Memorial day amphibian: the axolotl

May 30, 2011 • 12:40 pm

This beast is appropriate for Memorial Day because it’s on the verge of extinction, at least in the wild.  It’s the axolotl (Ambystoma mexicanum), now native to only a single lake near Mexico City. (It used to be in another lake as well, but that one was drained.)  Although it’s endangered in the wild, it’s bred profusely in captivity for both hobbyists and scientific research.

And it’s extremely cute.  This is a small one, and is probably a color mutant (several mutations are known in the species):

A lot of facts about the axolotl:

  • The salamanders are neotenic: that is, they become reproductive adults while retaining juvenile characteristics, notably the gills (see above) and a fin on the tail.  The axolotl is thus permanently aquatic, unlike most other salamanders, which metamorphose from gilled juveniles into a terrestrial adults.  I’ve often wondered how much genetic change was involved in the evolution of neoteny here.  Was it just one or two genes that kept the juvenile morphology but enabled reproductive maturity?  We know that you can induce axolotls to metamorphose by injecting them with thyroxine, a growth hormone, and it’s possible that the neotenic condition was produced simply by one or two evolutionary changes that inhibited production of this hormone.

Here’s a photo of a metamorphosed axolotl:

  • Axolotls are much beloved by developmental biologists for three reasons: they are easy to maintain and breed in captivity, they have large embryos that facilitate studying or teaching about development, and they have the remarkable property of being able to regenerate important body structures, including entire limbs. (Will this allow scientists, unlike God, to heal amputees?)  Click here to see a time-lapse movie of a limb regenerating, and go here to read more and see a movie about how the limbs regrow.  They also have the ability to heal wounds remarkably rapidly—sometimes within hours.  And they can regenerate large portions of the heart.  The implications for human health are profound but so far, I think, haven’t borne fruit.
  • The axolotl is the only species I know of whose common scientific name (at least in Western parlance) comes from the Aztec. (I’m sure there are others; I just don’t know of them.) One website says this:

“The name “Axolotl” comes from the Aztec language, “Nahuatl”. One of the most popular translations of the name connects the Axolotl to the god of deformations and death, Xolotl, while the most commonly accepted translation is “water-dog” (from “atl” for water, and “xolotl”, which can also mean dog).”

  • Axolotls are carnivores, can grow up to a foot long in the wild, and can live up to 15 years.

Here’s a video of scientists studying their regenerative abilities (note: there’s a small bit where the tail tip is amputated.  Note also how the researcher justify this mutilation):

The name of this animal always conjures up one of my favorite bits of doggerel, memorializing in words an experience we’ve all had. It’s by Richard Armour:

Shake and shake

The catsup bottle

First none’ll come

And then a lot’ll

48 thoughts on “Memorial day amphibian: the axolotl

    1. LOL again! Anyone who can come up with “kisses caudal” is my kinda poet. This thread is fast becoming a classic.

  1. The first axolotl is positively adorable! The bottom one looks very malicious and made me choke on my tea in fright.

    What does a metamorphosed axolotl look like?

    1. I posted one above; it looks pretty much like a neotenic one but without the gills.

      1. Mudpuppies, Nectorus sps., are significantly different from axolotls and are much more closely related to the neotenic tiger salamanders (both of them being Ambystoma, or mole salamanders)

          1. Yes! Thank you! Doc Storm’d kill me if he were still with us.

            And the one I remember best was in a habitat very much like the one in that lovely vid–thanks for that as well.

            I believe it was D. tenebrosus.

  2. They’re both cute, even the great bid adult version.

    I first learned about the axolotl from a silly little nursery rhyme. It was only when I got older that I realised that the song wasn’t entirely nonsense, but referred to a real critter and, rather more obliquely, to the thyroxine experiment.

    You never should attempt to put
    A quart size axolotl,
    Into an empty plastic bag
    Or in a pint size botl.

    It’s sure to kick up quite a fuss
    And strugl quite a lotl,
    And if its bulbous neck gets stuck
    Your axolot’l throtl.

    But keep it in a nice dark place,
    And to its fancies pander;
    Then given time and lots of food
    You’ll get — a salamander!

  3. This was great! I wonder how the regenerative cells are different from stem cells. The regenerative cells are probably already coded to what they are supposed to be?
    The lil guys are so cute! I kept a lot reptiles but never ventured into amphibians. Makes me want one! Although my husband jokingly said he would cut a foot off so he could watch it regrow.
    Funny how the biologist said it wasn’t cruel to cut their foot off because they bite each other all day in the wild. Do what you have to do as a biologist – but don’t try to sugar coat it. I’m not saying the axolotl was experiencing pain – who knows. I just disagree with her logic. The things animals do to each other aren’t considered cruel by them – but we can sympathize and know animals would rather avoid being gouged, gored, smashed, eaten alive.

  4. (Will this allow scientists, unlike God, to heal amputees?)

    Don’t be stupid. The correct interpretation is that axolotls are God’s chosen peoplespecies.

    Hence the common greeting among the followers of The One, True™ God: “So I head you like mudkipsaxolotls.”

  5. The axolotl is the only species I know of whose common scientific name (at least in Western parlance) comes from the Aztec.

    Off the top of my head, “chocolate” (Nahuatl “xocolatl”) is a common name for Theobroma cacao. And cacao itself is from “cacahuatl.”

    From this wiki article, we get the following common species/genera names: avocado, chicle, chili, copal, coyote, epizote, mesquite, nopal, ocelot, peyote, sapodilla/sapota, and tomato.

        1. “Tule” also gives us Tule Elk and Tule Perch, who derive their name secondarily from tule, because of their habitat.

    1. Other missing examples: achiote, chayote, hoatzin, jicama, sotol. A couple of those (achiote, chayote) are in the wikipedia list. 🙂

    1. No more you’re not:-)) I will never be able to see it as anything else now!

      Axolotl…s? –ae?…–i? (plural?) are amazing–I first heard of them in, I think, Stephen Jay Gould’s essay on neoteny, and then read about them in more detail in The Ancestor’s Tale.

      I didn’t know they were nearly extinct in the wild! What is being done to protect them?

  6. That made my day to pull up the WEIT site and be greeted by an axolotl. I keep one as a pet (wild type, looks like the last pic) and just find them interesting little animals. Mine is affectionately named “Lotto” because of my husband’s inability to remember what the heck he is. When I first got him (the axolotl, not the husband), my spouse kept calling him the “lotsolotto” and the nickname Lotto stuck.

  7. Hmmm, this must be some new meaning of the word ‘cute,’ of which I was not previously aware!

  8. I’ve loved the axolotl a whole lot’l ever since reading about it in a magazine as a kid.

    The forcibly metamorphized one is… kind of creepy? Is it just me? Just such a weird concept… this secret adult model that doesn’t exist except genetically, until we unleashed it with an injection. I dunno. WEIRD.

    I wonder if the adult phenotype has stagnated/decayed genetically with no natural selection pressure on it.

  9. The axolotls came in healthy and lively! I was very pleased to see
    them packaged carefully, and shipped quickly. They started to eat the
    very same day, and are doing wonderfully!

    All of their fingers are intact, and they look as healthy as can be.
    Thanks for a smooth transaction,

    I’d recommend to all those looking to buy axolotls.

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