How do you make a cephalopod drool?

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We’re all familiar with Pavlov’s conditioning experiments with dogs. Dogs were treated to an unconditioned stimulus — something to which they would normally respond with a specific behavior, in this case, meat juice which would cause them to drool. Then they were simultaneously exposed to the unconditioned stimulus and a new stimulus, the conditioned stimulus, that they would learn to associate with the tasty, drool-worthy stimulus — a bell. Afterwards, ringing a bell alone would cause the dogs to make the drooling response. The ability to make such an association is a measure of the learning ability of the animal.

Now…how do we carry out such an experiment on a cephalopod? And can it be done on a cephalopod with a reputation (perhaps undeserved, as we shall see) as a more primitive, less intelligent member of the clade?

The nautilus, Nautilus pompilius despite being a beautiful animal in its own right, is generally regarded as the simplest of the cephalopods, with a small brain lacking the more specialized areas associated with learning and memory. It’s a relatively slow moving beast, drifting up and down through the water column to forage for food. It has primitive eyes, which to visual animals like ourselves seems to be a mark of less sophisticated sensory processing, but it has an elaborate array of tentacles and rhinophores which it uses to probe for food by touch and smell/taste. Compared to big-eyed, swift squid, a nautilus just seems a little sluggish and slow.

So let’s look and see how good a nautilus’s memory might be. First, we need a response to stimuli that we can recognize and measure, equivalent to the drooling of Pavlov’s dogs. While they don’t measurably salivate, the nautilus does have a reaction to the hint of something tasty in the water — it will extend its tentacles and rhinophores, as seen below, in a quantifiable metric called the tentacle extension response, or TER.

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The scoring system for tentacle extension response (TER) in chambered nautilus. TER was graded every 5 s from a minimum score of 0 to a
maximum score of 3. Each level corresponds to a range of percentage extension relative to the length of the animalʼs hood. Zero is recorded when all
tentacles are retracted into their sheaths. A score of 1 corresponds to an extension of <33% of the hood length. A score of 2 corresponds to extension
between 34% and 66%, and 3 is given when tentacles are extended beyond 67% of hood length.

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Frontiers in cell biology

Alex Palazzo is talking about open questions in cell biology — in this case, control of organelle shape. Any of us who have poked around in cells know that it is not an amorphous blob of goo, but has characteristic, recognizable elements that we can see from cell to cell. What confers these stereotypic intracellular morphologies on organelles, and what are the functional consequences, if any?

(There are no jebons in there, so you don’t get to use those in your answer.)

Materpiscis attenboroughi

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It’s not often that something as delicate as details of the reproductive tract get preserved, but here’s a phenomenal fossil of a Devonian placoderm containing the fragile bones of an embryo inside, along with the tracery of an umbilical cord and yolk sac.

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(Click for larger image)

This is cool: it says that true viviparity, something more than just retention of an egg internally, but also the formation of specialized maternal/embryonic structures, is at least 380 million years old. Hooray for motherhood!

Here’s a reconstruction of what the animal would have looked like in life, as it is giving birth to its young.

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a, Diagram showing position of embryo and yolk sac within the mother. b, Artist’s reconstruction of Materpiscis gen. nov. giving birth.

Long JA, Trinajstic K, Young GC, Senden T (2008) Live birth in the Devonian period. Nature 453:650-652.

IEDG2008: Model systems are dead, long live model systems

I’ve discovered a couple of important things at this meeting.

One, late night sessions at west coast meetings are deadly for any of us coming from more eastern time zones. At least the morning sessions are low stress.

Two, I haven’t heard one Drosophila talk yet, and the message is clear: we’re now in the stage of evo-devo in which everyone is diversifying and chasing down a wide array of species. There was a bit of model-system bashing, but at the same time, everyone is acknowledging the crucial role of those traditional, but weird and derived, lab critters in providing a point of comparison and being the source of many of the tools being used to explore phylogeny now. I thought, though, that the smartest comment of the evening was that now everything is a model system.

I’ve got some dense piles of notes on the evening session, but I’m going to give you the short version of everything, with an emphasis on the novel twists.

Michael Akam talked about segmentation genes, which every developmental zoologist now knows inside and out — trust me, this is a familiar topic with over 25 years of detailed research … in Drosophila. Akam made the point that now it’s looking clear that three of the major segmented phyla, the arthropods, annelids, and chordates, may be using related genes to accomplish segmentation, but they seem to be using different mechanisms — so he considers the question of whether segmentation in these three is homologous is still an open question. He also discussed recent work on the centipede Strigamia (definitely not a lab animal: they can’t breed them in the lab yet, so all the work is done by collecting embryos in the field, in Scotland). They have a dynamic pattern of segment addition that is very different from what you find in flies, and more similar in some ways to chodate segmentation.

Chelsea Specht talked about floral evolution in the Zingiberales. I’m an animal guy, so even the most basic stuff in this talk was entirely new to me. I know the general rules of the spatial development of in the fruit fly of the plant world, Arabidopsis, and she gave us a bit of context there, reminding us of the concentric development of sepals, petals, stamens, and carpels. The Zingiberales are a large and diverse group of plants that includes bananas and ginger, and one characteristic is an extravagant modification of the canonical pattern, with extra stamens, a loss of select stamens, and a fusion of stamens to form a novel structure, the labellum, which in these plants functionally replaces the petals. So of course they’re looking into the genes involved in the patterns, which turn out to be the familiar Arabidopsis genes redeployed in new patterns.

Paul Sereno had a talk that took a very different tack, and was unfortunately giving it at the equivalent of 11:00pm Minnesota time, so I’m sorry to say I didn’t follow it carefully. He was discussing the analysis of morphology, and was advocating the development of tools and techniques to compare data sets in addition to the usual output, phylogenetic trees. He was making the case that a lot of morphological studies are actually very poor (a creationist in the audience would have loved it, largely because he wouldn’t have understood the context) because the input data sets of different studies are not comparable.

And now I have to get back to work and listen to the next set of talks.

Gerobatrachus hottoni

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It’s another transitional form, this time an amphibian from the Permian that shares characteristics of both frogs and salamanders — in life, it would have looked like a short-tailed, wide-headed salamander with frog-like ears, which is why it’s being called a “frogamander”.

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Complete specimen in ventral view, photograph (left) and interpretive outline drawing (right). Abbreviations: bc, basale commune; cl, cleithrum; cv, clavicle; dm, digital elements of the manus; dt3, distal tarsal 3; fe, femur; h, humerus; ic, intercentrum; il, ilium; is, ischium; op, olecranon process of ulna; pc, pleurocentrum; r, radius; sr, sacral rib.

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