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