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Apr 15 2013

Mary’s Monday Metazoan: Ol’ Three-Eyes

It’s a frog tadpole with an eye surgically grafted to its trunk!

ol3eyes

Wait, this is an old story — similar experiments were done at least 20 years ago. You can transplant developing eyes to the tadpole, but the cool thing is that the donor optic nerves will grow into the sensory tracts of the dorsal spinal cord and grow anteriorly to the optic tectum, where they will make functional connections. Not, as I recall, adequate for image formation, but at least good enough that the tadpole will startle if a light is flashed at the eye in its tail.

I did kind of go “ugh” at the spin the story put on it, though: that it could lead to a medical breakthrough that would allow blind people to see! Nope. Frogs already readily accept eye grafts and regrow the connections; there are lots of experiments where, for instance, you cut out the adult frog eye, severing the optic nerve, and reinsert it upside down, and the nerves grow back and build new, functional connections. That’s the hard part, getting operational regrowth. Planting ectopic eyes is trivial.

23 comments

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  1. 1
    chigau (違う)

    Ivory tower.
    Vivisection.

  2. 2
    lemian

    ‘Planting ectopic eyes is trivial.’

    Of course. everybody knows the problem is getting them to bloom.

    I had no idea this was possible (I’m a bio-noob), so hats of to tadpoles.

  3. 3
    Andy Groves

    Plantig ectopic eyes is indeed trivial.

    This, on the other hand, is very cool.

    http://www.ted.com/talks/sheila_nirenberg_a_prosthetic_eye_to_treat_blindness.html

  4. 4
    DLC

    “tadpole 2.0.now with rear vision for reversing! “

  5. 5
    Dave White

    Another non-biology noob here, but this does sound cool. Is there a way to gauge the functionality of these eyes? If so, how would it relate to the cochlear implants available for the deaf?

  6. 6
    Artor

    I’m curious as to what happens to the eye when the tadpole metamorphoses and no longer has that tail. Does the eye get reabsorbed, or does it move to the frog’s butt? Does it ever develop eyelids & motor muscles?

  7. 7
    txpiper

    “I’m curious as to what happens to the eye when the tadpole metamorphoses and no longer has that tail. Does the eye get reabsorbed, or does it move to the frog’s butt?”
    .

    This is perhaps the most intriguing inquiry I’ve ever personally seen on Pharyngula. I’ve often wondered if genuine interest and curiosity can overcome canned answers, especially in regards to the plausibility of random DNA replication errors resulting in such things as “the nerves grow back and build new, functional connections”.

  8. 8
    chigau (違う)

    txpiper

    …overcome canned answers…

    bwahahaha

  9. 9
    txpiper

    No, really chigau. The method should be very conservative and demanding. I’ll show you; look at this:

    ”But if you want to know what caused the Cambrian explosion, I can give you the short answer…..What it was was environmental changes, in particular the bioturbation revolution caused by the evolution of worms that released buried nutrients, and the steadily increasing oxygen content of the atmosphere that allowed those nutrients to fuel growth; ecological competition, or a kind of arms race, that gave a distinct selective advantage to novelties that allowed species to occupy new niches; and the evolution of developmental mechanisms that enabled multicellular organisms to generate new morphotypes readily.”

    Announcents don’t cut it, and when you get them, you should respond with the icy demands proposed in one of PZ’s earlier posts:

    “Share your procedure so I can assess and replicate it, which is what scientists are supposed to do.”.

    You should be in line to inquire about the replicatable evidence, which you will never see. But more importantly, you should be curious about the not-so-subtle inference that a changing environment influences the character of random mutations, which of course, it cannot. In other words, you don’t get what you need because a niche is available. Random, however irritating it might be, means random. Things don’t just evolve. If you think otherwise, stick to the stricture and respond to proclamations with “Share your procedure so I can assess and replicate it, which is what scientists are supposed to do.”.

    You should also be curious about what supposedly happened in the ‘Cambrian’. This was not just rapid speciation. This is supposed to be a phenomenal radiation of Phyla, one click below Kingdom, but above Class, Genus, Order, Family and Species. And these Phyla occur with no evidence in the way of antecedents. Isn’t that right? Where did all the new genes and gene families come from, and what was the mechanism that produced them? Gene duplication? GD only expects more impossibly happy mutations to render a copied gene into something wonderful, right?

    I have to wonder chigau, whether you’ve ever actually had original thought, or asked a legitimate question.

  10. 10
    Monsanto

    I read the Nat Geo article, and we’re in for an exciting future. Soon we’ll be able to make a Tri-Klops and finally defeat He-man.

  11. 11
    PZ Myers

    If eyes are transplanted to tails, they’re lost at metamorphosis. I’ve seen studies where ectopic eyes are transplanted to tadpole crania, though, and those persist through metamorphosis, and you can do electrophysiological recordings of activity from the weird eye in the tectum.

    txpiper is an idiot. There is evidence of antecedents; the molecular data, and as well, the fossil record shows a gradual emergence of new forms over tens of millions of years in the Cambrian. The book by Valentine, On the Origin of Phyla, gets right into his fallacy — the division into species, genus,…phyla is in some ways highly arbitrary, and the position in the hierarchy is largely dependent on the magnitude of the temporal distance. 600 million years ago, the first vertebrate and first arthropods would have been seen as sibling species, and a pre-Cambrian taxonomist wouldn’t have put them into separate phyla at all.

  12. 12
    ChasCPeterson

    600 million years ago, the first vertebrate and first arthropods would have been seen as sibling species,

    To clarify: the first vertebrate and the first arthropod were never sibling species.
    I guess you mean the urprotostome and the urdeuterostome. Neither of which looked anything at all like a vertebrate or srthropod. As you know.

  13. 13
    David Marjanović

    especially in regards to the plausibility of random DNA replication errors resulting in such things as “the nerves grow back and build new, functional connections”.

    Nerves grow in certain directions as some substances from the outside trigger growth toward them. Random mutations make nerves grow in different directions (in response to different substances). Those optic nerves that grow toward those parts of the brain that can do something with their information allow the animal to see, and seeing animals have – in most environments – a clear reproductive advantage over blind ones.

    Any more questions?

    Really?

    look at this:

    Where is it from?

    Announcents don’t cut it

    These “announc[em]ents” weren’t generated by rectal extraction. They’re based on lots of evidence that you need to read up on. Google is your friend.

    But more importantly, you should be curious about the not-so-subtle inference that a changing environment influences the character of random mutations, which of course, it cannot.

    How many more dozens of times do we need to repeat it till you finally listen?!?!? The environment does not influence which mutations happen, we’ve never claimed so, and the theory of evolution does not need such an impossible thing to happen at all!!!

    I repeat: For the theory of evolution to work, it is not necessary that mutations ever, under any circumstances, be anything but random. Mutations are random, they follow Murphy’s Law. Mutation generates diversity, and selection restricts this diversity – in different ways in different environments.

    Things don’t just evolve.

    PZ, who do I need to kill to get Comic Sans?

    txpiper, this is such a stupid thing to say. Things that reproduce and inherit do indeed just evolve. They can’t fucking help it! I’ve seen it happen with my own eyes, as I’ve really explained often enough.

    This was not just rapid speciation. This is supposed to be a phenomenal radiation of Phyla, one click below Kingdom, but above Class, Genus, Order, Family and Species.

    This, too, is a deeply stupid thing to say – however, you’re in great company: Stephen Jay Gould made the same mistake once, “pointing out” the “fact” that no new “phyla” had evolved since the Cambrian.

    Richard Dawkins pointed out what a stupid thing that was to say: he compared it to looking at an old oak and saying it hadn’t grown really thick limbs in a hundred years, only puny branches and tiny twigs.

    Kingdoms, phyla, classes, orders, families and genera don’t exist in nature. They only exist inside some people’s skulls. They do not have definitions, they are only mnemonic devices – and misleading ones at that. Once a taxonomist feels a group is diverse enough, they declare it a phylum or whatever, and their colleagues can agree with this or not, it’s just personal preference. Obviously, the older a group is, the more diverse it can be, because evolution accumulates change. In other words, roughly speaking, groups are called “phyla” because they’re of Cambrian age. Trying to explain why so many “phyla” originated in the Cambrian would be bass-ackwards.

    Even species are a mess. The higher ranks don’t have definitions – but the word “species” has about 150 different definitions, and depending on which definition you use, there are from 101 to 249 endemic bird species in Mexico.

    And these Phyla occur with no evidence in the way of antecedents. Isn’t that right?

    No.

    As usual, your sources are outdated. Here’s Kimberella, a mollusk fifteen million years older than the Cambrian. Mollusca is traditionally classified as a phylum.

    Another traditional phylum is Arthropoda. In the early-middle Cambrian, you find animals that are closely related to Arthropoda, but not members of it if you don’t want to stretch the term a lot. You even find animals that are closely related to the three traditional phyla Arthropoda, Tardigrada and Onychophora, but members of neither. I’m talking about the anomalocaridids, the “armored lobopods”, Opabinia, Aysheaia, and the palaeoscolecids. We’re looking at a tree, and Arthropoda, Tardigrada and Onychophora are just the three twigs that are still alive.

    Which brings me back to my favorite point, a point I’ve made to you plenty of times and which you’ve never commented on:

    The similarities between organisms are arranged in a tree shape. Why a tree? Why not a line, a tape, a circle, a cross, a star, a net? Why a tree, the one and only shape predicted by the theory of evolution?

    Where did all the new genes and gene families come from, and what was the mechanism that produced them?

    Mutation, including gene duplication and genome duplication. As usual. Let me add that you seem to drastically overestimate how many new genes were required.

    Gene duplication? GD only expects more impossibly happy mutations to render a copied gene into something wonderful, right?

    You still have no idea how common mutations are. It’s enough if a small fraction of them are “happy”.

    You still have no idea, even though we keep pointing out to you that you have from 100 to 200 mutations that both of your parents lack.

    I have to wonder chigau, whether you’ve ever actually had original thought, or asked a legitimate question.

    I have to wonder, txpiper, whether you’ve ever tried to sit down and read anything for comprehension. I have to wonder if you’ve ever sought out new information (as opposed to sentence fragments that you could claim supported your positions). I have to wonder if you’re afraid of something.

  14. 14
    David Marjanović

    you mean the urprotostome and the urdeuterostome. Neither of which looked anything at all like a vertebrate or srthropod.

    Even today, flatworms and Xenoturbella look very similar.

  15. 15
    Markita Lynda—threadrupt

    Shorter: What a lot of rot txpiper does talk!

    Also remember Wiwaxia, which by its rasping tongue I suspect to be on the ancestral branch of snails.

    font=”Comic Sans MS” with appropriate wrappers might work.

    I suspect that another cause of the Cambrian explosion, if you can call something an explosion that probably took ten million years and had deep roots in previous evolutionary history, was the development of hard parts, e.g. exoskeletons, that gave anchorage for muscles, allowed elaborate structures, produced biting or pinching surfaces, and enabled the growth of armor, spikes, and other counter-predator structures.

  16. 16
    David Marjanović

    The rasping tongue (radula) is common to all molluscs (except where secondarily lost); Kimberella appears to have it, and radula scratch traces are known from the same time and the same places.

    But it’s great that you bring up Wiwaxia, because it and other weird animals with fringed scale thingies have been suggested to lie around the ancestry of the traditional phyla Brachiopoda, Annelida and Mollusca.

  17. 17
    Owlmirror

    You should also be curious about what supposedly happened in the ‘Cambrian’.

    In scare quotes, yet.

    Still a radiometric dating denialist, eh?

  18. 18
    Nerd of Redhead, Dances OM Trolls

    I have to wonder chigau, whether you’ve ever actually had original thought, or asked a legitimate question.

    I have to wonder chigau, whether you’ve ever actually had original thought, or asked a legitimate question.This from the unscientific presuppositional godbotting creobot txpiper? Bwahaahahahahzaha.

    What a comic you are. You haven’t had an original thought in your life. Your intellect is nothing but pretense. Your deity doesn’t exist, and you can’t prove it does. All you have is your falacious beliefs and mindless slogans. Pitiful….

  19. 19
    anteprepro

    I have to wonder chigau, whether you’ve ever actually had original thought, or asked a legitimate question.

    txpiper’s doubled down on their lack of self-awareness, I see. Hilarious!

  20. 20
    ChasCPeterson

    flatworms and Xenoturbella look very similar.

    A couple of recent studies have put some or all of the acoels together with X. as basal deuterostomes.

  21. 21
    ChasCPeterson

    (of course, it’s long-branch city, but still)

  22. 22
    PZ Myers

    Yep. They would have been a pair of worms, subtly different from one another, but each founding a phylum.

  23. 23
    Ing

    @davewhite

    Taking a guess that you could expose it to stimuli and see if the tadpole reacts?

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