Duck beaks, Umwelt and Kantian a prioris

by Matthew Cobb

This article from the scientific journal Cell Reports, by Eve Schneider and colleagues from Yale, popped into my inbox this evening. I could see that it was about ducks and evolution, so I thought it would interest Jerry. It turns out to be pretty fascinating, and it tells us something important about how the sensory worlds of different species are shaped by evolution, as I’ll explain below. It’s open access, so anyone can read it. Click on the image below if you want to read the PDF.

One of the nice features about this article is that it has a “graphical abstract”. Several of the journals from the Cell stable use these abstracts, and I must admit this is the first one I have actually found useful. You can see why: it RHYMES:The study looked at seven different species of duck (including the mallard) which have different food preferences – some of them dive, some dabble (Pekin ducks [domesticated mallards], it appears, forage solely in darkness). Here they are, in a figure from the paper:

The hypothesis was that all these species, which rely particularly on the sense of touch, would have more cells capable of detecting touch (“mechanoreceptors”, in the jargon) in the trigeminal nerve that innervates the beak. Touch works through a particular gene called Piezo2, which codes for what is called an ion channel—these are the tiny pores in nerve cells that enable them to work.

They found that all these species have more of the Piezo2 neurons than do chickens, which do not seem to rely so much on tactile stimulation. There were also differences between the ducks: the Pekin duck, which forages solely in darkness, had the highest proportion of these neurons, while the wood duck, with its narrow bill, had the smallest number.

This expansion of touch neurons in ducks has not come free of charge, however: the ducks seem to have lost corresponding numbers of neurons that, in chickens, detect pain and temperature. In other words, there is an evolutionary trade-off. You don’t seem to be able to have lots of every kind of receptor. What the downsides are of not being able to feel pain or temperature so intensely if you are a duck is not clear. Whatever they are, they are presumably less significant than the advantage of being able to sense your prey more accurately as you dabble or dive.

This is not only a nice bit of evolutionary biology (and a cute graphical abstract), it is also a great example of how the sensory worlds of different animals provide completely different insights into the world. In the 1920s, the Estonian biologist Jakob von Uexküll described what in German was called the Umwelt or inner sensory world of each species, which was rooted in its ecology. This concept is now a fundamental starting point of modern sensory ecology and helps us understand how natural selection has shaped brains and nervous systems, and, when it comes to other animals, how we think of what it is like to be, say, a duck.

The significance of the idea goes far deeper, as Uexküll acknowledged. He saw a link with an idea developed by the German philosopher Immanuel Kant. In his Critique of Pure Reason, published in 1787, Kant argued that some features of how we perceive are given a priori, that is, without experience.

Although Kant was primarily interested in things such as space, time and moral judgements, and ended up placing a profound divide between perception and the material world, he put his finger on a key feature of what is happening when we —or ducks—interact with the world. Our senses are not open valves that simply allow all stimuli into our brain; instead we perceive only certain parts of our environment.

Many scientists have subsequently referred to what are called in the jargon ‘the Kantian synthetic a prioris’: nervous systems involve an innate cognitive and neurobiological framework that filters and processes raw sensory stimuli to turn them into a picture of the world. And that picture differs from species to species.

I’m not sure Kant would have been impressed that his idea had been validated in ducks, but that is what Eve Schneider and her colleagues have done.

__________

Schneider, E. R. et al. 2019. A Cross-Species Analysis Reveals a General Role for Piezo2 in Mechanosensory Specialization of Trigeminal Ganglia from Tactile Specialist Birds. Cell Reports Volume 26: 1979-1987.,

34 Comments

  1. Posted February 20, 2019 at 8:34 am | Permalink

    What a lovely piece. I’m incorporating that into my first year ecology lectures, if you dont mind!

  2. Dominic
    Posted February 20, 2019 at 9:21 am | Permalink

    Very interesting!

    There is a nice drawing of a duck from Orkney here on Twitter today…

  3. Michael Fisher
    Posted February 20, 2019 at 9:30 am | Permalink

    Thank you Matthew.

    I had no idea until today that [some parts of?] the outer surface of the duck bill [or is it all birds?, many birds?] is covered in smooth, hairless, rubbery skin with various receptors dotted about. Akin to the pads on human fingertips I suppose.

    Something interesting from 2014 HERE :-

    …In most birds and mammals, the majority of trigeminal neurons are devoted to temperature and pain perception. On the other hand, an overwhelming proportion of trigeminal neurons in ducks are specialized for light touch sensation. The unusual pattern observed in the ducks matches that found in star-nosed moles […] But ducks didn’t just have more neurons devoted to detecting physical force in their bills. The neurons they had actually functioned more efficiently, displaying a much stronger response to a light touch than the corresponding neurons in most other birds and mammals would. “In the absence of all other components of the skin, the [duck bill] neurons alone are capable of converting force into excitation much more efficiently than in a mouse” […] which particular proteins might be involved in mediating the duck’s extremely strong sense of touch.

    One promising candidate is an ion channel called Piezo2, which has also been shown to influence mechanosensation in mice. It’s present at low levels in visual food-foragers like chickens, as well as in duck neurons not connected to the beak’s sensory system. But the vast majority of duck trigeminal ganglion neurons express the channel, suggesting that it may contribute to specialized touch sensation.

    However, Bagriantsev emphasized that Piezo2 is likely not the full story. “Piezo2 in mice generates fast-decaying currents — the channel opens, then closes quickly. But what we see in this duck is that the current persists and the channels stay open,” he explained. “That means either that duck Piezo2 is significantly different from mouse, or that duck neurons have other mechanosensitive ion channels”

  4. BJ
    Posted February 20, 2019 at 9:31 am | Permalink

    Huh. I read that title as Duck beaks, Umwelt and a Kantian penis, and thought to myself, “this is going to be a very interesting article.” It was still interesting, but I’d love a postmodern paper on how the Kantian Penis shapes our inner sensory experience, and in turn intersects with ducks, white supremacy, and patriarchal heteronormativity.

  5. Posted February 20, 2019 at 9:34 am | Permalink

    [note: i am not challenging the finding of this science. I am challenging that it “validates” Kant.]

    Validation of Kant on synthetic a prioris requires a different process than observing ducks.

    It requires faith. Kant’s neo-Platonic beliefs stipulate knowledge prior to “anything,” which means you are born with information, which means a supernatural realm.

    Meanwhile, ‘ducks’ exist in reality.

    • Posted February 22, 2019 at 11:59 am | Permalink

      Innate ideas do not require supernaturalism; however, Kant’s version does (because the whole thing does).

      • Posted February 22, 2019 at 12:16 pm | Permalink

        Okay, let me change my formulation:

        A claim for synthetic a prior knowledge requires dualism.

        I probably should have said “dualism” in the first place, but dualism is subsumed under the wider term “supernatural.”

        The only view from which “innate ideas do not require supernaturalism” is a buy-in. Kant goes to some length [/s] to construct the appearance of objectivity for his a priori (innate) content. However, he was religious, dualistic, and Platonic, so …. no.

  6. Posted February 20, 2019 at 9:41 am | Permalink

    This is interesting. I wonder now if ducks are also able to detect the minute electrical fields around aquatic insects and crustaceans. Like the duck-billed platypus and other animals that forage for invertebrates in this fashion.

    • Posted February 23, 2019 at 8:32 am | Permalink

      Hi Mark,

      I’ve been seriously wondering about this myself…. If any students in your program might be interested in working on this for a PhD, or other aspects of sensory biology in birds please consider sending them my way!

      https://bio.as.uky.edu/users/esc258

      Best wishes,
      Eve

  7. Christopher
    Posted February 20, 2019 at 9:42 am | Permalink

    So could we expect to find (or have already found) similar analogous adaptations of nerve cells in other animals that use similar tactile foraging techniques, like the star-nosed mole, platypus, or maybe the walrus?

    And as for the reduced pain and temperature sensation, I’m just speculating, but do all these species experience cold winter weather when reduced sensations could be beneficial or at the very least not detrimental?

    • darrelle
      Posted February 20, 2019 at 10:03 am | Permalink

      See Michael Fisher’s comment above, number 3.

      He references an article that says, among other interesting things, that ducks and star-nosed moles do in fact share this unusual tactile specialized trigeminal neuron feature.

      • Christmas
        Posted February 20, 2019 at 12:28 pm | Permalink

        Yeah, I saw that. He must have posted while I was still typing. I tried reading a bit of the paper but it’s waaay over my head.

      • Christopher
        Posted February 20, 2019 at 12:29 pm | Permalink

        Yeah, I saw that. He must have posted while I was still typing. I tried reading a bit of the paper but it’s waaay over my head.

    • Michael Fisher
      Posted February 20, 2019 at 11:43 am | Permalink

      “And as for the reduced pain and temperature sensation, I’m just speculating, but do all these species experience cold winter weather when reduced sensations could be beneficial or at the very least not detrimental?”

      Fewer pain & temp receptors doesn’t necessarily equate to a lessened sensation from the POV of a duck’s internal perception [its mind].

      Similarly [but not the same] I would suppose [I don’t know] that the ‘gain signal’ of a receptor can vary across species, maybe to reflect the importance of the signal to the creature. So from my comment #3 I quoted this from the link I provided:

      “In the absence of all other components of the skin, the [duck bill] neurons alone are capable of converting force into excitation much more efficiently than in a mouse”

      • Christopher
        Posted February 20, 2019 at 12:32 pm | Permalink

        Thanks for explaining that. I wish I could finish my biology degree, maybe need less help in understanding some of the papers shared here but until then I’ll just have to suffer from science envy.

  8. Posted February 20, 2019 at 9:44 am | Permalink

    Great stuff, and explication. And, there’s a merganser!

  9. John S
    Posted February 20, 2019 at 10:40 am | Permalink

    So it seems (overstating things a bit, perhaps) that Philosophy (Kant) first came up with a scientific inference that was testable, and true.

    Maybe the Templeton boys will be the next producers of valid science inferences?

    Or maybe not. (I don’t think I’ll bother to apply for a grant.)

    • Posted February 22, 2019 at 12:00 pm | Permalink

      The article oversimplifies Kant, whose philosophy is really not very science friendly at all. However, the notion of innate ideas can be found in Plato and Descartes (etc.) as well. Chomsky explicitly makes use of this legacy in his discussion of language acquisition.

  10. Posted February 20, 2019 at 11:44 am | Permalink

    “This expansion of touch neurons in ducks has not come free of charge, however: the ducks seem to have lost corresponding numbers of neurons that, in chickens, detect pain and temperature. In other words, there is an evolutionary trade-off.”

    Rather than a trade-off, it seems likely that the two come together naturally. It would not be advantageous for the duck to feel pain every time it jammed its bill into the river bottom. Such a duck might choose not to forage in order to avoid pain.

    I have noticed something similar in cats’ noses. Our noses are very sensitive and we don’t like to get hit there even gently. Cats, on the other hand, bump their noses into things all the time and don’t seem particularly bothered by the experience. My guess is that their noses, like duck bills, are evolved for touch and pain is not felt as strongly as it is in humans.

  11. Steve Gerrard
    Posted February 20, 2019 at 12:05 pm | Permalink

    Trigeminal neuralgia in humans is certainly a miserable condition, often described as having your face on fire – or half of it, as it usually affects one side. It can be triggered by a small, otherwise benign growth that bumps into the nerve, which has branches all over the face. I’m not sure I see the benefit of having such a sensitive nerve in the face. If ducks don’t need it, why do we?

    • Posted February 20, 2019 at 12:12 pm | Permalink

      Humans have evolved to make faces, and recognition of others’ faces, of huge social and survival importance. This resulted in a need to protect our faces. Their sensitivity reflects that priority. In short, “Hit me anywhere but not in the face!”

    • Michael Fisher
      Posted February 20, 2019 at 12:59 pm | Permalink

      The below two-point discrimination diagram for humans Steve. If two compass needles are pressed to the skin we can discriminate them as two points if the needle gap is sufficient & nerve density is great enough. The numbers up the left side is the needle gap.

      Red bar: Pain
      Blue bar: Touch

      You can see that the smallest gap [biggest sensitivity] is fingertips, then hands [palms] & then forehead, shoulders & soles of feet. Note that the back of the hands & the forearms are fairly insensitive.

      The source for the diagram says the parts of the body used most to explore surroundings are the most sensitive. Going through undergrowth at dusk one would put up the forearms & back of the hands to protect the head where most of are critical faculties & senses are located.

      • Michael Fisher
        Posted February 20, 2019 at 1:02 pm | Permalink

        are our

        • Mark R.
          Posted February 20, 2019 at 5:16 pm | Permalink

          It seems counter intuitive to me that the calf would have the highest pain/touch threshold. Why would that be? I understand the forearm regarding walking trough undergrowth and such, but no one walks backwards. You’d think the thigh threshold would be higher or at least as high as the calf. Hmmmm.

          • Michael Fisher
            Posted February 21, 2019 at 3:30 am | Permalink

            You didn’t read my notes above the pic 🙂

            …two-point discrimination […] two compass needles are pressed to the skin we can discriminate them as two points if the needle gap is sufficient & nerve density is great enough. The numbers up the left side is the needle gap.

            Red bar: Pain
            Blue bar: Touch

            You can see that the smallest gap [biggest sensitivity] is fingertips…

            Thus least pain sensitivity [red bar] is the bridge [dorsum] of the foot & the least touch sensitivity [blue bar] is the calf.

            • Mark R.
              Posted February 21, 2019 at 3:19 pm | Permalink

              Oh…thanks for the clarification.

          • Michael Fisher
            Posted February 21, 2019 at 3:34 am | Permalink

            I would say the back of the foot & the calf are analogous to the back of the hand & the forearm. Perhaps we’re most insensitive as a semi-all fours creature still?

    • Michael Fisher
      Posted February 20, 2019 at 1:07 pm | Permalink

      Incidentally, I have nerve damage to the left side of my face since 1977. When I shave that area I get the nauseas sensation that one normally gets by sticking a finger to the back of the throat. Shaving that cheek also gives me a salty metallic taste on the tongue. The back of the throat, the back of the tongue & parts of the cheek share the same ‘trunking’ across the face/skull.

      • infiniteimprobabilit
        Posted February 21, 2019 at 2:24 am | Permalink

        Does that mean you’re getting ‘crossed wires’ – adjacent nerves shorting out?

        cr

        • Michael Fisher
          Posted February 21, 2019 at 3:21 am | Permalink

          I have no idea about the mechanics of it. The wiring goes from C5 & higher under the collarbone and into the armpit. From there, they branch out into individual nerves that control the muscles in the shoulder, elbow, wrist and hand. But some taste & touch wires seem to service the cheek & back of the tongue – I assume they branch off & head north before the collarbone. The damage is near the spine itself & the brain hasn’t a clue what to make of the signal – perhaps it’s the brain’s fault.

  12. CAS
    Posted February 20, 2019 at 4:58 pm | Permalink

    Nice paper!

  13. Mark R.
    Posted February 20, 2019 at 5:24 pm | Permalink

    That was and interesting read.

    I also noticed umwelt on one of Jerry’s captions of a cat fight on Hili’s dialogue. I declare it the word of the day.

  14. Posted February 21, 2019 at 2:33 pm | Permalink

    Interesting! We show our students slides with the modified skin at the base of duck bill rich at mechanoreceptors (Herbst and Grandry corpuscles).


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