areas in memory, the median superior frontal lobe (MSF) and the vertical lobe (VL).  To do so, he performed surgeries to remove one of these two areas of octopuses' brains and put them through a learning task.  In this task, octopuses were trained to either attack a rectangle (rewarded with a piece of fish) or withhold attacking a crab (which was punished with electric shock.)

          It turned out that octopuses whose vertical lobes had been removed were greatly impaired in learning to attack the rectangle.  Young explains this by claiming that the vertical lobe is involved in short-term memory, and that the acquisition of stable behavior day-to-day was impaired because the animals without vertical lobes could not remember events long enough for the training to be effective.  The animals without median superior frontal lobes, however, learned the task just fine, but were impaired in their long-term retention of it., suggesting that the MSF lobe might have some role in retaining learned information.  Interestingly, Young also found (in other experiments) that removing the vertical lobe after a task was learned resulted in a greater retention of the task.  These results suggest that the vertical lobe plays a role in the updating of memory stores, but is not absolutely essential for the recall of memories.

          His results from the attack-withholding task were less clear, but they suggest that animals with lesions, especially those with vertical lobe lesions, were less consistent than intact animals in learning not to attack a crab after being shocked each time they attacked it.

          Basically, Young argues (on the basis of this and some of his other experiments) that octopuses have a memory system that can be disrupted in more than one way; that is, it is possible to dissociate memory acquisition from long term retention, just like in vertebrates.  For the most part, more current research has agreed with his position, as we'll see in this next paper.

          Moving forward (past a lot of great research that I'll skip over for the sake of brevity) to 2008, Shomrat et al. used electrophysiological methods to test this hypothesis.  Before we get into their methods, let's look a bit more closely at the system that we are talking about (this figure is from Shomrat et al. (2008)):

          On the left is a sagittal slice of the supraoesophageal (over-the-oesophagus) mass of the octopus brain.  On the right is a diagram of the memory system in question.  Sensory information flows into the MSF from the arms and eyes before being sent along to the VL.  The VL neurons in turn send out information encoding attack.  It's been established that long-term potentiation (LTP) can occur in this area of the octopus brain, and this is a likely mechanism for the formation of memories in octopus (I blogged about this here - check it out if you need a little more background.)

          The authors' procedure went as so: O. vulgaris who had already been trained to attack a white ball either had their MSF tract cut (at the dashed line in each image,) severing the sensory input to the vertical lobe, or this tract was stimulated, causing LTP at the synapses indicated in the figure.  Shortly after the procedure, the animals were trained to avoid a red ball through electric shock.  It was found that animals with severed MSF tracts were slower than controls to learn to withhold attack, while animals in whom LTP was induced were quicker.  This is all well and good - it confirms what we already thought about the role of the vertical lobe in acquiring memories in the octopus.  The really important result from this paper came when the authors tested the octopuses a day later.  It was found that both MSF tract transection and LTP induction impaired recall after 24 hours.  So even though stimulation of the MSF tract improved short-term memory (presumably by hyper-activating the memory system in the vertical lobe,) it impaired long-term memory.  This suggests that these two processes are not identical; that is, that octopuses have discrete and dissociable short- and long-term memory circuits.  This general finding has been replicated in cuttlefish (see my post on cuttlefish memory) and nautiluses (Crook and Basil, 2008).

          Unfortunately, that's just about all that we know at this point: that cephalopods appear to have biphasic memories, meaning that the behavioral evidence of short-term memories can be dissociated from that of long-term memories.  This is hardly (by itself) a basis on which we can imply any sort of consciousness or advanced cognitive capacity, as animal-rights supporters who mention this fact seem to imply.

          In interpreting these results in the context of our knowledge of cephalopods as a whole, we should keep in mind what is meant by short- and long-term memory in humans.  Short-term memory is what happens when newly learned information is bouncing around the cortex somewhere, being continually processed but not permanently encoded somewhere.  These memories will disappear if they are not rehearsed (or otherwise actively retained).  Long-term memory has been (relatively permanently) encoded into neural circuits, so that it can be retrieved after periods when it has not been actively processed in short-term (or working) memory circuits.  These processes have been studied intensely in humans, and can be precisely because we have a complex cognitive system build around them (or on top of or parallel to them, depending on who you ask) that we can access.  As of yet, we don't have the experimental techniques to assess exactly how "human-like" or "vertebrate-like" cephalopod memory systems are, because we can't study them in nearly as much detail as language-based and other cognitive tasks allow us to in humans.  Thus, making any strong conclusions about the nature of cephalopod memory other than that it appears to be multiphasic (with no implied "and-so-cephalopods-are-smart-like-people") is untenable.

          Lastly, I find it frustrating that animal rights activists use our (very primative) knowledge of cephalopod memory systems to try to support their position that eating cephalopods is wrong.  Not only is it an inconclusive (what does memory have to do with suffering and morality?) and nonspecific argument (did anybody think that ungulates, swine and birds don't have complex memory systems?), but it misses some of the big points that the animal rights movement has taught us.  First of all, it implies that cephalopods are somehow special because they are intelligent and human-like.  However, having compassion for animals explicitly demands that we not judge their worth by analogy to our own abilities - this has proved to be an attitude that encourages cruelty to animals simply because we are ignorant of them and their behavioral and cognitive capacities.  If we didn't know about cephalopod memory systems, would they still be worth defending from fishing and consumption as food?  Hopefully, the answer is yes - so why try to use this (admittedly inadequate) argument now that we conveniently have information that appeals to one's emotional predispositions?  I find this to be irresponsible and counter-productive, as it diminshes the credibility of other, more valid arguments against the consumption of cephalopods (or any animal, for that matter) that animal rights activists might use.

          Sorry if this was a bit heavy on editorial material.  Being very concerned about animal welfare myself, I get annoyed when people make the cause look stupid by saying things that are ill-informed, ill-reasoned, or just plain wrong.  Although I wish that people would stop killing cephalopods for food, spinning information to try to get people to agree with a point is dishonest, and at best a very poor strategy for debate, as there's bound to be at least one attentive person on the other side who will point out that you're not being true to the facts - and nobody will listen to you after that.

Thanks for reading!
SHOMRAT, T., ZARRELLA, I., FIORITO, G., & HOCHNER, B. (2008). The Octopus Vertical Lobe Modulates Short-Term Learning Rate and Uses LTP to Acquire Long-Term Memory Current Biology, 18 (5), 337-342 DOI: 10.1016/j.cub.2008.01.056

J. Z. Young (1970). SHORT AND LONG MEMORIES IN OCTOPUS AND THE INFLUENCE OF THE VERTICAL LOBE SYSTEM Journal of Experimental Biology (52), 385-393

Crook, R., & Basil, J. (2008). A biphasic memory curve in the chambered nautilus, Nautilus pompilius L. (Cephalopoda: Nautiloidea) Journal of Experimental Biology, 211 (12), 1992-1998 DOI: 10.1242/jeb.018531

Saturday, July 10, 2010

Antarctic octopus venom

In my recent quest to find new, cutting-edge research on cephalopods, I've come across some neat stuff (check out this post on the perception of polarized light by cuttlefish - it's one of my favorite new cephalopod research topics!)  The study I'll review here is outside of my field of relative expertise, but it's so neat and so new that I couldn't resist writing about it.  It's good to step out of one's comfort zone every once in a while, right?

An international team of researchers hailing from Norway, Australia, and Germany has published a study on the venom of Antarctic octopods (more accurately, it is being published, though it hasn't hit the presses yet.)  The team investigated the biochemical properties of extracts from the salivary gland of four Antarctica octopus species and wrote up their results in Venom on ice: First insights into Antarctic octopus venoms (2010).

Here is their image of the posterior salivary glands of an octopus, from which the authors collected all of their specimens:

These glands produce a variety of compounds, notably venom and digestive enzymes.  The venom of temperate-water octopuses has been studied in the past.  Never before, however, has venom been studied in an octopus that lives in below-freezing temperatures, conditions under which the enzymes in most venoms work very poorly if at all.  To begin to understand the role of venoms in the lives of Antarctic octopuses, the team collected and tested venom from four octopus species collected off the Antarctic shore: Adelieledone polymorpha, Megaleledone setebos, Pareledone aequipapillae, and Pareledone turqueti.  Here are images of some of their specimens:

Cute, aren't they?  Octopods always are!  Anyways, back to the biochemical assays.

First, the authors tested the extracts for alkaline phosphatase (ALP) activity.  ALP is an enzyme that is in spider and snake venom that is thought to help immobilize prey items.  Second, they tested for Acetylcholinesterase (AChE) activity.  AChE breaks down acetylcholine, a neurotransmitter, potentially acting as a toxin by disrupting neuromuscular function.  Third, the extracts were tested for general proteolytic activity using casein.  Fourth, an assay for secreted phospholipase A2 (sPLA2) was performed.  sPLA2 is found in cone snail and snake venome, and contributes to the effects of venoms in a variety of ways.  Finally, the researches assessed whether the venoms showed haemolytic activity, which is a common marker of the general toxic activity of venoms.  Taken together, these results should begin to characterize the putative venom of each octopus species.  After all of this, the researchers reviewed what is known about the morphology of the mouthparts of the octopuses, as well as their feeding habits, and tried to relate these to their biochemical findings.


So, after all of that, what did they find?  Here are their results(takes another deep breath):

Venom from all of the species had some ALP activity.  Interestingly, however, when ALP activity was tested at 0 Celsius and at 37 Celsius, venom from 3 species of octopus (A. polymorpha, M. setebos, and P. turqueti) had higher ALP activity at the lower temperature!  This is a significant finding because it suggests some sort of modification of the proteins responsible for this activity to function optimally at a lower temperature.  This lends some weight to the theory that the use of venom has been important enough to the survival of Antarctic octopus species that they have evolved enzymes to work under conditions where most enzymatic toxins would not.  In the other tests, an essentially similar pattern of results were found, except for the AChA activity assay.  Little AChA activity was found in any of the species, although the results of the assay were poor enough (that is, inconsistent) that they were not included in the paper.  Interestingly enough, although all of the species had a few potentially functional toxins in their venom, most of them showed only weak haemolytic activity.  Only one extract (from P. turqueti) showed strong haemolytic activity.

The relation of venom activity to morphology and diet that the authors attempted to point out appears to be weak (or at least difficult to point out given their sample,) as it is mentioned that few clear venom-related adaptations in diet or anatomy were present in these octopus species.  A. polymorpha is noted to have a very large salival gland and a narrow beak, which the authors suggest might be an adaptation associated with the use of venom as a primary means of catching prey (as opposed to having powerful jaws to physically overpower the prey.)  This species feeds mostly on amphipods and polychaete worms, and so it's unclear why it would rely on venom to subdue such (relatively) easy going prey instead of retaining a more varied diet.  In any case, though, this is one of those papers that, being exploratory, raises many more questions than it answers - that's the kind I like!

What I find most interesting about this work is that it begs questions about the evolution of octopus venom.  How quickly could the octopus populations move into cold water?  Was this limited by the evolution of venom enzymes, or did that evolution occur after some quicker relocation of the species which left their warm-water-adapted enzymes useless?  Did A. polymorpha's ancestors have a specialized diet before they became Antarctic, or is that only a successful feeding strategy in the Antarctic environment?  The world may never know (although I hope we do, someday!)

Thanks for reading!
Undheim, E.A.B., et al. (2010). Venom on Ice: First insights into Antarctic octopus venoms Toxicon